Alces americanus


Table of Contents


INTRODUCTORY


Cow moose with calves on the Yukon Flats National Wildlife Refuge. US Fish and Wildlife Service photo.


AUTHORSHIP AND CITATION:
Innes, Robin J. 2010. Alces americanus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
ALAM

COMMON NAMES:
moose

TAXONOMY:
The scientific name for moose is Alces americanus (Linnaeus) (Cervidae) [299]. Wilson and Reeder [299] consider Eurasian elk (Alces alces) and moose distinct species. Five subspecies of moose are recognized globally, 4 of which are found in North America:

Alces americanus americanus, eastern moose
Alces americanus andersoni Peterson, northwestern moose
Alces americanus gigas Miller, Alaska moose
Alces americanus shirasi Nelson, Shiras moose [210]

Karyotype, body size, pelage color, size and shape of antlers, skull and dentition morphology, habitat use, and geographical distribution distinguish subspecies [79,82,93,210]. However, the distinction of North American subspecies has been brought into question by genetic analyses. Hundertmark and others [113] found variation in mitochondrial DNA that supported the recognition of the 4 North American subspecies. Conversely, Cronin [59] found no variation in mitochondrial DNA among the 4 subspecies.

Because most studies do not indicate subspecies, this review synthesizes information about moose at the species level but identifies geographic location of moose studies where relevant.

SYNONYMS:
Alces alces Linnaeus [79,82,93,210]

ORDER:
Artiodactyla

CLASS:
Mammal

DISTRIBUTION AND OCCURRENCE

SPECIES: Alces americanus
GENERAL DISTRIBUTION:
Moose is native to North America. The moose's range extends north to about 72 °N latitude and south to about 40 °N latitude [93]. It occurs from Alaska south through the Rocky Mountain region to Colorado; east to Newfoundland; and south to New Hampshire, northern Wisconsin, and northern North Dakota [82]. Alaska moose range from Alaska to western Yukon. Northwestern moose range from eastern Yukon to southern Nunavut; south to central British Columbia; and east to central Ontario and the Upper Peninsula of Michigan. Eastern moose range from central Ontario; east to the Canadian Maritime Provinces; and south to New Hampshire and central New York. Shiras moose range from mountainous areas of southern British Columbia and eastern Alberta; south to northeastern Washington, Idaho, Montana, Wyoming, Colorado, and Utah [79,82,93,189]. Transient moose have been reported as far south as Texas [107]. Outside of North America, moose occur in eastern Siberia and northern Asia [93]. The primary factors limiting the geographic distribution of moose are food and cover in the northern regions and climate in the southern regions [79,123]. NatureServe provides a distributional map of moose.

PLANT COMMUNITIES:
Moose occur in a wide variety of habitats including wetlands, shrublands, and conifer, hardwood, and conifer-hardwood forests in various stages of succession [265]. Moose occur in boreal forest (the taiga biome) from Newfoundland across central and northern Canada to Alaska [123,238,265]. Boreal forest is dominated by spruce (Picea spp.), fir (Abies spp.), larch (Larix spp.), and pine (Pinus spp.), with a mixture of birch (Betula spp.), aspen (Populus spp.), and willow (Salix spp.). Moose occur in arctic tundra in parts of Alaska and northern Canada and in alpine shrublands in northern mountainous areas [40,79]. In the northern Rocky Mountain region, moose occur in temperate conifer forests with spruce (e.g., white (Picea glauca), black (P. mariana), and Engelmann (P. engelmannii) spruce), fir (e.g., grand (Abies grandis) and subalpine (A. lasiocarpa) fir), pine (e.g., lodgepole (Pinus contorta), ponderosa (P. ponderosa), whitebark (P. albicaulis), and limber (P. flexilis) pine), western larch (L. occidentalis), and Douglas-fir (Pseudotsuga menziesii). In the Great Lakes region, southeastern Canada, and northeastern United States, moose occur in mixed-transitional forests in the broad ecotone between boreal forest and temperate hardwood forest, which includes a mixture of maple (Acer spp.), birch, American beech (Fagus grandifolia), spruce (white, black, and red (Picea rubens) spruce), pine (red (Pinus resinosa), eastern white (P. strobus), and jack (P. banksiana) pine), balsam fir (Abies balsamea), tamarack (Larix laricina), and eastern hemlock (Tsuga canadensis). In northwestern Minnesota through southern Manitoba, central Saskatchewan, and eastern Alberta, moose occur in mixed-transitional forests in the transition zone between temperate prairie and boreal forest, where large areas of wetlands and shrublands are interspersed with stands of conifers and hardwoods [123]. This area is often referred to as the "aspen parkland" region [206].

Northern regions: In Alaska, Yukon, and the Northwest Territories, moose occurred seasonally in early- and late-seral boreal forests of white and black spruce, paper birch (Betula papyrifera), and quaking aspen (Populus tremuloides); in glacial river-valley and alluvial-floodplain shrub communities of willow (e.g., Alaska (Salix alaxensis), grayleaf (S. glauca), diamondleaf (S. pulchra), and Bebb (S. bebbiana) willow), alder (e.g., green alder (Alnus viridis)), balsam poplar (P. balsamifera), and birch (e.g., bog (B. glandulosa) and dwarf (B. nana) birch); and alpine and subalpine shrublands [49,90,194,206,288]. In Denali National Park and Preserve in interior Alaska, moose occurred in open stands of white and black spruce with willow understories; brushy alpine communities dominated by resin birch; and riparian willow communities [38]. In southeastern Alaska, moose occurred in a mixture of riparian willow (Alaska, Barclay's (S. barcalyi), undergreen (S. commutata), Sitka (S. sitchensis), and sandbar (S. interior) willow)-black cottonwood (P. balsamifera subsp. trichocarpa)-alder (red (A. rubra) and Sitka (A. viridis subsp. sinuata) alder) habitats, and early-seral (2-29 years old) and old-growth Sitka spruce (Picea sitchensis) and Sitka spruce-western hemlock (Tsuga heterophylla) forests [67]. Ecotones between sedge (Carex spp.) and aquatic habitats were used as moose calving sites throughout Alaska [154].

Rocky Mountains: In the northern and central Rocky Mountains, moose occurred in mixed-conifer forests, quaking aspen forests, and stream valley shrublands and floodplain riparian communities dominated by willows [206,231]. In mountainous southwestern Alberta, quaking aspen and balsam poplar stands and willow-water birch (B. occidentalis) shrublands were important habitats for moose year-round [269]. In northern and central British Columbia, moose occurred in 40- to 80-year-old interior spruce (Picea glauca × P. engelmannii)-subalpine fir stands; interior spruce-lodgepole pine forest; dense, early-successional lodgepole pine-quaking aspen forests; postfire quaking aspen-balsam poplar forest; subalpine birch-willow and birch-willow-interior spruce stands; and lowland bogs with short black spruce, willow, and/or alder thickets [96,224]. In north-central Idaho, moose occurred in old-growth grand fir/Pacific yew (Taxus brevifolia) and subalpine fir forests [208]. Hayden-Wing (1979 cited in [136]) described moose use of open antelope bitterbrush (Purshia tridentata) and chokecherry (Prunus virginiana) habitats in the Juniper Buttes area of Idaho. In the Gravelly-Snowcrest Mountains in southwestern Montana, moose occurred in willow-water birch habitat along streams and wetlands and in quaking aspen, Douglas-fir, lodgepole pine, and Engelmann spruce-subalpine fir forests [203]. In Glacier National Park in northwestern Montana, moose occurred in river floodplain Engelmann spruce-white spruce forest, upland lodgepole pine/subalpine fir forest, upland willow/sedge, and upland quaking aspen habitats [251]. In the Greater Yellowstone area of south-central Montana and northwestern Wyoming, moose most frequently occurred in mature (>300 years old) lodgepole pine forest, mature spruce-fir forest, and riparian willow communities [286]. In the Jackson Hole area of Wyoming, moose occurred in blueberry willow/Geyer's willow (Salix boothii/S. geyeriana), interior willow (S. interior), quaking aspen, big sagebrush (Artemisia tridentata)/antelope bitterbrush, and Engelmann spruce/subalpine fir habitats [109]. In north-central Colorado, moose used lowland willow habitat and mature lodgepole pine forest [136]. In northern Utah, moose occurred in mountain-mahogany (Cercocarpus spp.), serviceberry (Amelanchier spp.), Gambel oak (Quercus gambelii), and quaking aspen stands and burned conifer forest [287].

Central Canada and the Great Lakes region: Moose in this region occurred in flat terrain in conifer, hardwood-conifer, and hardwood forests [79]. Throughout Alberta, moose occurred in old-growth black spruce bogs, old-growth tamarack fens (Bird 1930 cited in [283]), black spruce muskegs, and young quaking aspen stands (≤33 feet (10 m) tall) [237]. On the Superior National Forest, Minnesota, moose occurred in early-successional clearcuts dominated by shrubs and interspersed with balsam fir, black spruce, red pine, and jack pine stands [201]. On Isle Royale, a 210-mile² (544 km²) island in Lake Superior, Michigan, moose occurred in young postfire paper birch-quaking aspen-white spruce; "climax" sugar maple-yellow birch (Acer saccharum-Betula alleghaniensis); mature (80-100 years old) paper birch-aspen-balsam fir-white spruce; "climax" paper birch-balsam fir-white spruce; and lowland northern whitecedar (Thuja occidentalis) and black spruce forests [102,121].

Northeastern United States and eastern Canada: In the northeastern United States, Canadian Maritime Provinces, Ontario, and Quebec, moose occurred in boreal forest, northern hardwood forest, and mixed-transitional forests with American beech, sugar maple, yellow birch, quaking aspen, red spruce, black spruce, balsam fir, white spruce, and eastern white pine [89]. In Newfoundland, moose occurred in balsam fir and balsam fir-white spruce-black spruce forests [279]. Throughout Quebec, moose occurred in paper birch, quaking aspen, paper birch-balsam fir-white spruce, black spruce, and black spruce-balsam fir forests [144,149,223]. In Algonquin Provincial Park in central Ontario, moose calving sites occurred in mature sugar maple forest; eastern hemlock-sugar maple-balsam fir forest; balsam fir-eastern hemlock forest; and sugar maple-balsam fir-paper birch forest. Young sugar maples were dominant in the understories of most forests [3]. Moose used balsam fir-northern whitecedar forest adjacent to a large lake with aquatic vegetation in Sleeping Giant Provincial Park, Ontario. Understories were dominated by young balsam fir and northern whitecedar [87,282]. In Coos County, New Hampshire, moose calving sites occurred in yellow birch-American beech-sugar maple, red spruce-balsam fir, and hardwood-conifer forests [240]. In Maine, moose occurred in mature spruce (white, red, and black spruce)-balsam fir and northern hardwood forests and clearcuts dominated by pin cherry (Prunus pensylvanica), paper birch, quaking aspen, and red maple (Acer rubrum) [226,239].

BIOLOGICAL DATA AND HABITAT REQUIREMENTS

SPECIES: Alces americanus

Numerous reviews describing the biology of moose are available and cited frequently in this review. These include the following comprehensive authoritative sources: [29,79,82,85,93,121,154,265]. Among these sources, this review relies most heavily on this publication: Ecology and Management of the North American Moose (compiled and edited by Franzmann and others 2007 [85]), particularly the following chapters: [18,40,41,47,112,123,142,206,231,245,249,280,289]. This review does not include studies of moose outside of North America. It includes information for many of the life history aspects of the species, but focuses on those life history aspects most relevant to fire. Reviews of fire effects in moose habitats used in this review included these sources: [163,271,280].

LIFE HISTORY:

Physical description: The moose is the largest member of the deer family (Cervidae) [29]. Within their large latitudinal range in North America, moose vary greatly in body size. Moose are smallest in southern parts of the species' distribution [93]. The largest moose occur at approximately 65 °N latitude in Alaska and Yukon [79,93]. Moose become smaller again north of 70 °N latitude [93]. Adult male moose (bulls) may be >40% heavier than adult females (cows) [79]. In Alaska (where moose are some of the largest in the world), bull moose may weigh 1,200 to 1,500 pounds (540-680 kg), and cows may weigh 800 to 1,300 pounds (360-590 kg) [29].

Adult moose have long legs that allow them to travel through deep snow, but depths greater than chest height (approximately >28 inches (70 cm)) hinder moose movements. Snow depths approximately >35 inches (90 cm) often cause moose to reduce movements and restrict activities to small areas (e.g., [79,114,128,210,225,281]) (see Home range). Hard, crusted snow can also make movement difficult and cause injuries to lower legs and hooves [206]. Travel through deep and/or crusted snow is high in energy cost. Deep and/or crusted snow also reduces the availability of food growing near the ground. When snow is shallow, moose paw through it to reach vegetation on the ground. If the snow becomes too deep or encrusted, moose are limited to foraging on plants that are emergent from the snow but within the moose's reach.When snow is deep and/or encrusted, moose frequently move to and remain in places with high canopy cover, where snow may be shallower and/or softer, to conserve energy (see Cover) [231]. In a 1974 review on the influence of snow on moose behavior, Coady [48] concluded that moose movements were not restricted by snow depths <16 inches (40 cm); slight restrictions occurred when snow depths ranged from 16 to 28 inches (40-70 cm); definite impediments to movements occurred when snow depths were >28 inches; and snow depths >35 inches (90 cm) greatly restricted movements and food intake. This suggested that snow depths >35 inches may influence survival and lead to changes in population demographics. Because of their shorter legs, calves may be more restricted by deep snow than adults; similarly, because of their large body size, large males may be least affected by deep snow. Such body size differences may help explain differential movements of sex and age groups during winter in some areas (see Age, gender, and reproductive status) [40,48,281].

An adult moose's large size and long legs help it escape predators [93]. When confronted with a predator, a moose may stand its ground and defend itself by flailing and kicking its legs, or it may flee and attempt to evade the predator by trotting rapidly over obstacles or swimming into deep water that hinders the predator's movements. A moose may also flee to an area that provides better footing, such as areas with shallow snow, and maneuver to confront the predator [40,93]. Large moose tend to stand their ground, whereas small moose tend to flee. Reluctance of large moose to flee from threats contributes to high rates of collision mortality in some populations [40]. A large moose can kill the moose's primary predators—bears (American black bears (Ursus americanus), brown bears (U. arctos), and grizzly bears (U. arctos horribilis)) and gray wolves (Canis lupus)—in its defense. Because of their small size, moose calves are most vulnerable to predation [93]. According to Geist [93], moose calves <330 pounds (150 kg) typically cannot evade predators by fleeing and need maternal protection. Calves >330 pounds may evade predators by fleeing but are typically not able to successfully confront predators on their own. Yearlings >530 pounds (240 kg) may be able to confront predators and successfully defend themselves. A moose's ability to defend itself against predators is particularly important in winter, when snow conditions may curtail movements [93].

Moose have the largest antlers of any living cervid [79]. Only males have antlers [29]. Antlers are palmate and may weigh >77 pounds (35 kg). Bulls begin to grow antlers in mid-March. Most growth occurs in June and July, when antler length may increase by nearly 1.0 inch (2.5 cm)/day [79]. Antler growth and mineralization develop under the velvet [41,79]. The velvet period lasts about 140 days in large bulls in good condition ("prime" bulls) [41]. Antlers are fully developed early to mid-August, and velvet is shed from mid-August to mid-September [79]. Bulls enter the rut—the peak breeding period—shortly after mineralization of the antlers in mid-September [41]. Prime bulls begin to cast their antlers in late November, and casting is generally complete during December or early January [40,79,245]. Prime bulls grow, shed velvet, and cast antlers earliest [79]. Small, young bulls retain their antlers longest, often as late as March [29,40]. Bulls <5 years old do not have fully developed antlers [41]. For more information on this topic, see Growth.

Moose body mass changes seasonally and differs between males and females. According to a comprehensive review, males reach their peak in body mass and condition just before the rut, when they are shedding antler velvet [245]. Sexually active bulls do not eat during the rut and may lose 12% to 19% of their prerut body weight. Small but mature bulls are typically not sexually active and eat during the rut [79]. After the rut, bulls may increase body mass by increasing food intake. Bulls lose additional body mass in winter with natural declines in forage quality and availability (see Nutrition and energetics). Overwinter weight loss can range from 7% to 23% of prerut body mass. Weight gains over summer range from 33% to 41% of postwinter lows. Cow moose reach maximum body weight later than bulls, typically in early winter, after which females lose weight as forage quality and availability decline. Minimum weights are reached shortly after parturition in spring. Cows lose an average of 15% to 19% of their body mass from the midwinter peak to their postpartum lows. Summer gains range from 25% to 43%. Due to the energetic demands of lactation, cows with calves gain less weight in spring and summer than cows without calves [245,273]. Young, maturing individuals generally accumulate fewer fat reserves than adults because of continuing growth [174]. The length and severity of winter, including snow accumulation that restricts mobility and food intake, may determine the extent of annual weight loss and the ability to recover during the rest of the year [173,245].

Physiology: Moose have a summer and winter coat, shedding their coats in spring and fall [82]. Winter coat development is high in energy cost and is associated with a sudden rise in food intake and a stagnation of weight gain. Prime bulls and cows without calves are the first to grow their winter coats. Lactating cows and juveniles molt last [41]. The moose's large body size and insulating coat make it susceptible to heat stress [79]. Moose in winter coats become stressed at temperatures >23 °F (5 °C). In summer coats, moose become stressed at temperatures >59 °F (14 °C) [123]. Moose can apparently tolerate temperatures as low as -40 °F (-40 °C) [123]. In late winter and summer, when temperatures are high enough to elicit panting to dissipate excess heat, moose reduce overall activity and use sites such as the shade of dense conifers or areas near water for cooling [123,231]. Thus, heat tolerance may cause changes in daily activity patterns, limit the use of some habitats by moose, and influence the extent of the species' distribution [79,82].

Courtship and mating: Moose are polygamous and seasonally polyestrous. The rut or peak breeding season occurs from early September to late October, peaking during a 3- to 4-week period [29,79,82,245]. The rut falls within the primary estrous period, with 1 earlier period and up to 2 later periods accounting for a small part of total pregnancies [79,82,245]. In British Columbia, 89% of cow moose conceived within a 10-day period during the rut [77]. Courtship patterns may differ between the rut and other estrous periods [79].

The interval between estrous periods is approximately 22 to 28 days [79,245]. The period of receptiveness for cows within an estrous period lasts 7 to 12 days, but true estrus lasts <24 hours [82]. Females usually mate only once in a given estrous period, whereas males mate multiple times [79]. The largest males with the largest antlers are typically dominant and mate most often [79]. In Alaska, the largest males (those with antler spreads >51 inches (130 cm)) performed 88% of all copulations [290].

The breeding strategies of moose differ across the species' range [245]. Harem mating occurs in tundra-dwelling moose in Alaska and Yukon, where moose congregate in large rutting groups in semiopen subalpine habitats called "rutting areas" [40]. The dominant male herds and defends a group of females without regard to their state of estrus and mates with the females in his group when they come into estrus. Tundra cows reach estrus in synchrony [40,79]. The dominant male generally does not permit other sexually mature males in his rutting group [79], although ≥2 prime bulls may share a harem when it contains >8 females [40]. Rutting groups increase as the rut approaches, are largest during the rut, and decline after the rut. In Alaska, during the second estrus when only 11% of females were bred, the mating system reverted to a tending-bond or serial mating system. In a tending-bond system, a bull pairs with a single female, mates with her, then seeks other mates [79]. Moose presumably switched breeding strategies during the second estrus because there were too few estrous females to make harem mating a worthwhile strategy [248]. A tending-bond system occurs in taiga-dwelling moose. Rutting areas for taiga moose are in forested habitats [79,245]. Bulls travel long distances searching for estrous females. A taiga female's estrus is spontaneous and individualistic [40,145]. Researchers have debated whether high bull numbers are required for all cows to breed during the rut in the tending-bond system. For more information on this topic, see Sex ratios [40].

Reproduction and development: Gestation ranges from 216 to 246 days [29,79,82,245]. Most calving occurs from mid-May to mid-June [245]. The timing of parturition within a population is highly synchronous [79]. In Denali National Park and Preserve, 95% of births occurred during a 16-day period [38]. The need to give birth early, so there is sufficient time during the short growing season for young to acquire body reserves necessary to survive winter, likely determines timing and synchrony of parturition [79]. In interior Alaska, moose born late in spring had higher rates of mortality than moose born early in spring [125]. Predation and weather do not appear to influence timing and synchrony of parturition [38,79].

As parturition approaches, pregnant females move to calving sites [79]. Calves are weaned in the fall when their mother breeds again [29,40,231,245]. Young remain with their mother until the following spring, when their mother drives them away several weeks before giving birth [29,79,82]. Yearlings do not stray far and may reassociate with their mother within a few weeks after parturition [82]. See Home range for more information on this topic.

Growth: Newborn moose calves weigh 24 to 40 pounds (11-18 kg) [29,79,82]. Single calves (36 lb (16 kg)) weigh more than twins (30 lb (13.6 kg)) at birth, but male and female calves weigh the same. Average weight gain for the first 150 to 165 days ranges from 1.3 to 1.6%/day. Growth rates decline after that point, which coincides with the onset of breeding, weaning, and seasonal changes in forage quality. Female growth rate declines twice as fast as male growth rate. This results in females weighing substantially less than males as adults (see Physical description) [245]. Females reach maximum body size at 3 to 4 years old, and males reach maximum size at 7 to 9 years old. Males attain maximum antler size after reaching peak body size [79,93,245]. Body and antler size may decline in moose >12 years old [29].

The age at which a cow moose breeds is related to her growth rate and body size, which are determined by region, weather, and level of nutrition [245]. Females generally first breed when they are 28 months old but occasionally breed at 16 months old. Cow moose on very poor rangelands may not breed until 40 months old [7,29,79,245]. Females typically reproduce yearly, although observations by Albright and Keith [7] in Newfoundland suggested that females on very poor rangelands may not produce calves in consecutive years. A female's maximum reproduction may occur from 4 to 12 years old [82], although Schwartz [245] stated that maximum reproductive output probably occurs from 4 to 7 years old. Reproductive senescence in females typically occurs at >12 years old, although females as old as 18 years may breed [79]. In a declining population in northern Minnesota, reproductive senescence among females was apparent as early as 8 years old [184]. Bull moose are reproductively mature at 16 months. However, young bulls are usually excluded from breeding by more mature males, except perhaps when the adult sex ratio is unbalanced in favor of females (see Sex ratios) [29,79,82,145,245].

Pregnancy and twinning rates: Moose typically have single or twin calves; triplets are rare [82,245]. Twinning rates vary between populations and years. Gasaway and others [91] reported that in 21 moose populations across North America the percent of births that were twins ranged from 0% to 90%. A review from 1981 stated that the percent of adults that are pregnant (range: 75-93%) is consistently higher and less variable than the percent of yearlings (range: 0-46%) that are pregnant [82]. Yearlings that breed generally give birth to single calves [79,245].

Physical condition of maternal females at the time of breeding in fall and at the time they give birth in spring affects pregnancy and twinning rate, weight of neonates, and date of birth, all of which may influence survival of young [29,79,82]. In interior Alaska, females in good condition (high rump fat thickness) in March had higher rates of pregnancy, higher twinning rates, and young with higher birth masses and earlier birth dates than females in poor condition (low rump fat thickness) (P<0.01 for all variables) [125]. A study in south-central Alaska reported female rump fat thickness in fall was positively related with pregnancy and calving rates and negatively with reproductive losses during gestation and neonatal mortality (P<0.05 for all variables) [274].

Moose twinning rates may be related to habitat quality and population density. On the Kenai Peninsula, moose twinning rates were higher in a young (13-14 years old) burn (70% of cows with calves had twins) than an old (30-31 years old) burn (22% of cows with calves had twins) at a time when browse production was peaking on the young burn [84,247]. This suggested that good rangeland conditions on the young burn increased moose productivity [84]. A review of 12 North American studies published prior to 1992 noted that pregnancy rates for yearlings and twinning rates for adults were reduced in populations above carrying capacity. The highest mean adult twinning (47%) and mean yearling pregnancy (65%) rates occurred in populations below carrying capacity. Average adult pregnancy rates, however, were high (84%) irrespective of carrying capacity [31]. Gasaway and others [91] suggested that adult pregnancy rates were highly variable (range: 60-100%) in 21 moose populations across North America, with generally high adult pregnancy rates in populations below carrying capacity (range: 79-100%) and low adult pregnancy rates in populations near or above carrying capacity (range: 60-84%). Researchers in northern Minnesota reported the lowest adult pregnancy rates (48%) in a declining population that showed signs of chronic malnutrition [184]. In a review of fecundity of North American moose, Boer [31] concluded that nutritionally stressed moose populations were likely to show reduced twinning and yearling pregnancy rates, followed by reduced neonate survival, and finally, reduced adult survival. For more information on this topic, see Survival.

Sex ratios: A review of 12 North American studies published prior to 1992 reported that the fetal sex ratio tends towards parity in moose (male: x=51%; female: x =49%), but substantial variation occurs (range: 39-62% male) [31]. Adult sex ratios range from close to parity to skewed towards females [245]. Increased mortality of adult males associated with strenuous and hazardous rutting activities (see Survival) may result in skewed adult sex ratios favoring females [79,245]. Heavy hunting of males also results in adult sex ratios favoring females. The lowest reported adult sex ratio (2 bulls:100 cows) was reported for a heavily hunted Alaska moose population [28]. In a review, Schwartz [245] reported that several studies of tundra moose found no relationship between bull:cow ratios and reproductive success (pregnancy rates, cow:calf ratios) or time of conception. One study on taiga moose in central British Columbia found a positive relationship between twinning rates in females and bull:cow ratios as well as a positive relationship between the proportion of females breeding during the first estrus and bull:cow ratios (P<0.05 for all variables) [6]. These results were attributed, in part, to different breeding strategies of taiga and tundra moose (see Courtship and mating). Another study of taiga moose, however, found no evidence that the density of bulls affected moose reproduction in central Quebec, in part because subadult males (1.5-2.5 years old) bred more frequently in a heavily hunted population compared with an unhunted population [145].

Social behavior: Moose are considered the least gregarious of North American cervids [207,288]. They are not territorial and often overlap home ranges [79,82,112]. They exhibit various degrees of tolerance towards conspecifics, depending upon season, individual age, and gender. When aggregations occur they appear "loose-knit and transitory", except for cows with calves. Cow-calf aggregations are most common [207]. Cows with calves are usually solitary throughout the year and tend to select habitats with cover, probably as a strategy to avoid predators [82,104,112]. Mature bulls are more gregarious and use open habitats more often than cows with calves. Cows without calves are more gregarious than cows with calves [104,112]. Cows without calves and young bulls tend to form the largest groups, often in open habitats [206,207].

Aggregations are most common during the rut and just prior to migration. The largest groups also occur at this time [112,112,177,206,207,207]. In Denali National Park and Preserve, males and females aggregated most frequently during the rut (75% of groups) and after the rut (46%) and least frequently in winter (19%). Males and females aggregated occasionally during the calving period (30%) and during summer (29%). Annually, cows with calves were solitary 99% of the time, except during the rut and after the rut, while only 23% of females without calves were alone [177]. Aggregations may occur on winter ranges when deep snow limits movements to areas where food is abundant [207,231]. Aggregations may also occur at lick sites, particularly in spring and summer [15,149,232].

When aggregations occur, groups of ≤3 moose appear most common, although groups of up to 60 were observed [112]. In Jackson Hole, Wyoming, 58% of moose observations during a 25-month period occurred as single individuals, 26% occurred in groups of 2, and 16% occurred in groups of 3 or more [109]. Moose form larger groups in open habitats than in forest habitats, possibly as a strategy to avoid predators [112,206,207]. In Denali National Park and Preserve, groups in open tundra increased as distance from spruce forest cover—a measure of predation risk— increased (r²=0.07, P<0.004). Solitary animals and groups of 2 foraged almost exclusively in and near cover, but large groups used areas far from cover [180]. On the Kenai Peninsula, Peek and others [207] observed larger groups (up to 15 individuals) above tree line, where moose are more visible to predators, than below tree line (up to 7 individuals). Limited information suggested that denser populations and populations with more females have larger groups [206,207]. Differences in social behavior among age and gender classes contribute to differences in habitat use among these classes [82]. For more information on this topic, see Age, gender, and reproductive status.

Home range and movements: Moose may inhabit the same range throughout the year or migrate to separate summer and winter ranges [79]. Individuals generally retain the same ranges from year to year and travel the same routes between ranges [82,112,153]. However, moose populations pioneering previously unoccupied habitat may not exhibit fidelity to their ranges. In a pioneering population in northern New York, only 25% of bulls used the same ranges during consecutive years, a result attributed to low density of females (1 female:3 males) [89].

Daily activity: Moose are active throughout the day and night. Moose activity patterns are highly variable between seasons and among individuals in a population, although peaks of activity often occur around dusk and dawn. Crepuscular activity is less pronounced in winter, especially at high latitude, where hours of daylight are limited. High temperatures during the day, particularly in summer, may cause moose to be more active at night [79,82].

Seasonal movements and migration: Moose may inhabit the same range throughout the year or migrate to separate summer and winter ranges in spring and fall (see Home range) [79,153,265]. A period of movement to rutting areas occurs in fall. Researchers often consider rutting areas or fall ranges as part of summer ranges [112,265], although some consider rutting areas part of winter ranges [170]. Some researchers identify calving sites as distinct spring ranges [112,153,265]. During severe winter weather, moose may concentrate their movements in small areas with shallow snow within winter ranges called "winter yards" [79,112,280].

Most moose populations contain migratory and nonmigratory segments, although some populations are totally nonmigratory. Nonmigratory moose remain on the same range during winter and summer presumably because winter environmental conditions are favorable [112]. On flat terrain in the Upper Peninsula of Michigan, 22% to 38% of moose migrated in a given year [66]. In mountainous west-central British Columbia, where snowpack and duration of snow cover increase with elevation, >70% of moose were migratory [65].

Migratory and nonmigratory segments of a population may exhibit different behaviors and thus have different population demographics. A review of moose populations on the Kenai National Moose Range reported that migratory moose in the area moved long distances between winter and summer ranges, had low population densities and large summer home ranges, occupied traditional rutting areas in mountainous drainages, and aggregated in groups during the rut. In contrast, nonmigratory moose occupied lowland areas year-round, had relatively sedentary habits and high population densities, had small home ranges, and showed solitary behavior. Both population segments had a low proportion of bulls, due in part to heavy bull hunting [17].

The timing of migration depends in part on weather. Moose may leave summer ranges in response to accumulation of deep snow or remain on summer ranges if snow is shallow. Moose may leave winter ranges with snowmelt in spring [19,79,104,109,112,170]. In mountainous areas moose typically seek low elevations in winter—where snow depth and hardness may be less—and return to high elevations in summer—where forage quality and quantity may be greater [48,79]. In the Gravelly-Snowcrest Mountains in southwestern Montana, moose concentrated in lowland winter ranges dominated by willow at about 6,500 feet (2,000 m) elevation [203], often moving to adjacent conifer cover during severe winter weather [130]. With vegetation green-up, moose moved to subalpine meadows on summer range at 7,500 to 8,500 feet (2,300-2,600 m) elevation [130,203]. In October, moose moved to the upper limits of their summer range and remained there until early winter, when they returned to lowland winter range. Moose appeared to remain on the high-elevation summer range until deep snow made browse unavailable [203]. In northern British Columbia, moose used the lowest elevations during calving; gradually moved upslope during summer and fall; reached their highest elevations in early winter; and moved progressively lower in late winter until calving [96]. Alternatively, moose may move up to high elevations in winter if snow is shallow and forage is available [93,112]. In eastern Alaska and western Yukon, nearly 90% of moose migrated from low-elevation (970-1,070 feet (295-325 m)) summer ranges to high-elevation (2,000-3,440 feet (610-1,050 m)) winter ranges [170]. Moose also migrate in areas with level terrain [135]. The rate of migration varies within a population [112]. Van Ballenberghe (1978 cited in [112]) reported that individual moose took from 10 days to 6 weeks to cover the same distance between summer and winter ranges.

Usually moose migrate singly or in small groups, often following traditional routes. Migration in moose is apparently a learned behavior. Young moose follow the movement patterns of their mothers and acquire their mother's seasonal ranges and migration routes [79,112].

In general, populations living in mountainous regions migrate further than populations residing in flat terrain. Migratory distances appear to be longest in Alaska. Migration distances vary within and among populations. Migration distances reported in a review of 9 North American studies ranged from 1 to 58 miles (2-94 km) [112]. Maximum distances between summer and winter range ranged from 12 to 122 miles (19-196 km) in eastern Alaska and western Yukon [170]. In contrast, migration distances ranged from 1 to 16 miles (2-26 km) in the Upper Peninsula of Michigan [66]. In Jackson Hole, Wyoming, 18 moose moved 5 to 10 miles (8-16 km) between summer and winter ranges, 4 moose moved >20 miles (32 km), and 4 moose used the same area during winter and summer [109].

Dispersal: Young and adult moose disperse, but dispersers are mostly subadult males [112]. Young moose may disperse or remain near their natal areas. Gasaway and others (1985a cited in [79]) reported that 97% of young moose in a moderately dense population in interior Alaska established home ranges that overlapped the home ranges of their mothers. Moose that disperse typically do so during their second year (see Home range) [79]. In the Upper Peninsula of Michigan, 6% of moose dispersed and 83% of dispersers were yearlings [66].

Female moose are more likely than males to establish home ranges overlapping with those of their mothers [79]. A pioneering population of moose in northern New York was biased towards males by 3:1, a result attributed to higher rates of male dispersal [89]. A 5-fold increase in moose populations 2 winters after a May wildfire in northeastern Minnesota was attributed to immigration of subadult males into the burned area [205]. Conversely, moose dispersal during the first year after a fire in central Alaska resulted in a 5- to 6-fold increase in use of the burn, but dispersing male yearlings did not appear to increase use of the burn more than other age or gender groups [90]. In southern Quebec, male and female moose dispersal frequency was similar; 58% of young moose did not disperse, 30% dispersed, and 12% exhibited erratic movements or "partial dispersal" [138].

Dispersal movements vary greatly but are typically short [79]. Gasaway and others (1985b cited in [112]) reported a mean dispersal of 2 miles (3 km) after the first year of independence from their mothers for 18 moose in interior Alaska. The longest dispersal distance reported as of this writing (2010) was by a young male that traveled 939 miles (1,511 km) from South Dakota to Texas in 509 days [107].

Because moose use traditional ranges and travel routes, they are most likely to disperse to newly created habitat if the habitat overlaps an existing home range or migration route [90,138,153]. Moose exhibited limited dispersal into a 193-mile² (500 km²) burned area in black spruce/quaking aspen lowland in central Alaska despite being located 0.1 to 3.0 miles (0.2-4.8 km) from the edge of the burn [90,92]. Moose increased use of the burn and established new movement patterns that incorporated the burn mostly during summer and during migrations to rutting areas the first year following the fire [90]. For more information on this study, see Travel patterns. Although many moose movements are traditional, moose may be nomadic, which can lead to dispersal [82].

Home range: A review of 16 North American studies reported total moose home range sizes (where migratory movements were included in some estimates) ranging from 0.3 to 746 mile² (0.8-1,932 km²) [112]. Home ranges are generally similar between genders except perhaps in spring during calving, when female movements decrease, and during the rut, when male movements increase [79,112].

The size of seasonal home ranges depends on region, topography, weather, and individual age, gender, and reproductive status [112]. Seasonal home ranges are often larger in northern than southern parts of the moose's distribution. Hundertmark [112] plotted winter and summer home range sizes against study area latitude in 13 studies and found that between 40 °N and 60 °N latitude, mean sizes of winter and summer home ranges remained relatively stable at ≤20 miles² (51 km²). Above 60 °N latitude, home ranges and variation among individuals generally increased. This trend presumably reflected differences in distribution and productivity of seasonal habitats across the moose's range [112]. Van Ballenberghe [288] suggested that moose in Denali National Park and Preserve had larger home ranges than elsewhere because of the patchy distribution of productive habitat. Along the Susitna River in Alaska, Taylor and Ballard (1979 cited in [112]) found small home ranges for moose in mountainous habitat and large home ranges for moose in lowlands and concluded that terrain influenced home range size.

No consistent pattern is evident regarding size of seasonal home ranges. In summer, moose may move long distances and expand their home ranges to access aquatic habitats and lick sites where these features are available [112]. In Denali National Park and Preserve, moose moved up to 5 miles (8 km) from the center of their home ranges to a lick site, apparently the only one available in the area [288]. Leptich and Gilbert [152] reported that moose home ranges in northern Maine varied from 1 to 23 miles² (2-60 km²), with much of the variation explained by the distribution of aquatic habitats used as feeding sites. Home ranges encircling aquatic feeding sites were small, whereas home ranges with an aquatic site on one end were large, long, and narrow. Moose in northern New Hampshire elongated home ranges during summer and/or fall to encompass at least one roadside salt lick [175]. Conversely, at the Laurentides Wildlife Reserve in Quebec, many moose used salt licks, but not all moose had a salt lick in their home range, and not all moose that had salt licks in their home range visited them [144].

In winter, when deep snow limits mobility or access to food, moose may limit their movements to small areas with shallow snow within their winter range [79,82,112]. In New Brunswick, moose used 63% of a 58-mile² (93 km²) area in late June compared with 13% of that area when snow was deep in early April (Telfer 1968b cited in [265]). On Isle Royale, moose used home ranges averaging 9.3 miles² (15.0 km²) when snow was 16 to 26 inches (40-65 cm) deep but moved into northern whitecedar lowlands and reduced home ranges to 3.6 miles² (5.8 km²) when snow was 32 to 39 inches (80-100 cm) deep [234]. In northeastern Minnesota, a cow moose was observed occupying a 6-acre (2.4 ha) area in a balsam fir stand during a month-long period of deep snow (range: 35-52 inches (89-132 cm)) [291]. In northern Maine, Thompson (1987 cited in [112]) observed median winter home ranges of 2.7 miles² (7.1 km²) during a year with low snow depths, but home ranges were 0.6 mile² (1.6 km²) during the subsequent winter, when snow depths were often >28 inches (70 cm). However, in many locations in a given year, snow depths do not affect moose movements and habitat use [112]. In northwestern Quebec, moose used a smaller area in late than early winter, but this was not due to an increase in snow depth. Other factors, such as poor physical condition or heat stress, might have reduced moose activity in late winter (abstract by [122]). For more information on this topic, see Cover.

During the rut, males increase movements and often have large home ranges, whereas females often reduce movements and home ranges. This is attributed to the moose's polygamous mating system and large movements to rutting areas by bulls (see Courtship and mating) [79,112]. Such movements may depend on the density of breeding males. In a Jackson Hole, Wyoming, population with abundant males, most bull locations during the rut (69%) were >2.5 miles (4 km) from the center of their summer ranges, whereas most cow locations (80%) were <1 mile (1.6 km) from the center of their summer ranges [109]. However, where bull density is low, cows may expand their home ranges and movements during the rut. LeResche [153] observed large-scale movements by females during the rut in a population with a low bull:cow ratio. In contrast, other researchers reported similar home range size between males and females during the rut despite low bull:cow ratios [145].

In spring during parturition, cows with calves often have the smallest home ranges. LeResche [153] summarized age- and gender-specific trends in home range size of moose in 1974. He noted that cows with newborn calves restricted their movements for the first 3 weeks after parturition to calving sites, after which they gradually expanded their home range to sizes similar to those of other adults. Young moose accompany and consequently have the same home range as their mother during the first year of life [79,112]. In south-central Alaska, most young separated from their mother at 12 to 16 months old (range: 10-28 months old) [19]. A yearling moose is most likely to rejoin its mother if her newborn calf or calves die [19,112]. In south-central Alaska, cows that lost a calf within 10 days of parturition were likely to reassociate with their yearlings (P=0.058), but reassociation did not occur if the calf died after 10 days of age. Yearlings that reassociated with their mothers had increased survival (91%) compared with independent yearlings (33%) (P=0.04) [273]. After independence from their mother, young moose may remain in close proximity to their mother, often wandering without fidelity to specific areas. Young moose usually separate permanently from their mother and establish home ranges during their second year [79,112].

Population density: Moose densities range from <0.1 to >24 moose/mile² (0.04-9.3/km²). Highest densities generally occur in "park situations" where hunting is not permitted and predation is absent or minimal [123]. A review of moose population history on the northern Yellowstone winter range stated that long-term studies in North America showed that moose populations consistently erupt, crash, and then stabilize at various densities depending upon ecological conditions and hunting or predation pressure [285]. Population densities may also fluctuate in response to a complex interaction with parasites and diseases, malnutrition, and weather [29,123,184]. Food supply plays an important role in regulating moose populations through a complex set of interactions with nutrition and its influence on reproduction [289]. Based on expert opinion, Telfer [265] stated that the lowest moose densities occur in arctic tundra and arctic tundra-taiga transition rangelands where gross primary productivity is low; intermediate densities occur in boreal and conifer-hardwood transition rangelands; and highest densities occur in productive hardwood forest rangelands with soft, thin snow. Because of the importance of early-seral browse in the moose's diet, moose populations may increase rapidly after fire or other disturbance that creates early-successional habitat (see Indirect Fire Effects).

Survival: Moose exhibit a U-shaped curve with respect to mortality rate and age. On Isle Royale, an unhunted moose population had high mortality (>60%) among very young (<1 year old) and very old (>15 years old) age classes and low mortality among adults; mortality was lowest (<11%) between the ages of 1 and 6 and increased rapidly thereafter. Mortality was >20% for moose older than 10 years (Peterson 1977 cited in [289]). Survival rates of calves and adults vary depending primarily on hunting and predation pressure, malnutrition, and accidents [47,289]. Mortality may be most extensive in moose populations during severe winters [289]. Bishop and Rausch [28] documented substantial winter mortality, mainly of calves but also adults, for 4 high-density Alaska moose populations during severe winters. Moose appear most susceptible to mortality caused by predation by gray wolves; collisions with trains and vehicles; and malnutrition during severe winters [79]. Because weather may affect survival, long term climatic changes may cause changes in moose distribution and abundance.

Hunting: According to reviews, adult survival rates range from 75% to 95% and depend in part on hunting pressure [79,289]. High hunting mortality can reduce moose population density and skew adult sex ratios [289]. An unhunted population on Isle Royale had an average annual survival of 87% for adult males and 88% for adult females (Peterson 1977 cited in [289]). Annual survival of adult and yearling males in south-central Alaska during a 10-year period averaged 75% and 91%, respectively, in a population where hunting was the major mortality factor; that of unhunted adult and yearling females averaged 94% and 95%, respectively [19]. High hunting pressure on adult male moose can result in adult sex ratios highly skewed towards females [289].

Predators: A comprehensive 2007 review stated that predation by gray wolves and bears may limit moose populations under certain ecological conditions. Other studies suggested that other factors, such as weather or forage quality, can be as important in limiting moose populations as predation [289].

Predation is the primary source of mortality for young moose in many populations [79,289]. Predators may account for up to 80% of neonate deaths [289]. Most calves are killed by predators soon after birth. In northeastern Alberta, where predation by gray wolves and bears was the primary cause of calf mortality, calf survival was lowest in the first 30 days of life (61%), whereas calf survival after 30 days until 1 year old was 95% [104]. Moose calf mortality in south-central Alaska, where brown bears were the predominant source of mortality on calves, declined in a linear fashion from birth to 65 days old [272]. Maternal females may be most vulnerable to predation during the calving period because they are less mobile than nonparous females and because they defend newborn calves [143]. In south-central Alaska, mortality rates of female moose in early summer during a 6-year period was significantly higher among females with calves (10%) than females without calves (4%) (P=0.04) [273].

Bears kill adult moose but are especially important predators of calves in spring and summer. Because bears hibernate, they do not contribute to moose mortality in winter. Gray wolves kill moose of all ages and genders in physical conditions ranging from poor to good. Gray wolves kill moose as single individuals, in pairs, and in large groups [79]. On the Kenai Peninsula, gray wolves selectively killed calves and moose >12 years old [211]. However, another study on the Kenai Peninsula during a severe winter found no evidence that gray wolves selected weak, young, or old moose [83]. Feldhamer and others [79] attributed differences between the studies to the fact that gray wolves kill vulnerable individuals and many conditions affected vulnerability, including snow conditions.

Deep snow may make moose more vulnerable to predation by gray wolves [79,289]. During a 50-year study on the Kenai Peninsula, where moose are the most frequent prey item in gray wolf diets during all seasons, moose predation was highest in winter and more moose calves were killed during winters with deep snow [211]. When snow depths on Isle Royale exceeded 30 inches (76 cm), the percentage of calves in the gray wolf kill increased (Peterson 1977 cited in [20]). A 40-year study on Isle Royale reported that during winters with deep snow, gray wolves hunted in larger packs and killed 3 times the number of moose/day compared with winters with shallow snow. Following increased predation, moose abundance declined; and following release from heavy browsing, growth of understory balsam fir increased [217].

Malnutrition: Nutritional deficiencies are often associated with poor-quality habitats (see Forage site selection), but deep snow can bury and reduce access to forage even in high-quality habitats, which can lead to malnutrition, starvation, and ultimately death. In an 11-year study in the lower Susitna River Valley, south-central Alaska, malnutrition was the main cause of mortality during severe winters (deep (≥41 inches (104 cm)) and persistent snow pack) in a population with low predation pressure [179]. In southeastern Alaska, prolonged deep snow restricted access to forage and resulted in starvation and subsequent moose population decline [29].

Because adult males have lower fat reserves in fall due to rutting activities, adult males may have higher mortality rates during severe winter weather than adult females. Calves of the year may have higher mortality rates during severe winter weather than adults due to their growth requirements and lack of fat reserves (see Physical description) [289]. On the Kenai Peninsula, a complex of factors leading to malnutrition, primarily related to snow depth, density, hardness, and persistence, was responsible for the death of nearly all calves during a single winter (Franzmann 1978 cited in [82]). Peaks in calf production appeared to be related to successive years of mild winter weather, and consecutive years of severe winter weather appeared to result in sharp drops in calf production. A single severe winter did not result in noticeable changes in reproductive patterns and/or densities of moose [21]. In northeastern Idaho, where predators were sparse, deaths attributed to malnutrition were recorded for 7 consecutive winters of above-average severity, and as many adult deaths as calf deaths were attributed to malnutrition [235].

Summer weather conditions may also influence moose survival. In a review of moose population dynamics, Van Ballenberghe and Ballard [289] reported that cloudy, wet summers may improve forage quality, which in turn may improve moose body growth and fat storage. Thus, they suggested that summer may be a critical season for moose because the size of fat and protein stores accumulated during summer in part determines how long animals survive in a negative energy balance during winter [289]. See Nutrition and energetics for more information on this topic.

Life span: In the wild, few moose live >16 years, although some cows reportedly lived >20 years [29]. Females may live longer than males. Analyses of an unhunted moose population on Isle Royale found that females and males that survived their first year had mean life expectancies of 7.8 and 7.0 years, respectively. Males lived up to 15.5 years and females lived up to 19.5 years (Peterson 1977 cited in [289]).

DISEASES AND SOURCES OF MORTALITY:
Sources of moose mortality include parasites and diseases, predators, hunting, fire, accidents, and malnutrition [289]. Numerous parasites infest moose, including flatworms (e.g., giant liver flukes, rumen flukes (Paramphistomum spp.), and tapeworms (hydatid worm (Echinococcus granulosus) and Taenia spp.), nematodes (e.g., meningeal worms, tissue worms (Elaphostrongylus spp.), and lung nematodes (Dictyocaulus viviparus)), ticks (e.g., winter ticks), and flies (order Diptera). However, according to a comprehensive review, only a few parasites and diseases that infest North American moose limit moose numbers. These include the meningeal worm (Parelaphostrongylus tenuis), which causes the neurological disease parelaphostrongylosis, and the winter tick (Dermacentor albipictus) [142]. Giant liver flukes (Fascioloides magna) were the major cause of moose mortality in a declining population in northern Minnesota, with up to 89% of deaths attributed to this parasite, but evidence that giant liver flukes contributed to moose population declines in other areas was sparse [184]. Parasites and diseases that affect the moose's primary predators, such as canine parvovirus, may indirectly affect moose mortality. For a comprehensive review of diseases and parasites that infest moose, see these references: [79,142]. Bears and gray wolves are principal moose predators in North America and kill young and adult moose. Because bears hibernate in winter, gray wolves are considered the only winter predator of moose throughout moose's boreal range capable of affecting moose population dynamics [18,79].

Accidents: In unhunted populations, accidents may kill more adult moose annually than other mortality factors. Accidents commonly affecting young and adult moose include motor vehicle and train collisions, entrapment (such as miring in deep marshes), abandonment of young by the mother, and drowning (especially falling through ice) [47,82]. In a 10-year study of nonhunting moose mortality in northeastern Ontario, 64% died in collisions or other accidents [47]. Collisions with motor vehicles and trains are responsible for thousands of moose deaths each year. Moose are attracted to transportation corridors because their preferred early-successional habitat and forage are often available along roadways and railways [47,79,82]. Roadways and railways provide travel routes for moose through deep snow, and collision deaths are highest during periods of deep snow. In an 11-year study in the lower Susitna River Valley, south-central Alaska, 64% of all moose train kills occurred during 2 deep-snow winters [179]. In addition, moose are attracted to roadways by salt pools created by salting highways in winter to prevent icing (see Lick sites) [149]. Presence of roadside salt pools increased the likelihood of moose-vehicle collisions by 80% in Quebec (Grenier 1974 cited in [149]).

Aggressive fighting between males during the rut occasionally results in severe injury and rarely death [29,47,79,82,93]. Rut-related injuries may make male moose more vulnerable to predators or impair their ability to survive severe winter weather. Large males cease feeding during the rut, which may further compromise their energy reserves and their ability to survive severe winters (see Courtship and mating) [79].

PREFERRED HABITAT:
In general, moose tend to select habitats that offer the highest density, highest biomass, and most nutritious forage [206,269,280]. Habitat use may be modified by weather (e.g., snow accumulation and temperature; see Cover); rutting activity; calving; presence of lick sites and aquatic habitats; predators; population density; individual age, gender, and reproductive status; and juxtaposition of habitats providing food and cover [206]. Across the moose's range in North America, important moose habitats include mature, closed-canopy conifer or conifer-hardwood forests and high forage-producing, early-successional forests, shrublands, and aquatic habitats [79,93,206]. Moose appear to require both young and old forests in their home ranges [276]. Seasonally, moose use high forage-producing, open-canopy habitats in spring and early summer and again in late fall and early winter. They shift to denser cover in late summer and in midwinter. Habitat use is largely governed by forage availability, except when severe winter weather favors use of closed-canopy forests [201].

According to a comprehensive review of moose habitats in North America, "typical" habitat providing abundant herbaceous forage and deciduous browse includes shrubby, open upland habitats—such as logged areas, burns in early succession, and subalpine shrublands—and aquatic habitats in spring and early summer [206]. Closed-canopy areas are often used in late summer for protection from extreme heat [265]. Moose return to shrubby, open upland areas—such as large stands of shrubs and saplings—in fall and early winter during the rut and prior to migration [206,265]. Closed-canopy areas—tall shrub communities or tall closed-canopy conifer and hardwood-conifer stands—are used in late winter when forage quantity and nutritive quantity is lowest and moose seek areas sheltered from snow [206]. Moose may remain in shrubby, open habitats throughout winter if snow is soft and shallow and forage remains accessible [265].

In mountainous terrain, regardless of region, moose tend to occupy subalpine forests, timberline forest-shrubland mosaics, and shrublands above timberline in summer and early fall [206,265]. Because snow depths are often less at low elevations, moose often move from high elevations in early winter to low elevations in late winter. In late fall in mountainous terrain, moose typically migrate into lowland shrubfields in old burns or logged areas or into floodplain riparian vegetation, remaining there through winter [206]. In some regions, snow depth is lower at wind-blown, high-elevation sites than at low-elevation sites, and the reverse pattern is exhibited (see Seasonal movements and migration).

In flat terrain, moose use aquatic habitats and open upland sites such as aspen and willow stands in summer. Late-winter habitat in flat terrain is usually dense conifer forest. In tundra, moose occupy riparian shrublands year-round and adjacent uplands with sparse shrubs in summer [265]. On the basis of total year-round use, shrublands, particularly willow habitats, are the most preferred habitat throughout the moose's range [200,265].

Forage: For information on moose habitat use relative to forage quantity and quality, see Forage site selection.

Cover: Moose most commonly select closed-canopy communities in late summer and late winter. They most commonly select open-canopy communities during late fall, early winter, and spring. Deep and/or crusted snow and high temperatures cause moose to seek closed-canopy habitats. Moose habitat use varies between years, reflecting differences in weather [209].

Summer: Moose may shift from open habitats in early summer to cool, closed-canopy habitats in late summer for protection from heat when temperatures may exceed maximum critical temperatures (see Physiology) [20,265]. In mixed-transitional forests on Superior National Forest, Minnesota, moose of mixed ages and genders preferentially occupied aquatic areas, young (<20 years old) quaking aspen/paper birch stands, and upland mature balsam fir stands in early summer. Of these habitats, open stands (<988 trees/ha) with short (<49 feet (15 m) tall), young trees were preferred. In mid- to late summer, "moderately stocked" upland stands of quaking aspen and paper birch and lowland stands of black spruce, quaking aspen, and balsam fir were used more than expected compared to availability, suggesting a shift away from the most open areas. In late summer, moose movements generally decreased, and moose shifted to mature stands (>50 years old) [201]. During a 3-year study in southwestern Montana, moose tended to use closed-canopy aspen and conifer forest during dry, hot summers and more open canopy cover during cool, wet summers [202].

Winter: During winter, snow depth is often a major determinant of moose distribution because it reduces forage availability and restricts movement (see Physical description). During mild winter weather, moose often use forests with patchy tree cover and shrubs, where forage is abundant. Moose shift to closed-canopy conifer habitats if snow conditions become severe [79,133]. A 1996 review reported that 14 studies indicated increased use of, and movement into, microsites with dense conifer cover when snow was deep and encrusted [20].

Moose foraging in snow. Photo courtesy of La Verne Smith, US Fish and Wildlife Service.  

High overstory cover often characterizes winter habitat for moose because it intercepts snow, which lowers locomotion costs and/or increases browse availability relative to other available habitats [20,79,81,206]. In the mixed-transitional forest region of central New Brunswick, moose used open hardwood and conifer forest in January when snow was 11 to 19 inches (28-48 cm) deep. They used dense (basal area: >75 ft²/acre) conifer forest in March significantly more than available when snow was 30 to 44 inches (76-112 cm) deep (P<0.05) [267]. In northern New Hampshire, moose preferred 5- to 20-year-old logged areas during winter, only moving to areas with balsam fir cover when snow exceeded 36 inches (91 cm) [298]. In mixed-transitional forests on the Superior National Forest, moose preferred sparsely stocked clearcuts <20 years old before the rut. During the rut, they preferred mature (>50 years old) moist, lowland habitats. After the rut, moose again preferred open habitat (clearcuts <20 years old) containing abundant forage. Open habitats still were preferred in early winter, but moose gradually shifted to 40-year-old closed-canopy balsam fir-black spruce stands as snow accumulated during midwinter. In general, closed-canopy stands were used most often during severe winter conditions, whereas open forests were used during mild conditions [201]. In central Alberta, moose shifted from open lowland habitats in early winter to upland habitats with dense canopy cover in late winter because of increased snow depth in lowland areas. Lowland use was negatively related to mean monthly snow depths (r²=0.30, P<0.05) [237]. On the Upper Peninsula of Michigan, in late winter when snow was deep (>50 inches (127 cm)), moose of all ages and genders selected denser canopies at bedding sites (calves 74%, cows 66%, and bulls 52%) than available at nearby random points (P<0.002 for all variables), but no such difference was found in early winter when snow was shallow (<50 inches) [176]. In north-central Idaho when average snow depth in open areas was >30 inches (75 cm), moose movements were restricted to multicanopied old-growth forests where snow depth averaged 7 inches (18 cm) [213]. In southeastern Alaska during a winter of below-average snowfall, moose preferred hardwood stands; used conifer stands, hardwood-conifer stands, and logged areas in proportion to availability; and avoided open areas. During an above-average snowfall winter, moose used conifer and hardwood-conifer stands more, and hardwood stands and logged areas less, than in the below-average snow winter (P<0.01 for all variables) [114]. Racey and Racey [225] found that conifer species and tree spacing determined a habitat's ability to intercept snowfall and provide thermal protection for moose in southwestern Ontario. Forty-year-old black spruce stands >39 feet (12 m) tall and spaced at 11.8 feet (3.6 m) did not provide adequate protection from deep snow, but black spruce stands with 5.9-foot (1.8 m) spacing provided protection. The authors suggested that most conifer species would provide sufficient protection for moose from deep snow at 5.9-foot spacing [225].

Conifer forests most often provide late-winter cover for moose, but the amount of conifer cover in stands used in late winter appears highly variable. In southern Quebec, winter yards had a multicanopied forest structure with a wide range of canopy closures (range: 41-80%) and canopy heights (range: 30-69 feet (9-21 m)) [223]. Moose often use small pockets of conifer cover in hardwood and hardwood-conifer forests. McNicol and Gilbert (1978 cited in [78]) found that 80% of moose winter bedding sites in 10- to 15-year-old clearcuts were associated with young (1.0-3.0 inches (2.5-7.6 cm) DBH) conifer clumps. In northeastern Ontario, moose use of forest stands changed as winter progressed. In late February and late March during 2 winters, moose preferred hardwood-conifer stands over conifer stands or open areas. In late February, moose showed no preference for any particular hardwood-conifer stand type, but in late March, moose preferred hardwood-conifer stands with abundant balsam fir, which accounted for >50% of the winter diet [51]. Several researchers suggested that moose select hardwood-conifer stands in winter during periods of deep snow because these stands offer a good interspersion of forage and cover at a time when movements are limited ([51,114], Dussault 2000 cited in [71]).

Whether conifer or hardwood-conifer stands are used in winter, a juxtaposition of relatively open habitat with good forage availability next to closed habitat providing escape cover and a suitable microclimate appears important in moose habitat selection. In Denali National Park and Preserve, 96% of moose groups foraging on willows in open tundra from late May through early September were ≤164 feet (50 m) from cover of spruce forest [180]. In southeast Ontario, moose decreased browse use with increased distance from cover in 5- to 6-year-old clearcuts. Use decreased beyond 260 feet (80 m) from cover (P<0.01) [100]. In northwestern Quebec, moose home ranges were located in areas with high amounts of edge and interspersion among habitat patches [54]. Moose commonly select edge habitat apparently because of close proximity of habitats providing food and cover (e.g., [22,54,100,116,154,187,276,280]).For more information on this topic, see Logging and Burn size and shape. Bubenik [40] speculated that taiga moose and tundra moose may have different habitat juxtaposition requirements because taiga moose prefer disturbed areas for feeding and often seek escape in the forest, whereas tundra moose prefer more open areas and seek escape into the open.

Moose may not increase use of closed-canopy conifer forest when snow deepens, especially if conifer habitats do not have reduced snow cover. Schwab and others [243] reported that browse burial increased with increased conifer canopy cover in north-central British Columbia, and open, wind-exposed logged sites provided the most accessible forage to moose in winter. The authors suggested that logged areas may provide better moose habitat in winter than unlogged areas [243]. However, the authors did not determine how moose were using the different habitats. In North Park, Colorado, some moose used antelope bitterbrush and mountain-mahogany habitats on slopes where forage was exposed by wind during winter [16]. In the Susitna River floodplain in south-central Alaska, moose preferentially traveled along nonvegetated, windblown sites such as dry sloughs and frozen river channels during periods of deep snow because these areas had shallower snow than other sites (P<0.05) [49]. On the Seward Peninsula in western Alaska, moose occurred in riparian willow habitats 92% of the time in late winter. They utilized windswept areas of the river and gravel bars with shallow snow to access the linear bands of willow habitat along the river [95].

Moose may move to conifer habitats in late winter for reasons other than snow conditions, such as presence of abundant and/or nutritive forage or to avoid predators. On Isle Royale, moose moved into northern whitecedar bottomland and reduced daily movements during periods of deep snow (32-39 inches (80-100 cm)) [234]. Because average snow depth was not less in the bottomlands but was more variable, Renecker and Schwartz [231] attributed the increased use of bottomland areas during deep snow conditions to increased availability of high-quantity but low-quality browse in bottomlands. In south-central Alaska moose selected alder-willow communities during a deep snow winter, although overstory cover was often sparse because this habitat provided the greatest access to preferred willow browse [262]. Other researchers reported that conifer habitats had relatively more available, more nutritive browse than other available habitats in late winter, which likely explained moose use of these habitats. For more information this topic, see Forage site selection. In late winter, moose may be in poor physical condition (see Physical description) and be heat stressed when temperatures exceed 23 °F (5 °C) (see Physiology), another explanation for reduced movements and moose use of conifer habitats at this time.

According to a review of moose habitat use in North America, conifer cover does not appear to be a major component of moose winter habitats in regions where snow depth is usually <35 inches (90 cm) or in regions with little or no conifer cover [206]. In these areas, moose often concentrate in habitats with low overstory cover where food is abundant in winter, including river deltas and riparian zones with willows, rather than where snow is sparse [79]. In north-central Alaska, nonmigratory moose preferred river floodplains dominated by tall (>7 feet (2 m)) shrubs year-round. Moose appeared to congregate in the tall-shrub river floodplains throughout the year because of both high cover provided by the tall shrubs and abundant browse [183]. The review concluded that in deep-snow areas where conifers are absent, moose select microsites with combinations of shrub canopies and topographical situations, such as south-facing or wind-blown slopes, that reduce snow depths [206].

Age, gender, and reproductive status: Except during the rut, moose habitat use typically differs among males and females during much of the year. Spatial segregation apparently occurs because adult males select habitat with greatest forage abundance, while females—especially cows with calves in summer—select habitats with greater cover [36,177]. Miquelle and others [177] observed segregation of male and female moose in Denali National Park and Preserve and found that segregation was greatest in winter and with large bulls. The authors speculated that because of their larger body size and postrut energy deficit, large bulls were more prone to malnutrition in winter than other age or gender classes, causing them to move to areas with high forage biomass but deep snow, whereas other age and gender classes foraged in areas with low forage availability but low snow depths [177]. Many researchers reported that cows with calves sought heavier cover than other adults (e.g., [36,72,176,177,202,281]). Peek [202] noted that bulls and cows without calves made greater use of open areas than cows with calves during summer in southwestern Montana. In the Upper Peninsula of Michigan in winter, cows and calves bedded in denser eastern hemlock stands (75% canopy cover) than bulls, probably because calves needed shallower snow to avoid predators. Bull bedding sites were found in less dense balsam fir (57% canopy cover), probably because this habitat was abundant and provided some shelter as well as food [176]. In interior Alaska, males moved into a mechanically-crushed feltleaf willow opening to forage, while females and young remained in the adjacent untreated feltleaf willow habitat with less forage but more cover [36]. In Denali National Park and Preserve, females with calves tended to use quaking aspen-white spruce and resin birch-diamondleaf willow habitats during the calving-summer period (1 May-24 August) and tended to avoid habitats commonly used by males and females without calves, such as upland Richardson's (Salix richardsonii) or diamondleaf willow habitats [177]. However, in some areas such as southeastern Wyoming, males and females apparently do not segregate [16].

Predation risk: Predators may force moose to select habitats where detection by predators is less probable [75,258]. In a 1996 review, Balsom and others [20] concluded that mature conifer forest may be important to moose because it provides cover, shallower snow depths, and improved mobility, all of which can reduce predation. In southeastern British Columbia, gray wolf moose-kill sites were located farther from edges of small forest patches than random sites (P<0.05 for all variables), indicating that sites farther from cover had greater predation risk [137].

Predation risk may also influence feeding behavior of moose, with moose foraging less selectively with increased predation risk [79]. In Denali National Park and Preserve, moose foraging selectivity on feltleaf willow (based on the stem diameter at the point of browsing) decreased as distance to concealment cover of white spruce forest increased. Cows with calves, which were considered the most vulnerable to predation, fed less efficiently (spent less time foraging and more time alert) than other age and gender classes [180]. In 7- to 10-year-old postfire habitats on the Kenai Peninsula—where vegetation averaged <3 feet (1 m) tall and provided little cover for moose—moose foraged on less preferred species when they were remote from (130-200 feet (40-60 m)) concealment cover in winter [296]. In Michigan, solitary adults and yearlings selected mainland sites with abundant browse, whereas female moose with young calves chose small predator-free islands throughout the growing season even though forage conditions were poorer on the islands than on the mainland sites [75].

In most cases a combination of factors likely influences moose habitat use. In Quebec, moose distribution across the landscape appeared to be a trade-off among predator avoidance, deep snow avoidance, and food availability. At the landscape scale, moose avoided areas used by gray wolf packs, but by doing so, concentrated in areas where snow was deep. However, moose appeared to counterbalance the costs of deep snow by selecting heterogeneous landscapes where habitats providing food were highly interspersed with habitats providing cover [72].

Cover requirements: Calving sites: Calf mobility following parturition is limited, and movements are restricted to the calving site, a small area around the birth site [37]. Maternal females typically remain at calving sites 1 to 2 weeks after birthing [141,240,275], and movements may not approach preparturition levels until 3 to 4 weeks after birthing [37,275]. In south-central Alaska, maternal moose movements increased the 2 days prior to parturition, were greatly reduced for at least the next 9 days, and did not approach preparturition levels until calves were about 26 days old [275]. Moose typically use different calving sites each year ([37,52,297], abstract by [45]).

Moose appear to select calving sites based upon forage abundance and nutritional quality (to support high energetic costs of lactation); vegetation cover and structure (to conceal neonates); reduced predation risk (seeking good vantage points such as elevated open sites from which potential predators could be sighted; areas with reduced chances for encounters with predators; or areas providing escape from potential predators such as areas near open water); or a combination of these factors [3,37,141,215,240,280]. However, calving-site selection is highly variable. Some researchers in interior Alaska [37], central Quebec (abstract by [45]), and south-central Ontario [300] found that calving sites were located at high elevation or locally elevated features such as hill tops or upper slopes, presumably from which potential predators could be sighted; however, elevation and slope position did not appear to influence calving-site selection in northern New Hampshire [240], northwestern Montana, southeastern British Columbia [141], or central Ontario [3]. Researchers in north-central Maine [151], Wyoming (Altmann 1958, 1963 cited in [141]) and northwestern Montana [52] concluded that calving sites were located close to forage and water. In interior Alaska, forage, particularly willow, was more than twice as abundant, and forage quality was slightly but significantly higher, at calving sites than at random sites (P<0.01 for all variables) [37]. However, researchers in northern New Hampshire [240], central Quebec (abstract by [45]), central Ontario [3], northwestern Montana, and southwestern British Columbia [141] found no indication of selection for water or forage.

Several researchers attributed high variability in calving site choice to differences in potential predator avoidance strategies and potential compensatory relationships among habitat variables that provide seclusion and cover [3,141,215]. In interior Alaska, Bowyer and others [37] found an inverse relationship between visibility and availability of forage, indicating that moose made trade-offs between risk of predation and food in selecting calving sites. In southeastern British Columbia moose exhibited 2 distinct calving-site selection strategies: 52% of cows calved at high-elevation sites where forage quantity and nutritional quality were low but risk of predation by grizzly bears was also low, and 48% of cows calved at low-elevation sites close to water where forage quantity and nutritional quality were high. Predation risk was also high at low-elevation sites, but moose selected low-elevation sites with relatively greater visibility [215]. Scarpitti and others [240] suggested that lack of a relationship between calving sites and forage abundance in their study was likely due to abundant food resources throughout the study area. The authors speculated that moose populations at the southern limit of the moose's distribution are unlikely to be limited by food resources, whereas moose in northern regions may have restricted food resources prior to parturition [240]. Bubenik [40] suggested that cover and visibility appeared less important on island sites where predators were absent than on mainland sites.

Aquatic habitats: In North America, particularly in eastern and central parts of the moose's range, moose commonly use aquatic habitats such as lakes, ponds, rivers, marshes, bogs, and muskegs [206,280]. Moose use aquatic habitats primarily to feed on sodium-rich aquatic plants (see Diet) [280]. Moose may also use aquatic habitats to drink water, avoid biting insects, thermoregulate, and avoid potential predators [15,86,206,258]. However, some moose populations exhibit little or no use of aquatic habitats [40,206]. Regional differences in moose use of aquatic habitats are in part related to the availability of aquatic habitats and aquatic plants within those habitats [206]. The availability of alternative sodium sources such as lick sites may also influence aquatic habitat use [86]. Through feeding activity, moose can alter density and composition of aquatic vegetation by reducing the availability of preferred aquatic plants, by trampling plants, or by increasing turbidity (see Moose foraging effects) [86,87,200].

  Moose on the Kanuti National Wildlife Refuge. Photo courtesy of Bill Raften, US Fish and Wildlife Service.

Moose may forage in aquatic habitats year-round, but peak use typically occurs during late spring to fall [206]. Moose appear to begin and end use of aquatic habitats earlier in southern parts of the species' distribution [200]. MacCracken (1992 cited in [206]) reported moose use of aquatic plants throughout the year on the Copper River Delta, Alaska, with peak use occurring May through August. In Ontario, moose began feeding on aquatic plants in late May or early June and continued to feed on aquatic plants until mid-October [282]. Peak use of aquatic habitats coincides with peak moose sodium requirements—which peaks during lactation and antler growth in late spring and early summer—and with aquatic plant phenology and growth—which peak in late summer [1,86]. On Isle Royale, American beaver (Castor canadensis) ponds were frozen from November to April and thus were unavailable to moose. After spring thaw, little aquatic foliage persisted from the previous growing season, so aquatic plants were largely unavailable to moose in spring. Moose ate aquatic foliage as soon as it became available in early June and continued throughout the summer and early fall; maximum aquatic plant biomass was available to moose during late August to early September [5].

Moose select aquatic habitats where their preferred forage is abundant. In east-central Ontario, moose tended to feed in areas with abundant needle spikerush, narrowleaf bur-reed (Sparganium angustifolium), green algae (Chara spp.), Farwell's watermilfoil (Myriophyllum farwellii), and Robbins' pondweed (Potamogeton robbinsii). Moose fed primarily on these species where water flowed into the lake. The water inflow may have supplied hydrogen carbonate and calcium or increased the growth of plants favored by moose [86]. In northeastern Minnesota, American beaver ponds, slow streams, and small lakes with "mucky" bottoms had greater productivity of aquatic plants important to moose than fast streams and large lakes with rocky bottoms. The authors found that only the littoral zone (depth to <10 feet (3 m)) of large water bodies provided aquatic forage plants for moose. American beaver ponds were important sources of aquatic vegetation for moose, but aquatic plant productivity in American beaver ponds varied with pond age, with very young and very old ponds appearing least productive and thus least suitable for moose [1]. Moose on Isle Royale foraged in American beaver ponds dominated by smooth stonewort (Nitella flexilis) and pondweeds (alpine pondweed (Potamogeton alpinus) and small pondweed (P. pusillus)) where water was <4.9 feet (1.5 m) deep and substrates ranged from fine gravel to deep (<3.3 feet (1 m)) silt [5].

Lick sites: Mineral licks used by moose may occur naturally or be man-made. Some researchers consider licks critical to moose health, whereas lick absence in some locations with moose suggests that licks may not be essential on all sites [40]. Moose may use lick sites for water, mineral supplementation, and social gathering [228]. Consumption of lick water and soils may allow moose to improve rumen function and nutrient absorption during transition from low-quality, high-fiber winter diets to high-quality spring forage; to shift from high-quality spring forage to summer forage with higher concentrations of plant defense compounds; to improve palatability and digestibility of forage by absorbing tannins and toxins; to replace mineral reserves depleted during winter; and to supplement elemental intake during molt, antler growth, and nutritional stress associated with pregnancy and lactation [15,264].

Moose use licks throughout the day and night, but primarily from dusk until dawn [15,228,264]. Moose may use licks throughout the year [228,232] but use typically peaks in late spring and early summer before decreasing steadily through the end of summer. Peak lick use coincides with moose calving, molting, and antler growth. Because moose mostly visit licks before aquatic vegetation is fully developed, licks may fulfill moose's sodium requirements before other sodium sources are available [15,144,232,264]. Although moose use mineral licks more often in spring and early summer and aquatic vegetation more in summer and fall, moose visit licks regardless of availability of aquatic vegetation [149,175,232]. This may be because licks provide a more concentrated source of sodium [175,232].

Some researchers found that more females than males visited licks [15,149,175]. Miller and Litvaitus [175] proposed that greater frequency of visits to licks by females in northern New Hampshire may reflect females' greater need for sodium. In Alaska, peak lick use by bulls occurred earlier in the summer than peak use by cows. Summer molt was initiated first by adult bulls and then by cows (see Physical description) and may explain why bulls used licks earlier in the season than cows. Parturition, which confines cows and their calves to calving sites, may also delay lick use by females [264].

FOOD HABITS:
Moose select a diversity of woody species depending upon availability, but most commonly consume willow, aspen, and birch. Moose diet depends on the quality and availability of preferred forage. Moose foraging activity affects plant communities by altering patterns of plant composition and structure (see Moose foraging effects).

Diet: Moose are generalist browsers [231]. They eat the leaves, stems, buds, and bark of hardwoods and some conifers [79,200]. Although about 90% of the annual diet is browse, moose also consume grasses (8%) and forbs (2%) [200,231]. Moose may consume fallen broadleaf tree leaves during the dormant season [79,231]. Moose also occasionally consume lichens, mosses, and mushrooms [231]. Moose strip bark from trees and shrubs for feeding during winter and early spring [79]. Bark stripping is often associated with winter malnutrition [16,231].

Moose consume >220 plant species and/or genera [79,231]. However, at a given location, individuals usually eat high quantities of only a few species [231]. Most studies indicate that >90% of the diet contains <7 different plant species [244]. For example, on the Kenai Peninsula, moose consumed 23 species during winter, but 96% of the total winter diet was paper birch, willow, quaking aspen, and mountain cranberry (Vaccinium vitis-idaea) [229]. In Denali National Park and Preserve, willows accounted for >94% of the biomass consumed by moose [233].

Foods selected vary regionally and seasonally but are generally shade-intolerant, early-successional woody plants [82]. In North America, willow (28 species), birch (paper birch, water birch, dwarf birch, bog birch, Kenai birch (B. kenaica), and yellow birch), and Populus spp. (quaking aspen, balsam poplar, black cottonwood, and bigtooth aspen (Populus grandidentata)) are the principal forage genera [79,93,200,231]. Other important hardwood genera include maple (Acer spp.), dogwood (Cornus spp.), serviceberry (Amelanchier spp.), mountain ash (Sorbus spp.), cherry (Prunus spp.), hazelnut (Corylus spp.), viburnum (Viburnum spp.), and alder (Alnus spp.). Conifers commonly consumed by moose in North America, particularly in winter, include balsam fir, subalpine fir, Canada yew (Taxus canadensis), and Pacific yew [93,200,231]. For a comprehensive list of plants consumed by moose, see Renecker and Schwartz [231].

During the dormant season, moose in northeastern North America consume large amounts of conifers, particularly balsam fir [79,200]. Moose in north-central North America consume mostly hardwoods but also consume balsam fir during winter [79]. Although balsam fir is often an important component of winter moose diets, it is generally not preferred. Moose frequently increase use of conifers such as balsam fir in areas where hardwood availability or quality is low but avoid conifers where hardwood browse is available [188,200,226]. Peek [200] stated that in northeastern Minnesota, red-osier dogwood (Cornus sericea) remained important in the diet for a longer period during a mild winter than during a severe winter, whereas balsam fir and beaked hazelnut (Corylus cornuta subsp. cornuta) became important food items in the diet relatively later during a mild winter than during a severe winter. Along a 30-mile (50 km) segment of the Flathead River in Montana, moose tended to substitute conifer browse for hardwood browse during a severe winter; they consumed 47% conifers and 53% hardwoods during a severe winter and 21% conifers and 79% hardwoods during a mild winter [118].

Moose typically browse plants <8 feet (2.5 m) tall but may browse taller plants where snow supports their weight [147,268]. In areas with trees above browseline, windfallen trees and tree branches provide important food sources in winter [52,234]. On Isle Royale during a year with abundant wind-thrown balsam fir and paper birch (5.1 windfalls/km), 16% of the total biomass consumed by moose was from windfallen trees. The following year, when fewer windfallen trees were available (2.4 windfalls/km), 4% of the total biomass consumed was from windfallen trees [234]. Costain [52] considered seed tree cuts better for moose than clearcuts in northwestern Montana because fallen branches from seed trees, particularly western larch, provided food for moose in winter and early spring.

In spring and summer, herbaceous plants such as grasses (Poaceae), sedges (Cyperaceae), and aquatic plants may be important in the moose's diet [82,200]. Herbs may occasionally constitute >70% of the summer diet (e.g., [130]). Use of herbs may continue into winter if snow is shallow. In Alaska, moose fed on sedges (Carex spp.) in winter when snow was <12 inches (30 cm) deep [200]. In summer , fireweed (Chamerion angustifolium) was heavily consumed in burned areas on the Kenai Peninsula [229].

Moose often consume aquatic plants where available [79]. According reviews, aquatic genera important to moose in North America include pondweed (Potamogeton spp.), horsetail (Equisetum spp.), pond-lily (Nuphar spp.), water lily (Nymphaea spp.), bur-reed (Sparganium spp.), and cattail (Typha spp.) [200,231]. Moose are able swimmers [40] and may feed in water with the entire body submerged [40]. Peterson [210] observed moose diving for aquatic plants >18 feet (5.5 m) deep. Aquatic vegetation provides high protein and sodium content. Moose may consume aquatic plants during spring and summer to replenish nutrient and mineral reserves depleted in winter and to meet requirements for lactation [79,280]. However, moose may also forage on aquatic plants because they are abundant in some areas or because they are more digestible than many terrestrial species [79,93,164]. Some moose do not consume aquatic plants. Moose that occupy areas without access to aquatic plants principally feed on woody vegetation such as willows, which also are high in sodium. Moose may also obtain sodium from mineral licks, especially in spring and early summer [79]. For more information, see Aquatic habitats.

Nutrition and energetics: Seasonal cycles of forage quality reduce moose food intake in winter compared to summer [206]. During summer, moose consume large quantities of highly digestible leaves and aquatic plant parts. Because this material is easily digested, their resting-feeding cycle is short, food intake is generally high, and body fat stores increase. During winter, when moose consume a diet of coarse, poor quality woody vegetation, the resting-feeding cycle is long, food intake is generally low, and body fat stores decrease [231]. Moose reduce their intake of forage in winter even when provided with abundant, high-quality foods [244]. Low forage quality and low food intake in winter result in a diet that is generally insufficient to meet maintenance requirements [249]. This, coupled with increased energy expended by moose traveling through deep snow or digging through snow to get to forage, may result in substantial loss of body fat in winter [280]. Decreased intake results in a lower metabolic rate and reduced activity in winter. Moose store large quantities of fat during summer and fall, which help offset their winter energy deficit [244]. For information on seasonal body size dynamics, see Physical description.

Forage site selection: Moose forage-site selection is based in part on forage quantity and nutritional quality, which is influenced by plant species composition and age, plant phenology and resultant changes in nutrition, site characteristics (soil characteristics, shade, and topography), successional stage, browsing pressure, and weather. Moose forage site selection is also affected by predation risk and proximity of the foraging site to habitats providing cover [231,249,265].

Plant age and parts: Moose preferentially consume young plants and plant parts when they are available [82,231]. These have higher nutrition than old plants and plant parts [192,229,244]. A study of moose browse in boreal forest in central British Columbia found that 1-year-old California hazelnut (Corylus cornuta var. californica) stems had more crude protein (190%) and less crude fiber (56%) than 3-year-old stems in March, and 1-year-old upland willow (Scouler willow (Salix scouleriana) and Bebb willow (S. bebbiana)) stems had more crude protein (126%) and less crude fiber (82%) than 2-year-old stems in February [56]. Houston [109] noted that 18-month-old blueberry willow stems (a "key" forage plant) in Wyoming had less protein and more crude fiber than 6-month-old stems. Protein content in forage often increases the first year or 2 after a fire, but decreases thereafter (see Successional changes in browse).

Moose prefer green deciduous leaves when available. On the Kenai Peninsula, little woody material was eaten while leaves were available on plants. During the dormant season when leaves were unavailable, the current year's growth of woody stems was preferentially consumed over older stems [229]. Moose prefer small-diameter over large-diameter woody stems [79,231]. Large-diameter woody stems are less nutritious and digestible than small-diameter stems [249]. Moose may browse large-diameter stems if more nutritious foods are unavailable [231]. At high densities or when moose are confined to a winter range for long periods by deep snow, browse diameter and utilization increase, bark stripping becomes more common, and diet quality declines [244]. Heavy moose browsing pressure can reduce browse quality, productivity, and species richness locally and thus reduce overall moose diet quality [231,249]. According to a review, in high-quality food patches in summer, moose browse many available stems and then move to another food patch. They often return to the same food patches during winter and browse the previously uneaten stems. They rarely rebrowse stems where the current annual growth has been previously removed unless the food supply is severely limited [231]. In low-quality food patches in winter, moose tend to rebrowse the same woody plants each year [34,35,231]. For more information, see Moose foraging effects.

Seasonal changes in browse: In summer and for much of winter, moose tend to select habitats that offer the highest density, highest biomass, and most nutritious foods [280]. Because these plant qualities change seasonally, moose habitat use also changes seasonally. In general, large amounts of high-quality foods are available in summer; in winter, food is of poor quality and limited in abundance and availability [244,249]. Spring and summer foods of moose are generally 1.5 to 3 times more nutritious than winter foods [229,231,249]. On the Kenai Peninsula the nutritional quality (digestibility and crude protein content) of preferred moose forage species sampled during 6 periods was highest in mid-June and mid-August compared to February, early April, early October, and December [229]. The nutrient content of plants tends to remain high for longer periods during cool, wet summers compared with hot, dry summers [249].

Forage quality is lowest in all habitats in winter, and moose food intake is concurrently low (see Nutrition and energetics) [206]. In a review of moose feeding behavior, Renecker and Schwartz [231] concluded that moose travel less and consume readily available food in winter because all food in winter is of relatively poor quality [231]. However, in east-central Quebec, moose home range size (R²=0.36; P=0.09) and movement rates (R²=0.47; P=0.08) decreased in winter as the proportion of food-rich habitat in their home ranges increased, but such relationships were not significant in summer [70]. In winter, deep and/or crusted snow may also limit options for obtaining food by burying browse and restricting moose to using browse above the snow [200,231,296]. Deep snow may also minimize moose activity and cause moose to shift to habitats with canopy cover to conserve energy (see Cover) [206]. Plant nutrient quality begins to rise in early spring prior to green-up when stored nutrients are transported from roots to buds and twigs [249]. New green vegetation in spring has high protein content that replenishes weight lost by moose during winter [280]. Beginning in spring and throughout early summer, moose increase activity and shift to habitats with the most abundant forage [206,280]. In spring, shrublands and aquatic habitats provide abundant new growth. As summer progresses, moose shift to plant communities that produce new growth later, such as mature birch or aspen forests [206]. In fall in preparation for dormancy, soluble nutrients in plants are transported back to the root system. Leaves die and fall off; conifer needles remain on the tree, but they are generally defended with plant secondary compounds that deter foraging moose. After leaf drop in fall, deciduous browse remains low in nutritive quality throughout the late fall and winter [249]. During spring and fall, forage quality and quantity differ markedly between vegetation types more than during other seasons because some plants begin to turn green sooner or remain more nutritious longer than others [231].

Although forage quality is generally lower in winter than summer, seasonal nutrient dynamics are unique for each plant species. On the Kenai Peninsula in summer, alder and willow ranked the "best" moose browse plants and mountain cranberry the "poorest", but in winter, quaking aspen and mountain cranberry ranked the best and paper birch the poorest. Because different browse species provided moose with different nutrients at different times of year, a variety of browse species best meet the nutritional needs of moose [193].

Successional changes in browse: The quantity and nutritional quality of preferred forage species may fluctuate due to the stage of forest succession and the cause of disturbance [229,244]. Typically, both quantity and nutritional quality of moose browse increase after fire and other disturbance and decline as forests mature, but successional dynamics are unique for each browse species [56]. For information on effects of fire and other disturbance on moose browse species, see FEIS reviews on species of interest.

Forage nutritive quality often increases after fire [161]. The effect of burning on nutritive quality of moose browse may last up to 20 years [161] but is often short term, lasting <2 years. Following the Rosie Creek Fire, a stand-replacing May wildfire in boreal forest in interior Alaska, crude protein and phosphorus, calcium, magnesium, and potassium content of moose browse species (quaking aspen, paper birch, and willow) were highest the 1st growing season after the fire and declined significantly in postfire year 2 (P<0.05) [165]. A study in northern Idaho western redcedar/Oregon boxwood (Thuja plicata/Paxistima myrsinites) habitat found that spring prescribed burning increased crude protein content of moose browse (willow and Saskatoon serviceberry (Amelanchier alnifolia)) during postfire year 1, but the effect was absent during postfire years 2 and 3. Digestibility of moose browse increased after the fire, and the effect lasted through postfire year 3, when the study ended [13]. In Chugach National Forest in the Kenai Mountains, protein content of moose browse (e.g., paper birch, quaking aspen, Scouler willow, and Barclay's willow) in Sitka spruce-hardwood forest was significantly higher on sites burned under prescription than on nearby control sites during postfire year 1 (P<0.05), but no such differences were found between burned and control sites 2 to 24 years after burning [295]. In eastern Maine, digestible energy of moose forage available on 15- to 17-year-old plots burned in a wildfire was substantially lower than digestible energy of moose forage on 3- to 4-year-old plots burned under prescription [57].

Nutritive quality may also increase after logging or mechanical treatment. On Newfoundland sites where moose populations varied from low to high, moose fed preferentially on thinned balsam fir stands (about 2,000 balsam fir stems/ha) compared to unthinned stands (about 30,000 stems/ha). Thinned stands were 10 to 12 years old and cut 2 years prior to the study. Moose apparently preferred the more nutritious (greater digestibility, higher protein content) balsam fir twigs in thinned stands [278,279].

Many moose browse species (e.g., paper birch, quaking aspen, willow, and balsam poplar) increase in abundance after disturbance [50]. Forage, particularly willow and quaking aspen sprouts, increased after a spring (March-April), low-intensity prescribed fire in a ponderosa pine/Douglas-fir stand in Montana. The stand had been thinned from below, selectively cut, and slash-pile burned prior to the prescribed fire [12]. In the boreal forest region of north-central Newfoundland, available moose winter browse (primarily balsam fir) increased 10-fold from postclearcut year 2 (180 pounds/acre (200 kg/ha)) to post clearcut year 8 (1,800 pounds/acre (2,000 kg/ha)), at which time it peaked and subsequently declined sharply. Moose used 8- to 15-year-old clearcuts most. The authors concluded that the "most valuable" clearcut areas for moose were 8 to 10 years old [195]. In a southwestern Alberta quaking aspen forest, moose browse production the second year after clearcutting and burning under prescription was 55% greater than in uncut stands; during postclearcut year 7, browse production declined compared to postclearcut year 2 but was still 52% greater than in uncut stands [270]. Mechanical crushing of feltleaf willow in interior Alaska in 660- to 2,620-foot (200-800 m) wide strips increased moose forage abundance 3 years later compared to an uncrushed site [36]. An 8.2-mile² (21.2 km²) May stand-replacing wildfire in boreal forest in northwestern Ontario killed most trees, mostly black spruce and jack pine. Ground cover and aboveground parts of shrubs were mostly consumed. Plant growth began soon after the fire. By mid-July, ground cover exceeded that in unburned areas. In the second growing season after the fire, shrubs were observed on the burn. By the 5th growing season, mean height of hardwoods was about 7 feet (2 m). Thus, moose browse was eliminated on the severely burned areas for 2 years, became available in small amounts during postfire year 3, and was abundant by the 5th postfire year [60].

Early-seral forests often contain a greater variety, quantity, and quality of moose forage than mature forests [135]. On burns on the Kenai Peninsula, density and biomass of paper birch, willow, and quaking aspen 3 to >90 years after fire was highest in burns that were 8 to 30 years old [194]. In interior Alaska, quaking aspen browse was most abundant 1 to 5 years after fire, and birch and willow browse was most abundant 10 to 16 years after fire [301]. In boreal forest in central British Columbia, protein content generally decreased and crude fiber content generally increased in moose forage species with forest age. Available browse was 3.0 times more abundant in young (6 years old) quaking aspen-willow forest than old (>70 years old) Engelmann spruce forest, and intermediate-aged (20-30 years old) lodgepole pine forest had 1.7 times more available browse than old Engelmann spruce forest. Fats, carbohydrates, and proteins in moose browse were highest in young and intermediate-aged forests and lowest in old forests. However, carotene and possibly mineral content in moose browse increased with forest age. The authors concluded that the "most desirable" winter range for moose has a variety of palatable species in a range of age classes, but primarily in young forests [56].

The response of individual moose browse species to fire and other disturbance is determined by the species' structural and physiological adaptations to fire and life history characteristics [4]. Slashing (complete overstory removal) and early-spring (prior to plant growth) prescribed fire were applied to 40 acres (16 ha) of moose winter range in mature quaking aspen-Engelmann spruce forest, Douglas-fir/mallow ninebark (Physocarpus malvaceus) forest, and hawthorn (Crataegus spp.) shrublands in the West Boulder River drainage in the Absaroka Mountain range in south-central Montana. Saskatoon serviceberry and chokecherry were prominent understory shrubs and important moose browse species. Two years after the fire, density of quaking aspen and willows had increased due to sprouting. Prior to treatment, quaking aspen was too tall for moose to reach; after treatment, quaking aspen was low and could be utilized. However, Saskatoon serviceberry and chokecherry were reduced compared to prefire levels [97]. On the Chugach National Forest, moose winter browse species (quaking aspen, paper birch, black cottonwood, balsam poplar, and willows) in Sitka spruce-hardwood forest generally increased in abundance 15 to 20 years after burning under prescription in May and June compared to prefire levels. Early-successional herbaceous plants consumed by moose such as fireweed also increased. Late-successional species, conifers, and some moose browse plants, including mountain cranberry, decreased in abundance by 15 to 20 years after burning compared to prefire levels [33,295].

Moose forage species may respond to disturbance in different ways depending on season and type of disturbance. Quaking aspen may sprout more readily and form denser stands from winter cutting than from summer cutting [200]. In northeastern Minnesota, Peek and others [201] found higher crude protein content in 6 moose forage species in areas burned by a "hot" wildfire than in areas burned by a "cooler" prescribed fire. On the Kenai Peninsula, production of forage in a young burn (10 years old) that resulted from a "hot" wildfire was 5 to 8 times greater than that in an old burn (32 years old) that resulted from a "cooler" wildfire. Moose forage plants growing in the young burn had 2% to 3% higher crude protein content during spring and summer than that in the old burn, a result attributed to the old age of shrubs, heavy browsing pressure, and closed spruce canopy in the old burn. However, nutritional quality of moose forage was not different between the 2 burns in fall and winter [229]. Moose twinning rate was 3 times higher [84] and moose density 3 to 4 times greater in the young burn than the old burn [229]. Greater quantity of winter forage in combination with greater quantity and/or higher nutritive value of summer forage may have resulted in greater moose productivity on the young burn compared with the old burn (see the Kenai Peninsula case study) [229].

Moose browse is typically most available in early-successional habitats and declines in midsuccession. As a stand progresses through midsuccession into late succession, however, browse availability may again increase as trees die and the canopy breaks up. In the Susitna River floodplain, Alaska, early-successional feltleaf willow (<14 years old) communities and late-successional (>50 years old) balsam poplar forests were important wintering habitats for moose. Browse availability was the principal factor affecting winter habitat selection by moose. Feltleaf willow was the dominant browse species, constituting 92% of available browse and 96% of browse consumed by moose. Available browse was low in midsuccessional forests due to the combined effects of canopy closure shading out browse and browse growing beyond the reach of moose. When sites were approximately 50 years old and the canopy broke up as a result of tree mortality, browse availability increased. Highbush cranberry (Viburnum edule) and prickly rose (Rosa acicularis) were abundant moose browse species in late-successional balsam poplar forest [49]. Moose populations in the Jackson Hole region, Wyoming, increased over 50 years as successional vegetation advanced because of increased subalpine fir, which is a staple food for moose in this region [156]. In Alberta, moose used >120-year-old stands, apparently exploiting vegetation growing in canopy gaps (Stelfox and others 1995 cited in [80]). In north-central Idaho, moose preferentially foraged on Pacific yew in the understory of multicanopied, old-growth mixed-conifer forest [208,213].

Moose foraging effects: Moose can affect the successional trajectory and rate of succession of habitats they occupy [43,79,121,197,199]. They can influence plant species composition and diversity by consuming palatable species and allowing unpalatable species to gain dominance (e.g., [9,26,44,87,193,214,277]). They can alter forest structure by preventing saplings of preferred species from growing into the tree canopy, resulting in a forest with an open tree canopy and a well-developed shrub and herb understory (e.g., [23,27,126,158,171]). They can influence rates of nutrient cycling by altering litter quantity and quality and via urination and defecation (e.g., [121,171,196]). Also, moose may affect growth of stems and leaves and alter levels of plant nutrition (e.g., [26,181,254]). According to reviews, the effect of moose browsing depends upon moose density and population dynamics and resultant duration and frequency of feeding activity by moose; the presence or absence of predators; initial plant species richness, composition, and age; and season of browsing [79,94]. In aquatic habitats, moose foraging effects may also depend upon water levels that control plant phenological development [87,200]. The size of a disturbance may influence the effect moose foraging has on a stand. LeResche and others [154] suggested that moose in most cases do not alter the successional trajectory in large burned areas, but that the course of succession may be altered in small burned areas that receive heavy browsing pressure, particularly if other early-seral habitats are sparse. Lutz [159] suggested in 1956 that the 1947 wildfire on the Kenai Peninsula (see Kenai Peninsula case study) would likely not provide long-term moose browse in part because of "the failure of willows to appear in numbers sufficient to withstand heavy use, and the fact that most of the browse is aspen sucker growth, which does not successfully withstand heavy browsing". See these sources for more information on this topic: [62,79,121,199].

Moose may be indirectly affected by herbivory by other ungulates, American beavers, and snowshoe hares (Lepus americanus). For a review of how herbivory by these species affects boreal forests in general and moose in particular, see Pastor and Naiman [198]. For a review of interrelationships between moose and other wildlife species, see the review by Boer [32].

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
Information on state- and province-level protection status of animals in the United States and Canada is available at NatureServe, although recent changes in status may not be included.

MANAGEMENT CONSIDERATIONS:
Status and threats: Within the past 100 years, particularly since the 1950s, habitat and harvest management to create early-successional habitat and translocation practices in many areas have enabled moose populations to expand. In other areas, particularly on the southern edge of moose's distribution in eastern and central North America, development and agriculture have reduced moose numbers and distribution. Global climate change may have contributed to constriction of moose range from parts of its southern distribution and is predicted to cause further shifts northward [123].

Range expansion and contraction: Moose have expanded their distribution throughout much of North America since the early to mid-1800s. Absent in interior British Columbia before 1860, moose are now present throughout British Columbia. Since the 1800s, but largely in the 20th century, moose have expanded their range south to parts of the southern Rocky Mountains and spread into new areas of Washington, Oregon, Montana, Wyoming, Colorado, and Utah [123]. According to Surber and others (1945 cited in [210]), moose populations increased as a result of increased habitat created by fires in Minnesota in the late 1800s. In Quebec in the 19th century, fires and logging seem to have been the main factors responsible for the rapid growth of moose populations (Joyal 1976 cited in [223]). In the 20th century, moose expanded their range to Isle Royale in Lake Superior, to areas north and east of Lake Superior in northern Ontario and northern Quebec, to areas in southeastern and northwestern Alaska [123,265], and northeast into the Northwest Territories and Nunavut [129,190]. Moose were introduced into Labrador and Newfoundland by humans in the early 20th century [265]. Moose have also expanded into the transition zone between prairie and boreal forest in Alberta, Saskatchewan, and Manitoba, expanding progressively farther south into the prairie edge [123]. Much of the range expansion has been attributed to the postglacial dispersal that is "still in progress"; to protection from overhunting; to declines in large predator populations; to human translocations; to climate change; and to increased logging and fire that created large tracts of habitat suitable to moose [93,123,129,190,280].

Conversely, moose range has contracted in some areas, such as in southern New England—where development has reduced habitat suitability—and in northwestern Minnesota—where agriculture has reduced suitable habitat [123]. Murray and others [184] concluded that climate change, acting in tandem with pathogens and malnutrition, was responsible for the decline in moose populations in northern Minnesota since the mid-1980s. Karns [123] surmised that fire exclusion and road development in New Brunswick since the 1920s reduced fire frequency and size and subsequently reduced available habitat for moose. Historically, moose occurred in southern parts of Ontario, Michigan, Pennsylvania, New York, and New England, but were extirpated from these areas in the late 1700s to early 1900s. Karns [123] noted in 2007 that moose populations appeared to be expanding back to the southern parts of these regions. However, climate change is predicted to restrict further moose population growth to the south.

Climate change: Moose are sensitive to heat stress (see Physiology), and moose survival may be heavily influenced by high snow accumulations (see Survival). Thus, moose are potentially affected by large-scale climatic fluctuations such as the North Atlantic Oscillation (NAO) that influence local temperature and precipitation patterns [219,257]. The NAO accounts for much of the interannual variation in wintertime temperature and precipitation in the northern hemisphere and exhibits phases of increase and decrease that persist over decades [219]. Researchers reported correlations between moose abundance and the NAO on Isle Royale that suggested increased snow depths resulting from the NAO led to high moose mortality and low recruitment and ultimately reduced moose densities 1 to 3 years later [121,218,219].

The effect of climate change on moose is unresolved and predictions are conflicting. Because certain periods of the NAO produce regional climate effects that resemble the predicted effects of rising carbon dioxide, correlations between moose abundance and the NAO may help predict moose's response to global climate change. Based on this premise, rising carbon dioxide resulting in warmer winters and decreased snow depth may benefit moose, causing a cascade of effects including rising moose populations and forest structure changes due to increased moose browsing [241]. In contrast, Lenarz and others [150] used models based on January temperatures and late spring temperatures in northern Minnesota to explain variability in survival rates. Their results suggested that increased winter and late spring temperatures may be detrimental to moose due to heat stress. Murray and others [184] reported that during the late 1900s, annual moose population growth rate was related negatively to mean summer temperature. This suggested that current and predicted climate change trends may decrease survival and population density, and ultimately cause a retreat of moose northward from their current distribution [150]. Because local losses of moose are predicted to be compensated by moose range expansion into new geographic locations, climate change models comparing current and predicted geographical distributions under doubled carbon dioxide levels predict that moose will remain in most of their current geographic range [241]. Changes in global temperature regimes may result in spread of disease and parasites that affect moose or result in increased incidence of diseases that reduce moose productivity or increase mortality [150]. Climate change may also affect forest insect, pathogen, and fire cycles that alter forest structure and thus moose populations [266]. Interior Alaska is predicted to experience increased temperatures and decreased precipitation with continued global climate change. These changes are predicted to alter the fire regime, specifically leading to larger and more severe fires. This has the potential to increase moose foraging habitat over large areas [158]. Ultimately, climate change is likely to influence moose numbers and distribution indirectly through a range of complex ecosystem-level changes [150].

Succession: Moose consume early-seral woody vegetation resulting from disturbances such as fire, flooding, forest insects and diseases, windthrow, avalanches, landslides, ice scour, glacial action, and logging [82,93,265]. Mature forests provide important moose cover, particularly in regions with high snowpacks [93]. Several researchers and reviewers ranked moose habitats along a continuum from "stable" to "unstable" in the long term (e.g., [154,206,265,289,289]). Stable moose habitats persist through time and included large alluvial floodplains and deltas and small stream valley shrublands. Moose forage is maintained for long periods in these habitats by frequent flooding, scouring, erosion, and deposition [206]. Fire was historically rare in these communities [117]. In the Susitna River floodplain in Alaska, the availability of early-successional floodplain habitat to moose was constant during a 14-year period [49]. Tundra and subalpine shrublands were also characterized as stable moose habitats [206]. Fire was historically rare in these habitats as well [288]. When fire occurs, postfire succession of dominant life forms progresses from grasses, forbs, and mosses to shrubs that were present before fire [42].

Unstable moose habitats, such as some boreal and mixed-transitional forests, are seral forest types that succeed from hardwoods to conifers after disturbance. Disturbances such as fire and insect outbreaks (e.g., eastern spruce budworm (Choristoneura fumiferana), mountain pine beetle (Dendroctonus ponderosae), and spruce beetle (Dendroctonus rufipennis)) were historically frequent in these habitats [79,206,265]. Sprouting deciduous woody plants and plants with wind-disseminated seeds (e.g., quaking aspen, birch, and willow) typically increase after disturbance that opens the canopy [194]. As succession proceeds, often within 5 to 10 years, hardwood shrubs and saplings grow above the snow and become accessible to moose in winter. Postdisturbance boreal forest may provide high-quality habitat for moose at this time and moose densities often increase. As stands age, hardwoods eventually grow out of reach of moose and are slowly replaced by spruce and other unpalatable conifers, but this process may take over 100 years [194]. Moose populations decline as hardwood stem availability declines, most often within 10 to 30 years [157,186,247,250,296]. Timing of moose population decline depends on the type of disturbance and resultant rate of vegetation change.

Geist (1971,1974a cited in [206]) hypothesized that moose populations find refuge in stable habitat found along watercourses and deltas and in high-elevation shrub communities, but they expand into unstable habitat when disturbance creates abundant food. Telfer [266] modeled moose browse yield for 4 fire cycles (38, 50, 75, and 100 years) representative of historic fire cycles in boreal forest. He found that total moose browse production decreased as fire cycles lengthened, and as fire cycles lengthened, the importance of muskeg and riparian areas to moose assumed relatively greater importance [266].

Postfire succession: For information on postfire succession, see Postfire vegetation changes and succession.

Postlogging succession: Logging can create early-successional habitat favorable to moose. Researchers reported that the benefits of forest harvesting for moose peak within 30 years following logging (e.g., [54,56,79,81,84,169,182,188,221]). In a central Labrador boreal forest in winter, moose browsed most frequently on willow and paper birch in 20- to 30-year-old clearcuts. Little to no moose browsing occurred in young clearcuts (5-10 years old) and mature forest (>150 years old) [188]. In a long-term study in strip-clearcut white spruce forest of central Alberta, moose use of the stripcuts was low during the first 5 years after cutting. Uncut strips were logged 12 years after the initial cutting. During summer, moose use of the clearcuts increased as forage density and height increased. Nine years after clearcutting, moose density was 2 moose/mile²; 17 years after clearcutting, moose density was 3 moose/mile² [256]. A subsequent study reported that moose did not use the clearcuts during winter until 20 to 25 years after logging, when white spruce were tall enough in the clearcuts to provide cover (Stelfox 1981 cited in [280]).

Clearcuts may be detrimental to moose populations in the short term until browse and/or cover increase [54,74,136,169,220]. Reduction of forage and cover and increased moose mortality caused by hunting and predation following logging were suggested to explain low moose densities in recent clearcuts [73,74,220]. Potvin and others [222] examined moose use of study sites 2 years before and 2 years after clearcutting patches of 250 to 620 acres (100-250 ha) in 20- to 44-mile² (52-114 km²) blocks separated by 200- to 330-foot (60-100 m) wide buffer strips in conifer-hardwood and mixed-conifer stands of black spruce, jack pine, balsam fir, paper birch, and quaking aspen in western Quebec. Because moose avoided open areas with sparse shrubs, moose density decreased 20% to 30% following clearcutting. Moose usually kept the same home range but preferentially used uncut parts, avoiding clearcut patches in their home range. By postclearcut year 10, however, available browse in the clearcuts was greater than that in uncut stands, and moose densities increased 54% to 87% compared with densities immediately after the cuts, a result attributed to restricted hunting but also to vegetation growth following clearcutting [220].

Logging may reduce moose food and cover for long periods in late-successional habitats. In north-central Idaho in winter, Shiras moose fed on Pacific yew in old-growth (>90 years old) grand fir/Pacific yew forests [208]. Pierce and Peek [213] recommended that timber harvest be avoided in such stands because clearcutting and prescribed fire were likely to substantially reduce moose forage for long periods. In North Park, Colorado, encroachment of subalpine fir—an important winter browse species during periods of deep snow—seemed to increase moose preference for quaking aspen stands. The author hypothesized that treatments that removed subalpine fir from aspen stands were likely to create less suitable habitats for moose [16]. In dry, interior Douglas-fir forest in British Columbia, deep snow in logged areas of the forests apparently impeded moose movements, so uncut forest reportedly had the highest winter use and provided the best winter habitat for moose [110].

Bluejoint reedgrass (Calamagrostis canadensis) readily colonizes logged areas in boreal forests, making conditions less favorable for germination and establishment of hardwoods used by moose. A study that examined 96 logged sites in southeastern Alaska found that hardwood exclusion by bluejoint reedgrass was especially evident in stands cut during the dormant season, when the ground was covered by snow and mineral soil was not disturbed [50]. Other researchers reported that fire, logging, or spruce beetle outbreaks in Alaska increased colonization with unpalatable bluejoint reedgrass unless mineral soil was exposed by the disturbance (e.g., [33,50,79,108,154,259]). These studies suggest that logging with soil disturbance favors moose. However, many other factors influence the suitability of habitat for moose following disturbance. For more information on this topic, see Postfire vegetation changes and succession.

Succession following forest insect outbreaks: Eastern spruce budworm infestations—by themselves or in combination with fire—set back plant succession and are genearlly favorable to moose [57,135]. Balsam fir is important to moose in winter, with saplings providing browse and mature stands providing cover [135]. During severe outbreaks of spruce budworm, most of the balsam fir in the canopy may be killed, and many spruce may also be killed [57,253]. This may result in even-aged stand development over extensive areas [57]. Thus, eastern spruce budworm outbreaks may benefit moose by creating openings that favor growth of browse [79,189,206], but they may also be deleterious by removing important winter cover [135]. Vegetation growth following an eastern spruce budworm outbreak in Nova Scotia provided abundant forage for moose [253]. On Isle Royale, although an eastern spruce budworm outbreak killed balsam fir in the overstory, the removal of overstory balsam fir trees increased moose browse production in the long term by increasing balsam fir and shrub growth in the understory [133,135]. In mixed-transitional forest in Algonquin Provincial Park, areas with moderate or severe spruce budworm-caused tree mortality >5 years prior had more moose than areas with low tree mortality. The effect of spruce budworm-caused tree mortality on moose abundance was greater in pine (eastern white, red, and jack pine)-bigtooth aspen-paper birch forest than sugar maple-yellow birch-eastern hemlock forest. This may be because browse availability increased in the conifer type, so food and cover were in close proximity [81]. Death of trees over large tracts of mature forest creates abundant fuels [133], which has led to severe wildfires in spruce budworm-killed stands [57]. In northwestern Ontario, Simkin (1963 cited in [133]) noted that when spruce budworm-killed stands were burned, the succeeding vegetation growth provided excellent moose habitat.

Mountain pine beetle outbreaks may benefit moose by creating openings that favor browse, although extensive and uniform infestations typically reduce the habitat heterogeneity that benefits moose [236]. Koch [131] reported that mountain pine beetle outbreaks and other canopy removal in lodgepole pine forest were likely detrimental to moose because the browse species most prevalent in the moose's diet were found in old lodgepole pine forests rather than in young forests.

Habitat management: Disturbance can create good habitat for moose by favoring browse growth and by creating ecotones between areas of dense cover and more open feeding areas. Conversely, loss of cover over large areas can be detrimental for moose by, for example, increasing homogeneity, increasing the snow cover in open areas, or increasing hunting and/or predation pressure [263]. Retention of mature conifer stands appears particularly important to moose survival where riparian communities are sparse and in deep snow [206]. Feldhamer and others [79] cautioned that habitat management meant to increase moose habitat is unlikely to benefit moose populations limited by high predation, overharvest, or other sources of high mortality. Thompson and Stewart [280] recognized the importance of clearcutting for creating or improving moose habitat by opening forests and allowing for growth of accessible, high-quality browse plants, but emphasized that "merely cutting forest to stimulate regrowth does not constitute habitat management for moose". Instead, resource managers need to consider proximity of food and cover, water, mineral licks, aquatic vegetation, and the effects of hunting and other human disturbances. Because local variations in forage and cover preferences and availability are important, researchers recommended that habitat management favor the locally preferred forage species and habitats [82,200].

Historically, mosaics of unburned, partially burned, and severely burned areas resulting in landscapes in a variety of seral conditions were created by fire, windthrow, and forest insect outbreaks. In some areas, logging has become the major disturbance [206]. Logging and other types of habitat management such as mechanical crushing, prescribed fire, and herbicide application, singularly or in combination, may create seral habitats of value to moose [79,194,280]. In general, overstory removal or clearcutting that increases light to the ground and exposes mineral soil favor establishment of shade-intolerant species such as birch, aspen, and willows, whereas overstory thinning or selection cutting favors growth of shade-tolerant species such as subalpine fir [50,54]. Because moose forage species respond differently to different habitat management practices and because moose benefit from increased habitat heterogeneity, researchers suggested that a variety of habitat management techniques be employed in a given landscape to provide for variety of forage species and diversity of habitats from which moose can choose [52,110]. Costain [52] recommended multiple small clearcuts with seed trees; narrow clearcuts with irregular edge; or numerous "islands" of trees and shrubs within large clearcuts as management strategies for moose in northwestern Montana. All 3 strategies, he surmised, would maximize edge, leave some browse, and provide hiding cover close to foraging habitat. Other researchers recommended retaining residual trees in clearcuts to provide cover patches and seedfall for vegetation reproduction to enhance postclearcut forage growth for wildlife in general [80] and moose in particular [55,169,182].

According to a comprehensive review by Thompson and Stewart [280], moose habitat management objectives include: According to Hundertmark [112], moose management should take into account the fact that migratory and nonmigratory segments of a moose population may exhibit different behavior and have different population demographics. Feldhamer and others [79] suggested that because male and female moose are often segregated in different habitats, they should be managed as if they were separate species. Fire: For information on the use of prescribed fire in moose habitats, see Fire Management Considerations.

Logging: Logging often benefits moose by creating abundant, nutritive browse (see Successional changes in browse) [79,223]. Many moose browse species are well adapted to disturbance, and moose commonly use young clearcuts for foraging, often selecting them over other available habitats [78,226,239]. In general, clearcutting has increased moose populations within 30 years after logging (see Succession) [79]. Several researchers have attributed increased moose distributions throughout North America during the 1900s to clearcutting over vast areas (see Range expansion and contraction) [123]. However, logging can enhance or severely reduce moose habitat quality, depending upon forest management objectives, timing of harvest (dormant or growing season), harvest method, and postlogging site preparation [50]. Postlogging site preparation practices employed in moose habitats include prescribed fire, herbicides, and mechanical treatments [50].

Moose generally avoid large clearcuts and browse is far from concealment cover. Thus, numerous small clearcuts may be more beneficial to moose than a single large clearcut because of increased edge habitat [280]. In winter, moose in northwestern Ontario either preferred or used as available clearcuts with edge habitat provided by 328- to 656-foot (100-200 m) wide strips of uncut forest within the clearcut over clearcut areas without strips, apparently because the edge habitat provided food, thermal cover, escape cover, and better snow conditions [168]. Conversely, near Thunder Bay, Ontario, moose used large clearcut areas more than areas with strip cuts (131-164 feet (40-50 m) wide; P<0.05), apparently because the narrowness of the strip cuts caused deep snow accumulations that made forage less available than in large clearcut areas. However, the authors noted that within the large clearcuts, moose mostly used the area within 98 feet (30 m) of conifer cover. Clearcuts and strip-cut areas were 7 to 14 years old and 334 to 1,310 acres (135-530 ha) in area [284]. Moose in Ontario selected dense conifer edges along islands of residual timber within clearcuts as opposed to edges of large cuts [172]. In north-central Ontario highest moose densities occurred where large blocks (>1.9 miles² (5.0 km²)) of uncut forest were left after clearcutting; intermediate moose densities occurred in areas with medium-sized (≥0.3 mile² (0.7 km²) and <1.9 miles²) blocks of uncut forest; and the lowest moose densities occurred in areas with the smallest blocks (<0.3 mile² (192 acres)) of uncut forest, suggesting that greater amounts of forest cover resulted in higher moose densities in the landscape [74].

Mechanical treatment: Mechanical treatments applied in moose habitats include postharvesting site preparation for conifer planting and crushing browse to stimulate growth. Postharvesting mechanical treatments typically scarify the forest soil, which often benefits hardwood seedling establishment and growth. However, such preparations alter nutrient, moisture, and temperature relationships that could be deleterious to moose browse species. Selection of the "best" method for a given area is influenced by soil fertility, soil moisture, and depths of organic and mineral soil horizons [50]. See Collins and Schwartz [50] for a review and specific management recommendations for scarification in moose habitats in Alaska. Mechanical crushing of willows was used to increase willow growth for moose in several studies. For more information, see these resources: ([36,246], Oldemeyer 1977 cited in [17]).

Herbicide application: Herbicides are sometimes used in spruce-fir forests to promote conifer dominance on clearcut sites by suppressing hardwoods [226]. In general, herbicide use in clearcuts promotes conifer growth and decreases moose hardwood browse availability in the short term (<4 years) (e.g., [78,127,146,148,226,239]). In the long term, it may increase hardwood browse availability by slowing hardwood growth so browse remains accessible longer [189]. However, one long-term study examining moose use of clearcut- and herbicide-treated quaking aspen/highbush cranberry habitat in western Alberta found that herbicide treatment reduced winter browse availability for at least 20 years [261].

Roadway and railway management: Moose-vehicle collisions are substantial sources of moose mortality in some areas. Moose habitually use roads and railways as travel routes between habitats [46,282], and road salts attract moose, thus increasing moose-vehicle collision risks (see Survival). Attempts to mitigate collision mortality have included discouraging moose from rights-of-way, reducing the attractiveness of roadside vegetation and salt pools, and warning drivers [47,79,149,227].

Roadways facilitate access for hunters. Increased road access can lead to higher harvest rates and population declines [79]. Studies in south-central Ontario reported disproportionately high moose harvests associated with increased road access in recently clearcut boreal forests [73,74]. Landscape-level analyses in Ontario covering 19 years suggested that if large-scale forest disturbance such as logging or fire occurs concurrently with hunter access, then moose density decreases across the landscape, but moose density increases if disturbance occurs without hunter access. These results suggested that increasing habitat alone may not increase moose density if hunting is not restricted in those areas [230]. Conversely, researchers in Quebec reported that increased accessibility as a result of new logging road creation had a minor impact on moose harvest rates [53,221].

Water management: Riparian communities maintained by periodic flooding are important moose habitats [49,93,117]. Because flooding helps maintain quality moose habitats, active management of riparian areas is generally not recommended where flooding occurs regularly [49]. Thus, Child [47] recommended that natural flooding regimes be maintained where possible.

Moose often follow forested shorelines until they reach patches of aquatic vegetation [46]. Thus, researchers recommended that forested habitat be maintained along shorelines and stream corridors [46,52,282]. In logged, mixed-transitional forests of central Ontario in summer, moose preferred aquatic feeding areas that were buffered by forested habitat (i.e., "reserves") >390 feet (120 m) wide and adjacent to shorelines with long lengths of aquatic vegetation. Wide reserves around aquatic feeding areas likely provided a diversity of terrestrial and aquatic browse, protective travel corridors, multiple entry points to the water, and improved ability to thermoregulate. Reserve width appeared less important to moose in aquatic feeding site selection when cut areas near water were >10 years old, suggesting that reserve width became less important as the edge between the cut and reserve became less abrupt [46].

Population management: The moose is hunted throughout most of its range [82]. Hunting can alter population density, adult sex ratios, and life span (see Survival). In a comprehensive review, Schwartz [245] suggested that maintaining an adequate bull:cow ratio may help ensure timely breeding and adequate moose population growth. One study of taiga moose in central Quebec found no effect of skewed bull:cow ratios produced by intensive hunting on moose reproduction and population productivity. This was attributed to increased breeding by subadult males and the placement of the main hunting period after the rut. The authors cautioned, however, that long-term effects of skewed adult sex ratios as a result of high hunting pressure were uncertain and that managers should favor sex ratios close to levels in unhunted populations [145].

FIRE EFFECTS AND MANAGEMENT

SPECIES: Alces americanus
DIRECT FIRE EFFECTS:
Fire has killed moose directly [47,88,92,98,99,252]. Large mammal mortality in general is most likely when fire fronts are wide and fast moving, fires are actively crowning, and thick ground smoke occurs [88,252]. In Manitoba, a large, fast-moving fire (312 miles² (809 km²) in 8 hours) killed some moose unable to escape (Crichton personal communication cited in [92]). Necropsies revealed the primary cause of death of moose and other large mammals during the Greater Yellowstone Area fires of 1988 was asphyxiation by smoke inhalation [88].

The number of fatalities caused by fire is likely related to season, moose population density, habitat type, fuel load, availability of escape terrain, and prevailing winds [47]. Spring fires may cause mortality more than fires in other seasons because of limited mobility of young [163]. As of this writing (2010), however, it was unclear whether moose calves were most vulnerable to fire-caused mortality in spring.

Fire-caused mortality rates of large mammals in general are low (<1%). Thus, direct fire-caused mortality is thought to have little effect on large mammal populations [88]. Child [47] agreed that direct fire-caused mortality of moose is generally "insignificant" and that fire-caused mortality is less important to moose populations than the potential for long-term improvements in moose range created by fire (see Indirect Fire Effects).

General observations suggest that moose use areas during and soon after fire. During the Greater Yellowstone Area fires of 1988, moose fed in the vicinity of fire while it burned nearby [88,98]. On the Kenai National Moose Range, south-central Alaska, Hakala and others [99] reported that "at no time were moose observed, either singly or in groups, moving hurriedly out of the path of the approaching fire". Similarly, moose in central Alaska showed no reluctance to use portions of their home ranges within a fire perimeter, even while the fire was burning nearby and producing dense smoke; moose were seen standing within 49 feet (15 m) of small flames [92].

INDIRECT FIRE EFFECTS:
Moose populations respond directly to fire-caused changes in cover and food. In general, the literature regarding fire effects on moose habitats indicates that burning sets back plant development and succession, often increasing moose forage quality and/or forage quantity, and usually increases habitat patchiness, providing moose with abundant edge habitat and diverse vegetation. Moose are most likely to benefit from patchy fire that creates early-successional habitats providing browse while leaving interspersed patches of mature, closed-canopy forests that provide cover. Moose are least likely to benefit from fire that results in large expanses of homogeneous vegetation [63,79,206]. Fire's effects on moose habitats are complex and not thoroughly understood but depend in part upon fire type and the plant communities affected [163]. Most studies are descriptive rather than quantitative, use small sample sizes, are short term, or include no controls and/or replicates, so results presented here should be interpreted with caution.

Moose population response to postfire vegetation changes: In general, moose avoid burned areas until vegetation growth begins. Moose populations increase as postfire communities of aspen, birch, and willow develop and forage becomes more abundant. Moose forage abundance may increase from 1 year to more than 100 years following fire, depending upon fire type and plant communities affected [162]. Although vegetation growth following fire may immediately provide abundant moose browse, "optimal" moose forage in boreal forest typically occurs approximately 10 to 30 years after fire [186], with a peak in forage production and moose population density occurring about 15 years after fire [206]. As stems of maturing aspen, birch, and willow exceed the reach of browsing moose (>8 feet (2.5 m) tall [268]), moose population density declines [206,254]. However, moose use of burned areas varies widely, in part due to variation in postfire vegetation growth rates, adjacent habitat, and prefire moose density and movements [90]. The more rapidly that browse is replaced by unpalatable conifers or grows out of reach, the shorter the productive life of the burn for moose [154].

Moose in burned habitat. US Fish and Wildlife Service photo.

Two long-term case studies illustrate the general pattern of moose population response to postfire vegetation conditions in boreal forest (Kenai Peninsula) and mixed-transitional forest (Isle Royale). Other studies reported similar patterns, with moose population densities increasing as moose browse develops, peaking approximately 10 to 30 years after fire, and declining as moose browse abundance decreases. Scotter [250] observed 16 times more moose pellet groups/acre in 11- to 31-year-old postfire paper birch forests than in >120-year-old upland spruce forests in northern Canada:

Average number of moose pellet groups/acre in boreal forest stands since time of fire in the Northwest Territories, Saskatchewan, and Manitoba [250]
Time since fire (years) Number of pellet groups/acre
1-10 18
11-31 49
31-50 26
51-75 13
76-120 13
>120 3

Another study in the northern Canadian boreal forest reported that moose used burned areas within 1 year after fire, but use was highest 21 to 40 years after fire [276]:

Average number of moose pellet groups/acre in boreal forest stands since time of fire in the Northwest Territories, Saskatchewan, and Manitoba [276]
Time since fire (years) Number of pellet groups/acre
1-20 42
21-40 181
41-60 41
61-80 30
81-100 36
101-150 11
151-200 16
201-250 20
251-300 17

Moose population density increased 5- to 6-fold, 1 year after the 200-mile² (500 km²) Blair Lakes Fire in northeastern Alaskan boreal forest. Before the wildfire, moose density was extremely low (about 0.1 moose/km²). High moose use of the burn continued through the 4th year of the study [90]. Moose moved into burned areas 7 months after the Little Sioux Fire, a mid-May, 23-mile² (59 km²) mixed-severity wildfire with large areas of stand replacement in northeastern Minnesota mixed-transitional forest dominated by paper birch and balsam fir [204]. Moose continued to colonize the burn, and the second winter after the fire, moose density was 5 times prefire levels [205]. During April through November of postfire year 2, moose primarily used burned aspen-birch stands. Moose also frequently used balsam fir-birch stands, particularly from July through September. These stands produced the most forage biomass per unit area following the fire, suggesting that selection of these communities was related to forage abundance [116]. Rapid vegetation growth after the fire in conjunction with high moose densities in the area before the fire apparently accounted for the rapid colonization of the burn [205]. For more information on moose browse growth following fire, see Successional changes in browse.

Moose populations may not increase after fire until browse grows above the level of snow [154]. Moose temporarily left burned areas in the Little Sioux Fire, northern Minnesota, during mid- to late winter, when postfire sprouts were covered with snow. At this time, moose shifted from the burned areas to areas with conifer cover along the periphery of the burn [204].

Although moose populations generally increase in early succession as postfire shrub communities develop and decrease in late succession as shrub communities decline, not all fires produce habitat preferred by moose [159]. In 1953, Leopold and Darling (1953 cited in [159]) observed that "the mere passage of a fire through timberland (in Alaska) does not necessarily create optimum conditions for moose. Some burns produce a grassland stage; others come back in pure spruce; many produce aspen with little birch or willow which are the most palatable and productive browse plants". Koch [131] reported that because the browse species most prevalent in the moose diet were found in old lodgepole pine forests rather than in young forests, canopy removal in lodgepole pine forest was likely detrimental to moose occupying these forests. Moose populations are speculated to decrease following fire in areas where fires were historically infrequent (see Fire Regimes), and moose rely on late-successional habitats for food and cover. In central Idaho, moose used old-growth mixed-conifer/Pacific yew forests for food and cover during all seasons and used this habitat in greater proportions than its availability from September to June (P<0.01). Fire in this habitat was predicted to be detrimental to moose because moose's primary winter forage, Pacific yew, is easily killed by fire [213]. Rowe and Scotter [238] stated that in the uplands of the Precambrian (Canadian) Shield, suitable moose browse is seldom abundant following forest fires.

Postfire vegetation changes and succession: The effect of fire on moose habitats depends on many variables. The general successional courses in forests producing maximum benefits to moose populations are those involving paper birch-willow-aspen shrub thickets, but many successional courses are possible [103,154]. Postfire succession in black spruce forests in interior Alaska may be a simple cycle of black spruce self-replacement not beneficial to moose [119,154,159]. A fire in a poorly drained 3-mile² (8 km²) segment of the Chickaloon River, Alaska, for example, resulted in a pure, dense stand of black spruce that apparently never supported substantial moose browse [63].

Postfire vegetation succession is determined by several factors, including prefire vegetation composition, stand age, and postfire conditions such as presence of seeds and sprouting buds, seedbed quality, and weather. Ahlgren and Ahlgren [4] contended that very few generalizations can be derived from the literature concerning plant succession following fire in boreal forest. Nonetheless, many researchers have provided accounts of "typical" postfire vegetation sequences in boreal forest. In these accounts, the principal trees—black spruce, white spruce, jack pine, and quaking aspen—may be killed by fire but regenerate well on burned sites [271]. Fire consumes most of the understory plants, although many sprout after fire. In general, sprouting plants and plants with wind-disseminated seeds, such as aspen, birch, and willow, occur early in postfire succession [4]. A generalized postfire successional path to mature forest for spruce stands in boreal forest would likely pass through the following stages. The moss-herb stage occurs immediately following disturbance (0-5 years), with seedlings of woody species present if seeds are available and seedbed conditions (e.g., large openings with full sunlight and exposed mineral soil [154]) are favorable for establishment [167]. If seedlings and shrubs are not established—owing to a lack of sprouts, seeds, or suitable seedbed—the herb phase may dominate for an extended period [33]. Assuming either sprouts or seeds of trees and shrubs are available and seedbed conditions are favorable, the tall shrub-sapling stage succeeds the moss-herb stage (6-25 years) [167]. This stage is usually most important to moose because it provides the most abundant browse (see Moose population response to postfire vegetation changes). The dense tree stage dominated by either hardwoods or conifers follows, depending on the species present before the fire [154,165,167]. If hardwoods are present, then the stand progresses to the hardwood stage (25-100 years) [167] typically dominated by aspen and birch [33]. Tree mortality begins to open the stand, allowing some shrub and herb establishment in the understory. Conifer seedlings establish during the hardwood stage, with conifers becoming increasingly dominant. This results in a hardwood-conifer forest (60-80 years) [266]. In late succession (100-200 years) [167], these forests often succeed to spruce [266]. If no hardwoods are present, the tall shrub-sapling stage progresses directly to the spruce stage [33]. The spruce stage may support little moose browse [63].

Postfire vegetation succession in eastern mixed-transitional forests and Rocky Mountain conifer forests are also varied. Historically, many of these forests experienced occasional stand-replacing fire. In mixed-transitional forests of the northeastern United States and southeastern Canada, stand-replacement fires are typically followed by a flush of shrubs and saplings, including red and sugar maple, eastern white and red pine, quaking and bigtooth aspen, paper birch, alder, cherry, and serviceberry. Early in succession, oaks (Quercus spp.) often intermix with other hardwoods and pines. Balsam fir and red spruce invade the hardwood stands and gradually increase in dominance. On uplands, maples, yellow birch, American beech, and oaks typically dominate the usually long-lasting mature stage. On mesic sites, eastern hemlock dominates with red spruce, yellow birch, paper birch, and occasionally eastern white pine [271]. In the Rocky Mountains, stand-replacement fires in fir-spruce forests are typically followed by postfire establishment of conifer seedlings and sprouting hardwood shrubs, which dominate growth within a few years after fire. Regenerating stands often produce abundant moose browse until the tree canopy closes, typically >25 years after fire. In the northern Rocky Mountains, where lodgepole pine forests are mixed with fir-spruce forests, lodgepole pine regenerates rapidly after fire, often in dense stands [271].

Postfire vegetation succession depends on a number of factors including prefire site conditions and fire type [154]. Herbivory by moose and other browsers such as white-tailed deer and snowshoe hare may also impact the successional sequence and rate of vegetation change after fire (see Moose foraging effects) [33].

Prefire site conditions: Prefire vegetation composition and stand age play a substantial role in plant response to fire in moose habitats. Where sprouting woody plants were present before fire, revegetation of the site may be rapid, and the period of dominance by herbs may be very short "or perhaps nonexistent" [42]. Where sprouting woody plants are absent prior to the fire, or in areas where a fire is severe enough to completely kill sprouting plants and expose mineral soil, revegetation is mainly by seed, resulting in slow colonization of woody plants and prolonged dominance of herbs. Thus, immediately following a fire, there may be little browse to attract moose. If revegetation is by root sprouts, browse for moose may be present during the next growing season and occur in substantial amounts by the 3rd or 4th year after the fire. If revegetation is by seedlings, however, moose browse may not be present in appreciable amounts until postfire years 5 to 10.

Regardless of postfire regeneration method, browse is typically available to moose for about 25 years [42]. Following the Rosie Creek Fire in interior Alaska, a 14-mile² (35 km²) May stand-replacing wildfire, quaking aspen, paper birch, and willow sprouted from roots and root crowns and was abundant within 2 months. The fire occurred while plants were still dormant. It exposed mineral soil and left few islands of unburned vegetation within the burn perimeter. Moose foraged in the burn the 1st winter after the fire. Quaking aspen stands produced the most browse after the fire followed by white spruce, paper birch, and black spruce stands. Quaking aspen was the most abundant moose browse in the 1st postfire growing season, but moose use was highest on willows and paper birch and lowest on quaking aspen the 1st and 2nd spring following the fire. Seedling establishment of browse species was evident by the 3rd postfire growing season. Plant composition and age of the prefire community determined postfire vegetation growth. Quaking aspen, white spruce, and black spruce stands that were 70 years old produced 10 times more moose browse 3 years after burning than 130- to 180-year-old paper birch, white spruce, and black spruce stands combined. Black and white spruce stands that were 70 years old before the fire produced 3 times more moose browse 3 years after burning than did similar stands >140 years old before the fire [165]. Old stands of sprouting species may not be as productive after fire because of the ability of many of these species to sprout after fire decreases with age [33]. For example, 80% to 90% of 40- to 50-year-old paper birch trees produced stump sprouts within 1 year after cutting, while 40% to 50% percent of 100- to 125-year-old trees produced sprouts (see FEIS review of paper birch) [302].

The composition of species colonizing a burn may depend on site characteristics such as soil type. On the Kenai Peninsula, woody vegetation differed among soil types in 8- to 30-year-old postfire stands, with the density and frequency of willow and paper birch—principal moose forage—highest on loamy soils, and that of quaking aspen and mountain cranberry—secondary moose forage—most abundant on gravelly soils [194]. From these results, Peek [206] concluded that shrub populations that have similar fire regimes may respond differently to fire depending on soil type, and moose may alter their foraging and other habitat use accordingly.

Fire severity: In general, stand-replacing and severe understory fires (which kill or top-kill shrubs and young trees) are most likely to trigger high rates of moose emigration and lead to greater direct or indirect moose mortality than patchy or low-severity fires [163]. Tyers and Irby [286] reported that the winter after the mixed-severity Greater Yellowstone Area fires of 1988, most moose moved away from burned areas and concentrated in small patches of unburned and lightly burned conifer habitat within their home ranges or left their home ranges and moved to unburned conifer habitats. By the following spring, many moose had died from malnutrition. A subsequent study of the Greater Yellowstone Area fires reported that moose population density was reduced by about 75% from prefire levels and remained low until the end of the study in postfire year 14. Moose population densities were reduced most in areas where fire was severe. The fires converted about 30% of mature forests to early-seral stages [285]. The authors stated that the fires may have reduced moose survival during winter by reducing critical winter forage and cover [285,286]. In central Alaska, moose commonly used burns in their home range, but they selected unburned patches within the burns. Although only 15% of the area was unburned, 67% of moose locations in burned areas were in unburned patches. This suggested that the fire left enough forage in unburned areas to allow moose to remain in their home ranges [92].

Fire severity affects postfire conditions such as presence of seeds and sprouting buds and seedbed quality, which influence how soon after fire forage is produced for moose. These conditions interact with the timing of fire and weather to determine postfire vegetation dynamics and thus moose population response to fire [154,186]. Low-severity burned areas in moose habitats in Alaska, for example, were prone to colonization with unpalatable bluejoint reedgrass, whereas severe fires favored colonization by palatable fireweed (see Succession) [33,79]. In boreal forest of interior Alaska, quaking aspen forage was most abundant 1 to 5 years after fire, while paper birch and willow were most abundant 10 to 16 years after fire. Compared to areas where vegetation sprouted after fire, moose browse production was delayed 3 to 5 years in areas where moose browse species were killed by fire and forage species were seeded [301]. Moose browse was available during and immediately after a wildfire on the Tanana Flats, Alaska, in unburned islands within the burn perimeter and from sprouting browse in lightly burned areas [92]. Moose increasingly used the lightly burned areas for at least 4 years after the fire [92]. In contrast, moderately and severely burned stands (about 75% of the burned area) had little moose browse 1 to 5 years later [90]. After a late August mixed-severity wildfire that burned old-growth (200-300 years old) red and eastern white pine forest in southern Ontario, moose pellets were common at all burned sites. Some areas were burned severely with high rates of spread, with 100% tree mortality and total consumption of the organic soil layer. Other areas experienced low-severity surface fire, where red pine experienced low mortality but all balsam fir trees were killed. Many tree and shrub species important as moose browse (e.g., beaked hazelnut, birch, maple, and willow) sprouted by October. Seedling counts 1 year after the fire indicated that severely burned sites were succeeding to aspen, birch, and balsam fir, whereas low-severity sites were succeeding to red and eastern white pine [160].

According to a review by Johnstone and others [119], postfire hardwood tree growth and productivity are expected to be highest in black spruce forests with widespread mineral soil exposure (>30%) or very shallow (<1 inch (3 cm)) organic soils. In interior Alaska boreal forest, higher postfire browse density was reported in high-severity than low-severity burns. Fire severity was determined by the amount of residual soil organic matter following the fires. Two wildfires were examined. The Hajdukovich Creek Fire was a mixed-severity (61% severity, 6% medium, and 33% high severity) fire that burned 19 miles² (48 km²) of flat topography from mid-June to August, with ground smoldering until early October. The burn was 13 years old at the time of study. Prefire vegetation was black spruce with sparse quaking aspen and quaking aspen/black spruce stands. Postfire moose browse stem density declined significantly with increased soil organic matter depth (R²=0.42, P=0.002). Moderately and severely burned sites produced >3 times as much moose browse (mostly quaking aspen) as low-severity sites (P=0.02). Proportional moose removal of winter forage biomass was 3 times higher on high-severity sites compared with low- or moderate-severity sites (P<0.002). The other fire studied, the 14-mile² (35 km²) Rosie Creek Fire, was 22 years old at the time of study. Prefire vegetation consisted of 63- to 180-year-old stands of white spruce, black spruce, paper birch, and quaking aspen. Fire severity varied across the burn, ranging from 5% to 76% removal of the soil organic layer. Within the burn, area of hardwood stands had increased 400% by postfire year 22 [158]. For additional information on how fire affects the successional trajectory of plant species dominant in moose habitats, see FEIS reviews of species of interest.

Timing of burns: The composition of species colonizing a burn may depend upon timing of the fire relative to plant phenology. For example, willow species produce seeds that are viable for only a few weeks, and various species produce seeds at different times of year. Also, some species such as paper birch and white spruce produce large seed crops only once in several years, so the year of the fire may affect species composition of the resulting seral community [154]. For information on phenology and life history characteristics of plant species dominant in moose habitats, see FEIS reviews of species of interest.

Burn size and shape: The size and shape of the burn determines the amount of edge habitat created and the degree of interspersion of communities produced by fire, which in turn influence the fire's effect on moose populations. Discontinuous burning is most beneficial to moose and wildlife in general [42,161] because it provides cover close to feeding habitat, increased variety of forage species, and staggered maturation rates of individual stands [63,154]. The distance a moose moves from cover into open, burned areas to feed varies with season, weather, and individual age, gender, and reproductive status (see Predation risk). Generally, however, increased mature forest edge adjacent to burned areas appears to increase moose use of a burn. Moose may select edge habitats because mature stands provide protective cover and winter food [154].

In general, moose achieve highest year-round densities in heterogeneous landscapes with abundant edge habitat [154]. Landscape analysis of fall moose distribution relative to fire history in interior Alaska demonstrated this pattern. The densest moose populations occurred close to towns, at moderate elevations near rivers, and in areas where fire occurred between 11 and 30 years prior to the study [166]. Twenty-two years after the Rosie Creek Fire, landscape heterogeneity was greater than before the fire: patch size had decreased, edge area had increased, area of hardwood stands had increased, and area of conifer stands had decreased. In winter, moose tended to consume more forage in burned areas (28%) than unburned patches within the burn (18%). Models revealed that variation in moose forage consumption was best explained by landscape heterogeneity. The author suggested that variable fire behavior can create a spectrum of fire severities that may facilitate different successional pathways across the landscape, thus increasing landscape heterogeneity and the chances that a single fire will create favorable moose habitat [158].

Moose may avoid large burned areas or restrict movements to burn perimeters until vegetation is tall enough in the burn to provide cover. Moose selected edge habitat between burned and unburned forest on the Kenai Peninsula. Moose used an 11-year-old and a 33-year-old burned forest most often in the fall and winter. Moose using burned forest were located most frequently within 300 feet (100 m) of the unburned forest edge. Unburned forest and bogs were used most frequently in the spring and summer. When using unburned forest, moose were within 300 feet of the forest edge 89% of the time [22]. For more information on this study, see the Kenai Peninsula case study. The 1st and 2nd winters after the Little Sioux Fire in northern Minnesota, moose selected the periphery of the burn (0.25 mile (0.4 km) from the burn perimeter) more than unburned or interior parts of the burn (P<0.10) [116,187]. During May to September of the 2nd year, moose selected interior parts of the burn and moved back to the periphery of the burn after October. Moose remained in the periphery of the burn from October to the end of the study in December (P<0.10), suggesting a shift to dense cover in fall and winter. Even though unburned interior areas apparently had similar cover to that of the burn perimeter, moose were observed most often at the burn perimeter. This suggested that moose preferred cover near the burned area [116]. In a 40-acre (16 ha) quaking aspen-conifer stand in south-central Montana that was slashed and burned under prescription in spring, heaviest moose browsing occurred in burned areas adjacent to untreated forest where cover was dense. Moose browsing was lightest in the interior of the burn [97]. In north-central Canadian boreal forests, moose used the edges of large burns unless there were large, unburned inclusions within the burns. When using the large burns, moose often fled to unburned forests [276]. For more information on the importance of edge habitat to moose, see Cover.

Case studies:
Kenai Peninsula: Moose population density increased following 2 wildfires in lowland boreal forest on the Kenai Peninsula. Three to 6 years after a large (585 miles² (1,255 km²)) wildfire in 1947, moose population density increased 4-fold [254]. The wildfire was patchy, leaving about 60,000 separate unburned stands of mature forest within the burn perimeter and creating about 18,000 miles (11,000 km) of ecotone, thus creating abundant edge habitat [21,154,194]. The wildfire burned during mild summer weather from early June to mid-July [21,255]. No fire had occurred in the area for at least 50 years [255]. Initially, moose populations increased in the burn via immigration; then, they increased by increased reproduction [254,255]. Moose population density continued to increase >13%/year in the burn until postfire year 12. The population fluctuated around a peak population density between postfire years 13 and 24 and subsequently declined 10%/year to half of the peak population density by postfire year 29 [17]. A subsequent study found that moose population density continued to decline at approximately 9%/year until at least 43 years after the fire, when the study ended [157].

Moose population response to the 1947 fire was largely determined by postfire vegetation growth, which was influenced by vegetation type and fire severity [255]. Quaking aspen sprouted in many burned areas during the subsequent summer, providing some browse initially. Browse growth attracted moose to the burn within 5 years after the fire. In postfire year 5, unbrowsed quaking aspen was nearly 10 feet (3 m) tall. By this time, black spruce, paper birch, willow, and quaking aspen seedlings occurred throughout the burn [254]. Maximum browse biomass occurred postfire years 15 to 20. The moose population decline in later years appeared to result from severe winter weather between postfire years 25 to 29 and reduction in browse associated with plant succession and overbrowsing [28,157,193,193,254].

Moose population density also increased on the Kenai Peninsula following a 125-mile² (348 km²) wildfire in 1969 [194]. The fire occurred west of the 1947 burn, burned rapidly, and was very "hot", creating one large opening, leaving few unburned stands within its boundaries, and creating little edge habitat [21,194]. The fire burned for 3 weeks during August [21]. The burned areas began producing new moose forage rapidly following the fire. However, the large burn interior initially lacked hiding cover, which apparently limited moose use of the burn until postfire year 9 [194]. A subsequent study found that moose density in the burn increased until postfire year 13 and remained high until postfire year 21, when the study ended. Moose densities remained consistently low in nearby late-successional forests during postfire years 13 to 21 [157]. The increase in moose densities in the burned area during postfire years 13 to 21 was attributed to high moose production and low mortality, with some initial shifting of home ranges from adjacent high-density populations. Browse productivity peaked with peaks in moose population density, with maximum browse production approximately 15 years after the fire [247].

Isle Royale: Moose density increased in mixed-transitional forests on Isle Royale after a 1936 late July to mid-August wildfire that burned in 2 separate areas of the island. One burn was small (5 miles² (13 km²)); the other burn was large (41 miles² (106 km²)) [102]. The year of the fires, the moose population on the island was low following a winter die-off 2 years prior [102,121]. The moose population increased steadily on the island after the fire until postfire year 11, when moose population density was 4 times prefire levels [134]. Because of better interspersion of unburned patches of winter cover within the burn, the small burn apparently sustained high moose populations 2 years longer than the large burn [102]. The moose population on the island decreased significantly from postfire year 12 to postfire year 14 [102], apparently as a result of gray wolves establishing on the island at this time, but increased thereafter and remained stable at 5 times prefire levels until at least postfire year 33, when the study ended (P<0.01 for all variables) [102]. Moose browse roughly mirrored moose population dynamics. Initially, browse was reduced and remained low until postfire year 3. By postfire year 10, more browse was available in burned areas than in unburned areas [8]. The fire provided moose winter browse from postfire years 4 to 14; then the burned areas gradually became less important to moose as vegetation progressively grew out of reach [135]. By postfire year 33, moose used the burned areas very little ([135], Peterson 1977 cited in [206]).

Other factors: Several factors mediate moose use of burned areas, including local predation pressure, prefire travel patterns, and physical barriers.

Predation: Although moose habitat quality may increase after fire, low-density moose populations with high predation may not be able to respond to improved habitat conditions caused by fire [206,296]. For more information on this topic, see Survival.

Travel patterns: Burn use by moose is influenced by moose movements. Studies of moose in central Alaska after a May through June stand-replacing and mixed-severity wildfire indicated that increased use of burned areas by moose depended heavily on moose travel patterns before the fire [90]. The fire burned a 190-mile² (500 km²) area of mature black spruce forest, quaking aspen forest, and shrublands. Most (75%) of the area was moderately to severely burned; 10% was unburned. Moose living in or near the burn were not displaced by the fire. Moose forage was available during and immediately following the fire in unburned areas within the burn perimeter and soon after, from sprouting plants in lightly burned areas [92]. Moose with low prefire contact with the burned area increased use of the area following the fire by shifting home ranges to include more of the burned area and allocating more time to areas previously used only during migration (P<0.1 for all variables). Moose with high prefire contact with the area reduced their use of the area somewhat following the fire to include areas of abundant browse outside of the burn. Moose with no prefire contact did not use the burned area, despite close proximity (0.1-3.0 miles (0.2-4.8 km)), apparently because traditional movement patterns prevented them from finding the burn. In general, postfire use of the burn by moose was similar to prefire use until the summer following the burn. Moose increased use of the burn and established new movement patterns that incorporated the burn mostly during summer and during migration to rutting areas the first year following the fire (P<0.05), which ultimately amounted to a 5- to 6-fold increase in use of the burn by moose in postfire year 1. High use of the burn continued through the 4-year study [90]. This suggested that dispersal and migratory movements following the fire resulted in colonization of the burn.

Physical barriers: Postfire accumulation of deadfall might discourage use of burned habitats by moose by creating impassable areas. Moose did not use a 40-acre (16 ha) area in a 14-mile² (35 km²) burn where a convective firestorm had uprooted large diameter (19 inches (48 cm) DBH) white spruce, possibly hindering moose use of the burn [165]. In southeastern Ontario, Cumming [61] noted that moose avoided blowdown areas, apparently because deadfall densities were too high. Phillips [212] reported that postfire deadfall may render burns impassable to big game animals in general. Alternatively, Lyon and others [161] noted in a review that fire may benefit moose and other ungulates by removing movement obstructions such as deadfall.

Parasites: Severe winter tick infestations may be detrimental to moose (see Diseases and Sources of Mortality), and fire may reduce winter tick populations. A May prescribed fire in mature quaking aspen forest and willow habitat on Elk Island National Park, Alberta, reduced the number of engorged adult female ticks and larvae immediately after the burn. Winter ticks were killed by the fire. Winter tick survival depended upon the percent of duff consumed by the fire. Survival was highest where the burn was patchy and the percent of duff burned was lowest [68]. Although winter tick populations were reduced in the short term, fire's long-term effects on winter tick populations were unknown as of this writing (2010).

Irwin [116] speculated that fire may reduce populations of local terrestrial gastropod hosts of meningeal worm and thus reduce transmission of parelaphostrongylosis—a neurological disease—to moose. This is supported by evidence from north-central North America that suggested reduced forest cover, decreased ground surface moisture, and increased ground surface temperatures due to fire likely reduced habitat for and increase mortality of gastropods and meningeal worm larvae and curtailed transmissions [293]. However, Strayer and others [260] found no relationship between time since fire, clearcutting, or agriculture (2 to >69 years) and density, species richness, or composition of terrestrial gastropod communities in small (<25 acres (10 ha)) forested areas in northern New England. These results suggested that any fire effects on terrestrial gastropod populations were likely short term (<2 years), although large disturbances may have greater effects on gastropod populations than the small disturbances examined in this study [260].

FIRE REGIMES:
According to Thompson and Stewart [280], historically, wildfire was perhaps most influential in creating or maintaining moose habitat throughout the species' range in North America. Since the early 1900s, fire exclusion has reduced fire's influence on moose habitat throughout North America, except perhaps on the Kenai Peninsula and other northern locations where fire exclusion either was not practiced or was ineffective [280]. Bangs and Bailey [21], citing differences in the 1947 and 1969 wildfires on the Kenai Peninsula (see Kenai Peninsula case study), concluded that because fire suppression is generally most effective during mild summer weather and least effective during hot, dry weather, fire suppression was likely most effective in stopping the type of fire that created the highest quality moose habitat.

According to a review, historical fire-return intervals in boreal forests were relatively short, ranging from 50 to 100 years [271]. Some boreal forests were more susceptible to fire than others due to climate, topography, absence of water bodies, and types of vegetation [238]. Short intervals probably occurred in dry continental interior regions, whereas long rotations probably occurred in floodplains and in eastern boreal forests [271]. Historically, boreal forests had mostly stand-replacement fire regimes, although understory fires were common in some dry forest types [271]. Throughout large areas of the moose's geographic range, such as the Canadian Shield, wildfires were historically small because abundant interspersed wetlands prevented wildfire from sweeping vast areas. Frequent ignitions created a variety of forest stand age classes, resulting in a fine-grained mosaic of stands in various cover types and age classes [265]. Scotter (1970 cited in [238]) found that 8 years of fire reports for boreal forest in Saskatchewan showed >80% of fires were <100 acres (40 ha) and, in the transition between subarctic and closed boreal forests, 60% of fires were <10 acres (4 ha). In other parts of the moose's range such as Alaska and mountainous regions, fires were historically large, creating a large-grained mosaic of forest types and age classes [265]. Large fires historically occurred in Yukon where spruce-pine stands have a low component of quaking aspen and birch, and fires are able to spread more easily than in mixed-transitional forests that have "built-in broadleaf fire-breaks" [238]. Mean fire size in boreal forest in Labrador was historically 49 miles² (127 km²) and in Quebec was 30 miles² (78 km²) [115].

In the mixed-transitional forest region, historical fire frequency varied from 50 to 1,000 years. Fire rotations ranged from 50 to 100 years in jack pine, black spruce, and spruce-fir forests, from 150 to 300 years in red and eastern white pine forests, and sometimes exceeded 1,000 years in northern hardwood forests [271]. In mixed-transitional forests, the proportion of early-successional stands was small at any given time, but when fires occurred, they were often large [271]. Historically, mixed-transitional forests were characterized by stand-replacement and mixed-severity fires, although understory fires occurred as well. Stand-replacing fires predominated in jack pine, black spruce, and spruce-fir forests, and mixed-severity fires predominated in red and eastern white pine forests [271].

Historical fire-return intervals in Rocky Mountain forests ranged from <10 years to >300 years [271]. Rocky Mountain forests experienced understory, mixed-severity, and stand-replacement fires. Stand-replacing and mixed-severity fires were common in subalpine fir-Engelmann spruce and lodgepole pine forests, but understory fires also occurred, especially on dry sites. Forests with a multistoried structure, including dense thickets of young conifers, were more likely to experience stand-replacing fire than open, park-like stands. When ignition occurred in lodgepole pine forests, old stands were more likely to burn than young stands [271].

Moose commonly occur in habitats where fire was historically infrequent. Fire was historically infrequent in tundra and subalpine shrublands because large quantities of fuels do not accumulate and consequently, fires do not carry well except during the driest conditions [288]. Moose also occur in mesic maritime forests of eastern Canada and New England and in western British Columbia and parts of southeastern Alaska where fires were historically infrequent [206]. According to Buckley [42], interior Alaska is subject to frequent, severe fire due to low precipitation, but wildfires are rare in southeastern Alaska, where precipitation is high and forests are "virtually fireproof".

Many sources providing information on fire regimes of moost habitats are available. For northern regions, including those with mixed fire regimes (e.g., quaking aspen, eastern white pine, red pine, and jack pine forests) and stand-replacement fire regimes (e.g., black spruce, white spruce, red spruce, and balsam fir forests; conifer bogs; and tundra), see Duchesne and Hawkes [69]. For information on fire regimes in northern hardwoods, see Wade and others [292]. See Arno [11] for information on fire regimes in western forest ecosystems including those with understory fire regimes (e.g., ponderosa pine, Jeffrey pine (Pinus jeffreyi), and ponderosa pine-mixed conifer forests), mixed fire regimes (e.g., Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca), Rocky Mountain lodgepole pine (P. contorta var. latifolia), and ponderosa pine forests), and stand-replacement fire regimes (e.g., fir-Douglas-fir-western larch, Rocky Mountain lodgepole pine, western white pine (P. monticola)-western redcedar-western hemlock, subalpine fir-Engelmann spruce-whitebark pine, and quaking aspen). The Fire Regime Table summarizes characteristics of fire regimes for vegetation communities in which moose may occur. Follow the links in the table to documents that provide more detailed information on these fire regimes.

FIRE MANAGEMENT CONSIDERATIONS:
According to Thompson and Stewart [280], the "most convincing evidence that habitat management could have a positive influence on moose populations is the fact that historically moose populations have increased when habitat has been created or rejuvenated" by disturbance. For example, moose populations increased dramatically on the Kenai Peninsula as a result of new habitat created by wildfires in 1947 and 1969 (see Kenai Peninsula case study). A similar increase in moose abundance occurred on Isle Royale after a 1936 fire (see Isle Royale case study). Several researchers have reported increases in moose browse quantity and nutritive quality after prescribed burning [12,13]. See Successional changes in browse for more information on this topic. Thus, researchers suggested that prescribed fire may be used on a site-specific basis to improve moose browse [280]. Prescribed fire can be manipulated to intersperse early- and late-successional forests and increase edge. MacCracken and Viereck [165] suggested using patchy prescribed fire in a variety of plant communities to create a mosaic of stand age classes to provide immediate and long-term browse as well as diverse forage species for moose.

Heinselman [105] recommended that management practices mimic historical disturbance regimes. Historically, large, stand-replacing fire often occurred in boreal forests (see Fire Regimes). However, prescribed fires of this scope are difficult to accomplish [280]. Because use of prescribed fire may be limited, managers in Alaska advocate that wildfires be allowed to burn if they pose no threat to human life or property [29,105]. In 1988, Bishop [29] suggested that the result of such a policy would be "the occurrence and influence of wildfire on large areas" becoming "more like the natural fire regime which preceded extensive fire suppression". Some researchers recommended that prescribed fires and wildfires for resource benefit be combined with other habitat management techniques, such as clearcutting, and with population management techniques, such as hunting restrictions, to increase moose densities [230].

Postlogging site preparation practices employed in moose habitats often include burning of harvest residues and slash piles or understory burning [50]. Some researchers reported improved browse availability after clearcutting and burning compared to clearcutting alone. Crawford and others [57] found that available digestible energy of browse in balsam fir-spruce forest in eastern Maine was greatest in clearcut plots and plots burned under prescription (P<0.05) [57]. Another researcher reported similar effects of cutting and prescribed fire. In eastern Maine, moose browse availability in 60- to 80-year-old spruce-balsam fir stands was highest on a plot burned in a wildfire 14 years prior to the study, intermediate on recently disturbed plots (≤5 years old), and lowest on undisturbed plots. Moose browse availability was similar among recently disturbed plots, which included plots clearcut after spruce budworm defoliation, plots clearcut and burned under prescription after spruce budworm defoliation, and a plot burned in a wildfire 5 years prior to the study. Recently disturbed plots had >9 times more available browse during the growing season than undisturbed plots, and the 14-year-old burned plot had >13 times more browse during the growing season than undisturbed plots [147]. Another researcher described better browse production on clearcut plots than plots burned under prescription. Three years after cutting and burning 20-year-old quaking aspen stands in the Great Lakes-St Lawrence forest region, summer and winter quaking aspen browse production was greatest on cutting treatments conducted prior to vernal leaf flushing ("preflush"), followed by postflush cutting, postflush prescribed surface burning, and preflush prescribed burning. The author concluded that cutting prior to spring green-up was optimal for creating year-round moose browse. Conversely, burning prior to leaf-out reduced quaking aspen to a minor component of the stand 3 years later because the fire killed most mature quaking aspen. The author reported that burning too frequently in quaking aspen stands eliminates quaking aspen [294]. In general, severe and repeated burning reduces shrub reproduction and consequently reduces browsing wildlife [161]. See the FEIS review of quaking aspen and other species of interest for fire management recommendations.

Site selection: Because postfire vegetation composition is partly related to prefire vegetation composition and age (see Postfire vegetation changes and succession), Boucher [33] recommended selecting sites for prescribed burning where reproductive moose browse species are already present. Fire severity and timing of fire can then be manipulated to influence postfire vegetation development. In her review of vegetation response to fire in boreal forest in Alaska, she recommended targeting early- to midseral forests where browse species such as paper birch and Scouler willow are abundant before fire to maximize postfire browse production. She recommended that burning take place across a wide range of conditions. A spring fire on frozen ground was recommended to maximize postfire production of sprouting species. During years when fuels are dry enough to carry a fire, a late summer or fall fire was recommended to expose mineral soil and provide a favorable seedbed for seedling establishment of woody species. In the latter case, she recommended the fire be severe enough to expose mineral soil but not so severe that it kills underground propagules of desired browse species. If fuels are not adequate to carry a fire that exposes mineral soil, she recommended cutting trees prior to prescribed burning to increase the fuel load sufficiently to create the desired burn severity [33]. However, fire in late summer or fall is often considered detrimental to moose because it reduces winter forage availability (see Season).

Because not all fires create moose habitat, researchers recommended selecting sites for burning under prescription that target locally preferred browse species. In north-central Idaho, where moose occupied old-growth grand fir/Pacific yew forest, use of prescribed fire was not recommended because Pacific yew, an important browse species, is susceptible to fire-caused mortality [208]. Where prescribed fire is applied to selection cuts in this habitat, piling and burning was considered better than broadcast burning for maintaining some Pacific yew in the subcanopy [213]. In general, patchy prescribed fires that maintain some available browse are recommended in moose habitats [165]. Because moose use burned areas adjacent to conifer cover, Gordon [97] recommended that prescribed fire be used in areas with nearby conifer forest.

Season: Many researchers recommended spring and summer prescribed fire in moose habitats. This allows for some forage growth in the same growing season, thus providing forage for moose soon after fire and into the subsequent winter. Late summer or fall burning in moose habitats may delay forage growth until the following spring and reduce winter forage availability [92,165]. Bangs and Bailey [21] surmised that calf recruitment could be low in springs following fires that reduce vegetation on wintering grounds.

Spring prescribed fire may be an effective management tool to reduce winter tick populations. To control engorged females that would otherwise lay eggs, the period between snowmelt and leaf-out, when adult winter ticks fall off moose and occur in duff, may be the best time of year for prescribed fire that uniformly consumes high amounts of duff. Late summer to fall prescribed fire (early September-early October), when winter tick larvae infest moose, may decrease winter tick larvae populations but was not recommended because fall fire also reduces the amount of forage available to moose during the subsequent winter [68].

Frequency: Frequent fire may eliminate some important moose browse species [255]. For example, quaking aspen may fail to sprout with fires at 2- to 3-year intervals [39].

Burn size and shape: The size and shape of the burn affect moose habitat quality. Large, heterogeneous prescribed burns producing abundant edge habitat and with unburned remnant forest inclusions appear most beneficial to moose populations. Several researchers noted that small burns were more prone to overbrowsing by moose than large burns [199]. Komarek [132] noted that "on the Kenai National Moose Range in Alaska, I found that the moose are so attracted to burned over land that controlled burning experiments were most difficult to maintain because of the over-grazing by these animals. Apparently the burns are going to have to be of considerable size to be effective".

APPENDIX: FIRE REGIME TABLE

SPECIES: Alces americanus
The following table provides fire regime information that may be relevant to moose habitats. Follow the links in the table to documents that provide more detailed information on these fire regimes.

Fire regime information on vegetation communities in which moose may occur. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models [140], which were developed by local experts using available literature, local data, and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Pacific Northwest Southwest Northern and Central Rockies Northern Great Plains Great Lakes
Northeast        
Pacific Northwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northwest Forested
Dry ponderosa pine (mesic) Replacement 5% 125    
Mixed 13% 50    
Surface or low 82% 8    
Douglas-fir-western hemlock (dry mesic) Replacement 25% 300 250 500
Mixed 75% 100 50 150
Douglas-fir-western hemlock (wet mesic) Replacement 71% 400    
Mixed 29% >1,000    
Lodgepole pine (pumice soils) Replacement 78% 125 65 200
Mixed 22% 450 45 85
Spruce-fir Replacement 84% 135 80 270
Mixed 16% 700 285 >1,000
Southwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Southwest Forested
Riparian forest with conifers Replacement 100% 435 300 550
Riparian deciduous woodland Replacement 50% 110 15 200
Mixed 20% 275 25  
Surface or low 30% 180 10  
Aspen with spruce-fir Replacement 38% 75 40 90
Mixed 38% 75 40  
Surface or low 23% 125 30 250
Stable aspen without conifers Replacement 81% 150 50 300
Surface or low 19% 650 600 >1,000
Lodgepole pine (Central Rocky Mountains, infrequent fire) Replacement 82% 300 250 500
Surface or low 18% >1,000 >1,000 >1,000
Spruce-fir Replacement 96% 210 150  
Mixed 4% >1,000 35 >1,000
Northern and Central Rockies
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northern and Central Rockies Shrubland
Riparian (Wyoming)
Mixed 100% 100 25 500
Northern and Central Rockies Forested
Ponderosa pine (Northern and Central Rockies) Replacement 4% 300 100 >1,000
Mixed 19% 60 50 200
Surface or low 77% 15 3 30
Ponderosa pine-Douglas-fir Replacement 10% 250   >1,000
Mixed 51% 50 50 130
Surface or low 39% 65 15  
Western redcedar Replacement 87% 385 75 >1,000
Mixed 13% >1,000 25  
Douglas-fir (xeric interior) Replacement 12% 165 100 300
Mixed 19% 100 30 100
Surface or low 69% 28 15 40
Douglas-fir (warm mesic interior) Replacement 28% 170 80 400
Mixed 72% 65 50 250
Douglas-fir (cold) Replacement 31% 145 75 250
Mixed 69% 65 35 150
Grand fir-Douglas-fir-western larch mix Replacement 29% 150 100 200
Mixed 71% 60 3 75
Mixed conifer-upland western redcedar-western hemlock Replacement 67% 225 150 300
Mixed 33% 450 35 500
Western larch-lodgepole pine-Douglas-fir Replacement 33% 200 50 250
Mixed 67% 100 20 140
Grand fir-lodgepole pine-larch-Douglas-fir Replacement 31% 220 50 250
Mixed 69% 100 35 150
Persistent lodgepole pine Replacement 89% 450 300 600
Mixed 11% >1,000    
Whitebark pine-lodgepole pine (upper subalpine, Northern and Central Rockies) Replacement 38% 360    
Mixed 62% 225    
Lower subalpine lodgepole pine Replacement 73% 170 50 200
Mixed 27% 450 40 500
Lower subalpine (Wyoming and Central Rockies) Replacement 100% 175 30 300
Upper subalpine spruce-fir (Central Rockies) Replacement 100% 300 100 600
Northern Great Plains
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northern Plains Woodland
Great Plains floodplain Replacement 100% 500    
Great Lakes
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Great Lakes Forested
Northern hardwood maple-beech-eastern hemlock Replacement 60% >1,000    
Mixed 40% >1,000    
Conifer lowland (embedded in fire-prone system) Replacement 45% 120 90 220
Mixed 55% 100    
Conifer lowland (embedded in fire-resistant ecosystem) Replacement 36% 540 220 >1,000
Mixed 64% 300    
Great Lakes floodplain forest
Mixed 7% 833    
Surface or low 93% 61    
Great Lakes spruce-fir Replacement 100% 85 50 200
Minnesota spruce-fir (adjacent to Lake Superior and Drift and Lake Plain) Replacement 21% 300    
Surface or low 79% 80    
Great Lakes pine forest, jack pine Replacement 67% 50    
Mixed 23% 143    
Surface or low 10% 333
Maple-basswood Replacement 33% >1,000    
Surface or low 67% 500    
Maple-basswood mesic hardwood forest (Great Lakes) Replacement 100% >1,000 >1,000 >1,000
Maple-basswood-oak-aspen Replacement 4% 769    
Mixed 7% 476    
Surface or low 89% 35    
Northern hardwood-eastern hemlock forest (Great Lakes) Replacement 99% >1,000    
Red pine-eastern white pine (frequent fire) Replacement 38% 56    
Mixed 36% 60    
Surface or low 26% 84    
Red pine-eastern white pine (less frequent fire) Replacement 30% 166    
Mixed 47% 105    
Surface or low 23% 220    
Great Lakes pine forest, eastern white pine-eastern hemlock (frequent fire) Replacement 52% 260    
Mixed 12% >1,000    
Surface or low 35% 385    
Eastern white pine-eastern hemlock Replacement 54% 370    
Mixed 12% >1,000    
Surface or low 34% 588    
Northeast
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northeast Forested
Northern hardwoods (Northeast) Replacement 39% >1,000    
Mixed 61% 650    
Eastern white pine-northern hardwoods Replacement 72% 475    
Surface or low 28% >1,000    
Northern hardwoods-eastern hemlock Replacement 50% >1,000    
Surface or low 50% >1,000    
Northern hardwoods-spruce Replacement 100% >1,000 400 >1,000
Beech-maple Replacement 100% >1,000    
Northeast spruce-fir forest Replacement 100% 265 150 300
*Fire Severities
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [101,139].

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SPECIES: Alces americanus
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