SPECIES: Larix occidentalis

INTRODUCTORY

SPECIES: Larix occidentalis

 

Photo courtesy of RMRS Photo by Rick Wallace

AUTHORSHIP AND CITATION:
Scher, Janette S. 2002. Larix occidentalis. 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:
LAROCC

SYNONYMS:
none

NRCS PLANT CODE [154]:
LAOC

COMMON NAMES:
western larch
hackmatack
western tamarack

TAXONOMY:
The currently accepted scientific name for western larch is Larix occidentalis Nutt. (Pinaceae) [50,76,154].

Natural hybridization of western larch and alpine larch (Larix lyallii) has been documented in the Carlton Ridge Research Natural Area and in the Cabinet Mountains and Bitterroot Range of Montana, where the species are sympatric. Usually, however, western larch and alpine larch are isolated by elevation [26,27,31]. Carlson and Ballinger [28] reported that 1st generation western larch-alpine larch crosses are viable. Carlson and others' [27] literature review reported successful crosses of western larch with European larch (L. decidua) and with Japanese larch (L. kaempteri).

LIFE FORM:
Tree

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
No entry


DISTRIBUTION AND OCCURRENCE

SPECIES: Larix occidentalis
GENERAL DISTRIBUTION:
Western larch occurs from southeastern British Columbia and extreme western Alberta southward into eastern Washington, western Montana, northern Oregon, and northern and west-central Idaho [40,46,72,115]. It has been established in a planting in Salt Lake County, Utah [157], and one source reports that its range extends into Colorado [70].

ECOSYSTEMS [53]:
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES22 Western white pine
FRES23 Fir-spruce
FRES24 Hemlock-Sitka spruce
FRES25 Larch
FRES26 Lodgepole pine

STATES:
ID MT OR UT WA WY
AB BC

BLM PHYSIOGRAPHIC REGIONS [22]:
2 Cascade Mountains
5 Columbia Plateau
8 Northern Rocky Mountains
9 Middle Rocky Mountains
16 Upper Missouri Basin and Broken Lands

KUCHLER [81] PLANT ASSOCIATIONS:
K004 Fir-hemlock forest
K010 Ponderosa shrub forest
K011 Western ponderosa forest
K012 Douglas-fir forest
K013 Cedar-hemlock-pine forest
K014 Grand fir-Douglas-fir forest
K015 Western spruce-fir forest

SAF COVER TYPES [42]:
205 Mountain hemlock
206 Engelmann spruce-subalpine fir
210 Interior Douglas-fir
212 Western larch
213 Grand fir
215 Western white pine
218 Lodgepole pine
220 Rocky Mountain juniper
224 Western hemlock
226 Coastal true fir-hemlock
227 Western redcedar-western hemlock
228 Western redcedar
233 Oregon white oak
237 Interior ponderosa pine

SRM (RANGELAND) COVER TYPES [134]:
409 Tall forb

HABITAT TYPES AND PLANT COMMUNITIES:
Except when it is young, western larch is rarely found in pure stands. Its most common tree associate is Douglas-fir (Pseudotsuga menziesii), and on low-elevation dry sites it is found with ponderosa pine (Pinus ponderosa). Common associates in warm, moist forests include grand fir (Abies grandis), western hemlock (Tsuga heterophylla), western redcedar (Thuja plicata), and western white pine (P. monticola). In cool, moist, subalpine forest types Engelmann spruce (Picea engelmannii), subalpine fir (A. lasiocarpa), lodgepole pine (Pinus contorta), and mountain hemlock (Tsuga mertensiana) are more common.

Hardwoods that occur with western larch include paper birch (Betula papyrifera), black cottonwood (Populus balsamifera ssp. trichocarpa), and quaking aspen (P. tremuloides) [72,115,116,126,132].

Major understory associates include common beargrass (Xerophyllum tenax), huckleberry (Vaccinium spp.), thimbleberry (Rubus parviflorus), menziesia (Menziesia ferruginea), ninebark (Physocarpus malvaceus), serviceberry (Amelanchier spp.), Oregon boxwood (Paxistima myrsinites), and bearberry (Arctostaphylos uva-ursi).

Western larch is not considered a climax species, but it is a long-lived early successional species. Refer to Successional Status for more details [34,53,88,116,156]. Classifications describing plant communities in which western larch is an important seral species include the following:

Idaho: [33,34,64,144]
Montana: [65,66,106]
Oregon: [51,63]
Washington: [34,51,63]


BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Larix occidentalis
GENERAL BOTANICAL CHARACTERISTICS:
Western larch is a fast growing, long-lived, deciduous conifer native to alpine and subalpine forests of the northwestern United States and adjacent Canada [4,45,115,154]. Trees over 900 years old have been reported [80,115,116].

One of the world's largest larches, western larch typically grows 100 to 180 feet tall (30-55 m) but can be over 200 feet (60 m) tall [50,57,71,72,115,157], with diameters up to 6 feet (2 m) [50,62,72,157]. Basal area increases rapidly to about age 40, then decelerates and nearly levels off after age 100 [115]. A deep, spreading root system stabilizes these large trees [57,72]. In a synthesis of literature on northwestern trees, Minore [93] ranked western larch root depth in the middle category of 5 categories.

Bark in mature trees is thick and furrowed into large, flaky plates [50,71,115,157]. At age 50, basal bark thickness ranges from 5 to 10 inches (12-25 cm), and at age 100 bark is 10 to 18 inches (25-45 cm) thick [12]. Western larch trunks are usually bare for a half to a third of the height when in stands, while trees in the open may have branches to within a few feet of the ground [71,72,157]. Crowns are generally short, open, and pyramidal with nearly horizontal branches, though branches may droop in the lower crown of older trees grown in the open [50,57,71,72]. Crown length, width, and density were all ranked low in Minore's [93] synthesis of literature on northwestern trees.

Branches are stout and brittle, changing from pubescent to glabrous with age. Buds are small, rounded, and hairless [71,72,157]. As trees mature, clustered epicormic branches replace older branches, beginning with the lower portion of the crown. Eventually, epicormics, which grow from dormant buds at the base of first order branches, comprise the entire crown [83].

Clusters of 15 to 30 slender, soft, spirally-arranged needles 1 to 2 inches (2.5-5.0 cm) long arise from dwarf twigs [71,72,157]. Western larch foliage is replaced annually [55,57].

Male western larch cones are 0.4 inch (1 cm) long [71,157]. Ovulate cones are papery, 1 to 1.5 inches long (2.5-3.5 cm) and 0.5 to 0.6 inch (1.3-1.6 cm) wide with long subtending bracts [12,50,71,72,157]. Seeds are 0.1 inch (3 mm) long with 0.2 inch (6 mm) wings [50,71,72,157].

The preceding description provides characteristics of western larch relevant to fire ecology and is not meant to be used for identification. Keys for identifying western larch are available [40,70,82].

RAUNKIAER [107] LIFE FORM:
Phanerophyte

REGENERATION PROCESSES:
Breeding system: Western larch is monoecious with both staminate and ovulate cones distributed throughout the crown [115,116].

Pollination: Western larch pollen is distributed by wind and is less abundant than that of other conifers. Owens [101] described the physiological details of pollination in western larch.

Seed production: Western larch cone production may begin as early as age 8 though it is unusual on trees less than 25 years old. Heavier crops usually begin at approximately 40 to 50 years of age and continue for 300 to 500 years [116,130]. Trees usually produce cones annually, but crop size varies with year and location; heavy cone crops occur every 5 years on average, with fair to poor crops in other years [115,121]. Shearer and Carlson [121] reported an annual average of 1,393 potential cones per tree over a 6-year period. Because western larch cones are borne throughout the crown, the size of the crop generally corresponds to the size of the crown [115,116,117]. Shearer and Kempf's [132] literature review indicated that the number of cones also increases with increased spacing of trees.

Western larch seeds are small and light, just 137,000 to 143,000 per pound (301,00-315,00/kg) [12,115,154]. On average each mature cone produces 39 seeds, but some may contain as many as 80, and mature stands of western larch may produce more than 0.5 million seeds per acre (1.2 million seeds/hectare) [115]. Roe [111] described a method for estimating the size of western larch seed crops up to 1 year in advance.

Viability of seeds typically increases with crop size and decreases with tree age [115]. Inviable seed results from lack of pollination, inviable pollen, lack of fertilization, later ovule abortion, or embryo abortion [102]. Over a 6-year period, Shearer and Carlson [121] found that 4% of potential seeds at the time of bud burst matured as filled seeds.

Seed dispersal: Most of western larch's small, light, long-winged seeds are distributed within 328 feet (100 m) of the parent. However, depending on wind conditions, they may be dispersed up to 820 feet (250 m) or more [116]. This distance is comparable to that of Engelmann spruce seeds, but is longer than Douglas-fir and subalpine fir [115]. Seed spread rate is considered moderate [154].

Seed banking: Western larch seeds are viable only until the year following fertilization [117].

Germination: Seeds of western larch germinate well on a variety of seedbeds and aspects [117], but Stoehr [147] found that germination and survival was greatest in mineral soil. In a synthesis of literature on northwestern trees, Minore [93] ranked western larch germination and survival in the highest category for mineral seedbeds, in the middle category for burned seedbeds, and in the lowest category for organic seedbeds. The ideal temperature for germination is 80 Fahrenheit (27 C), but germination can occur at temperatures as low as 65 Fahrenheit (18 C). Germination occurs at or above the soil surface. Natural stratification during winter results in rapid, complete germination. Spring-sown western larch seeds without stratification germinate slowly and erratically; some do not germinate until the following season [115]. Oswald [100] reported seed predation and shade both had negative effects on germination rates of western larch, though shading was not a significant factor. Shade appears to be more important as seedlings develop.

Seedling establishment/growth: On average 1 western larch seedling will establish for every 53 seeds produced and dispersed [127]. Seedlings grow rapidly and vigorously [115,154], averaging 2 inches (5 cm) of growth during the 1st season and 12 inches (30 cm) per year over the next 4 years. Western larch seedlings grow faster than all major associates except lodgepole pine, and the species grows faster than any other Rocky Mountain conifer until 100 years of age [12,115].

Site variation: Site requirements for establishment and growth of western larch seedlings are more specific than those for germination. Seedlings are well adapted to the mineral soil and sunlight of exposed seedbeds, such as those created by burning or mechanical scarification. They do not thrive in areas with undisturbed litter, humus, sod, or heavy root competition [12,54,115,116,117,123]. Overly dense stands slow growth. For the 1st few years shaded seedlings usually grow faster than those in full sunlight; thereafter, seedlings in full sunlight outgrow shaded seedlings. North, northwest, and northeast exposures and gentle to flat topography are best for seedling survival; high surface temperatures on south and west exposures may kill many seedlings [115].

Mortality: Seedling mortality is usually highest in the 1st season; losses after year 3 are minimal [115]. Biotic factors, such as fungi, birds, and rodents, cause the most 1st year seedling deaths early in the season, but drought is more detrimental after mid-July [115,117]. Newly germinated seedlings were killed by high soil-surface temperatures (>130 Fahrenheit (54 C)) in Montana, and these effects were most severe on western and southern exposures [117,122].

Asexual regeneration: Western larch does not reproduce by sprouts, but propagation by cuttings has been successful [115].

SITE CHARACTERISTICS:
Western larch occurs in mountain valleys and lower slopes, often in somewhat swampy areas [50,71]. It needs well-lighted areas for maximum development, so it performs best in open stands [72]. Western larch is usually found at elevations of 1,500 to 5,500 feet (460-1,700 m) in the northern portions of its range and may be found at elevations over 7,000 feet (2,100 m) in the southern parts of its distribution [50,72,117]. Latitude and elevation affected genetic variation patterns of western larch populations in the Rocky Mountains. Populations from more northern areas and from high elevations had lower growth potential, lower resistance to disease, and lower survival [108]. Elevational ranges for some states and 1 province in western larch's range are:

Montana 3,000-7,200 feet (900-2200 m) [12,79]
Oregon 3,500-6,500 feet (1000-2000 m)
Washington 2,000-5,500 feet (600-1700 m) [79]
British Columbia 2,000-5,550 feet (600-1700 m) [12]

Climate: Western larch occupies relatively cool, moist climatic zones. Its upper elevational range is limited by low temperatures, while the lower extreme is limited by low precipitation [45,46,115,117].

Average climatic conditions for western larch's range are [115]:

Temperature 45 Fahrenheit (7 C)
Maximum temperature 84 Fahrenheit (29 C)
Minimum temperature 15 Fahrenheit (-9 C)
Growing season temperature 60 Fahrenheit (16 C)
Frost free days 60-160 days
Annual precipitation 28 inches (710 mm)
Growing season precipitation 6 inches (160 mm)
Snowfall 103 inches (2620 mm)

Climatic conditions for 4 forest habitat types where western larch occurs are [45]:

Douglas-fir grand fir western redcedar-
western hemlock
Engelmann spruce-
subalpine fir
Mean annual precipitation (mm) 370-570 500-680 570-1,130 700-850
Mean growing season precipitation (mm) 180-270 200-290 210-370 200-320
Mean annual snowfall (cm) 120-350 193-450 130-560 200-620
Mean annual temperature (C) 4.0-7.5 2.5-4.0 2.5-7.8 1.0-2.5
Frost-free conditions (days/year) 40-140 35-80 50-170 40-70

Soil: Western larch is found on a wide variety of soil types, most of which are derived from bedrock or glacial till, but some are of  loessial or volcanic ash origin. Deep, porous soils, such as those of mountain slopes and valleys are ideal, and growth is related to soil depth [46,72,115,116,117]. Western larch is also quite dependent on mineral soil or burned seedbeds, more so than any associated tree species including lodgepole pine [46,115]. Western larch is adapted to medium and coarse textured soils with a pH of 6 to 7, and has no salinity tolerance [154].

Topography: Western larch occupies valley bottoms, benches, and mountain slopes. It is found on all exposures but is more common on north and east aspects. South and west exposures are often too severe for seedling establishment [115,116]. This trend is more pronounced in the southern parts of its range, where it is found almost exclusively on north- and east-facing slopes [45,46].

Harsh environments: Western larch has moderate to high resistance to wind throw because its root system provides good anchorage. It is adapted to a wide range of temperatures, but since buds open earlier than associated conifers, hard frosts in late spring may result in cone crop loss [117]. Frozen seed cones are associated with nighttime air temperatures of 25 Fahrenheit (-4 C) or less [27,130]. Snow and ice are generally not threats to western larch survival. Wet snow when needles are present (early spring or late fall) may cause snow bend, but rarely results in permanent damage [117].

SUCCESSIONAL STATUS:
Western larch is the least shade tolerant conifer in its range [11,45,46,48,116]. As such, it is a seral species whose populations have been historically maintained by disturbances such as wildfire and glacial retreats [45,46,116,126] and is therefore usually found in even-aged stands [116]. It is an aggressive pioneer species after fire or other major disturbance [11,46,61,88] and competes best on moist sites [48,61]. In drier environments where fires are frequent, western larch may form a "fire climax" [152].

Western larch uses nitrogen more efficiently than evergreen trees, reducing its dependence on soil for nitrogen and increasing its effectiveness as a pioneer in disturbed, infertile habitats [56,149]. This aggressive pioneer quickly colonizes disturbed areas and grows rapidly, remaining taller than its associates for approximately 100 years [45,46,116,126]. Western larch's rapid height growth may indicate allocation of resources to early growth rather than early seed production, which would explain the species' relatively advanced age of 1st reproduction compared to other early successional species. Western larch extension growth was significantly greater than that of 6 other northwestern conifers. This characteristic and low shade tolerance were both associated with early successional species studied [152].

In the absence of disturbance, shade tolerant associates form understories that shade out future generations of western larch seedlings [116]. However, western larch's long lifespan and resistance to damage from fire and pathogens accounts for the presence of relict trees in late-successional stands that can repopulate the stand if fire or other disturbance removes competition and opens the canopy [45].

SEASONAL DEVELOPMENT:
Western larch's active growth occurs from May through August [115,154]. Vegetative development of western larch proceeds as follows:

Stage of Development Timing
Buds begin to appear early fall [115]
Buds swell, then open late March and April [121]
Needle growth declines mid-May
Diameter growth begins mid-May
Diameter growth peaks, needle growth ends, height growth begins mid- to late June
Height growth peaks mid-July
Height growth complete mid-August [132]

Reproductive development in western larch proceeds as follows:

Stage of Development Timing Notes
Cone initiation early summer [101,115] ----
Buds appear early fall [115] ----
Pollen and seed cone buds develop prior to winter dormancy [101,115] ----
Pollen and seed cone development begins late March and April [121] ----
Pollen and seed conelets appear mid-April to mid-May ----
Pollination late April to early June [115] ----
Fertilization June to July [102,115] Fertilization occurs 6-8 weeks after pollination.
Cones mature mid- to late August Cones mature faster during warmer summers.
Cone opening begins late August and early September [115,117] Long periods of cool or moist weather may delay opening [115].
80% of seeds dispersed mid-October [115,117,121,125] Seeds dispersed later usually have lower viability [125].
Cones fall winter Some cones may remain on trees through the next summer [115].
Germination late April through early June [115] Germination roughly coincides with snowmelt and occurs 1-2 weeks before that of associates. Germination occurs earlier on lower elevation or exposed sites and later at upper elevations or in sheltered areas [117].

FIRE ECOLOGY

SPECIES: Larix occidentalis
FIRE ECOLOGY OR ADAPTATIONS: Western larch is considered the most fire-resistant tree in its range [10,17,24,51,89,137]. Fire is an important part of western larch's ecology; without fire or other stand replacing disturbance, western larch will not regenerate successfully and will eventually be replaced by more shade-tolerant species [116].

Fire adaptations: Western larch has many adaptations that enhance its ability to either survive fire or to quickly colonize recently burned areas. While seedlings, saplings, and poles are somewhat susceptible to fire, trees that are 150 to 200 years old or older are able to survive all but the most severe fires [24,116]. It is common for a handful of mature western larch trees to be the sole survivors after fire [24]

Surviving fire: Western larch's extremely thick basal bark protects its cambium from overheating [10,24,48,49,92,116,126,143,155]. Low resin content and light lichen growth also decrease flammability [10,116,143]. Western larch's characteristic high, open crown; open stand habit; and self-pruning lower branches minimize ladder fuels and risk of crown fire [10,24,48,49,59,116,143]. Its deep roots are protected from surface and ground fires [24,49,59,143]. In a synthesis of the literature on northwestern tree species, Minore [93] ranked western larch's bark in the most fire resistant category and its foliage in the least resistant category. He ranked western larch the most fire resistant tree in British Columbia, Washington, Oregon, and Idaho.

Needles of western larch are less flammable than other species' due to their small size. Because they are never more than 5 months old, they maintain a higher water content than other conifers' needles that are replaced every 2 or 3 years [10,24,49,116,143]. Since western larch replaces its needles annually anyway, it is better adapted to defoliation than other conifers. In fact, after defoliation early in the season western larch trees often will produce a 2nd set of needles from heat-resistant woody buds and epicormic branches [10,17,36,48,89]. The small needles also minimize accumulation of surface litter at tree bases [24].

Postburn colonization: Western larch survivors quickly reseed burned-over areas; on mineral soil seedlings develop rapidly and outgrow competitors [10,48,58,85,116,126]. Fire-killed trees may contribute to seeding if fresh cones in the burned crown mature and disperse seed [10]. Seeds are very light and long-winged, allowing trees in nearby stands to reseed even if no onsite seed source is present [10,48]. Since western larch is a very long-lived and fire-resistant species, a potential seed source remains in the area for centuries once it has established [13].

Fire regimes: Wildfires have occurred in western larch forests for over 10,000 years [10,30]. Barrett and others [20] suggest 2 fire regimes for western larch forests: 1) 25-75 year intervals between mixed-severity fires, and 2) 120-350 year intervals between primarily stand-replacing fires. While the species is primarily associated with these regimes, frequent surface fire regimes can also support western larch populations [8]. Frequency and severity of fires vary with elevation, aspect, and habitat type.

Frequent understory fires: Warm, dry sites at the lower elevations of western larch's range in western Montana have been characterized by frequent, low-intensity surface fires occurring at 10 to 30 year intervals. These habitat types include Douglas-fir and grand fir. Stand replacing fires occurred in some of these stands at 150- to 400-year intervals [7,10,60]. 

In ponderosa pine-western larch habitat in Pattee Canyon near Missoula, Montana, fire scars indicate a mean fire return interval of 7.1 years from 1557 to 1918. Fire occurred an average of every 5 to 10 years from 1750 to 1850, and in 10 to 20 year intervals from 1850 through 1900. After 1900, intensity and frequency of fires were reduced until the late 1900s, when high intensity fires swept through north and south slopes of the canyon [60]. 

In the Flathead National Forest of western Montana, underburning occurred on average every 20 to 30 years in even-aged ponderosa pine-western larch stands before 1900, with stand replacing fires occurring at 150- to 400-year intervals. From 1735 to 1900 in the grand fir habitat type of western Montana, an average fire return interval of 17 years (range 3-32) maintained western larch as the most abundant tree followed by lodgepole pine and Douglas-fir. Western larch was also found on 3 Douglas-fir habitat type sites with average intervals of 7 (range 2-28), 16 (range 4-29), and 19 (range 2-48) years [15].

Arno's [8] literature review reported that understory fire regimes prior to 1900 in ponderosa pine-mixed conifer habitat types of western North America favored western larch and other fire resistant species such as ponderosa pine and Jeffrey pine. From 1600 to 1900 in several relict habitat types where western larch occurs in western Montana, fire return intervals averaged 27 (range 17-35) years in the Douglas-fir-big huckleberry (V. membranaceum) type, 25-30 years in the Douglas-fir-dwarf huckleberry (Gaylussacia dumosa) type, and 24 (range 9-42) years in the subalpine fir-queen cup beadlily (Clintonia uniflora) type [7].

Mixed-severity fires: Much of the northern Rocky Mountains are characterized by 30- to 100-year-interval fires of varying severity, which favor open stands of western larch and Douglas-fir in Douglas-fir, western larch, and lodgepole pine habitat types [8,14]. In the Bob Marshall Wilderness, Montana, western larch-Douglas-fir-lodgepole pine and ponderosa pine forest types were historically maintained by mixed severity fire regimes. Many live western larches in this area had 1 to 3 fire scars, and 1 was found with 4 scars. Fire return intervals in this area are nearly twice as long as historic mean intervals [14].

In western larch-Douglas-fir forests of the North Fork of Glacier National Park, Montana, mean fire frequency from 1650 through 1935 was 36 years in relatively dry sites and 46 years in relatively moist sites. In the drier areas, up to 7 understory fires occurred between stand-replacing fires, which occurred at a mean interval of 141 years. Only 1 or 2 understory fires occurred between the less frequent stand-replacing fires (186-year mean intervals) on moister sites [20].

On dry subalpine fir and cool, moist Douglas-fir habitat types that were codominated by western larch, lodgepole pine, and Douglas-fir, average fire return intervals ranged between 30 and 75 years. Severity varied from understory burns to stand-replacing fires [10].

Infrequent stand-replacement fires: In western larch-Douglas-fir forests of northwestern Montana, average fire return intervals from 1735 to 1976 were 120 years in valleys and montane slopes and 150 years for subalpine slopes. Most fires were small and of moderate intensity with occasional patches of high intensity. Though some stands had as many as 6 fires during the period studied, most stands had only 1. A trend of decreasing mean frequency with increasing elevation was noted, and fires on north aspects were more intense and less frequent. Multiple burns occurred primarily on south-facing slopes. In these forests, single burns of low to moderate intensity thinned the overstory and tended to favor regeneration of mixed conifers with patches of seral species, while single intense burns resulted in even-aged forests. Intense, repeated burns (fire return interval <50 years) created shrubfields or homogeneous stands, usually of lodgepole pine [35].

From 1650 to 1935, relatively moist western larch-Douglas-fir forests in Glacier National Park had stand replacement fires at mean intervals of 140 to 340 years [20]. In subalpine fir and Engelmann spruce habitat types in the Middle Fork Drainage of Glacier National Park, Montana, lodgepole pine and western larch stand-replacement intervals were generally 150 to 300 years but as short as 25 years [19], and in grand fir habitat in the Swan Valley of Montana, stand-replacing fires occurred in average 150-year intervals, ranging from less than 20 to more than 300 years [2].

Moist sites of grand fir, subalpine fir, western redcedar, and western hemlock habitat types, which were dominated by western larch, lodgepole pine, Douglas-fir, and Engelmann spruce, burned primarily as stand-replacement fires with average fire return intervals of 120 to 350 years [10].

In western redcedar-hemlock (Tsuga) forests of northern Idaho, fire free intervals ranged from 50 to 100 years with varied intensity. In subalpine fir habitat type, low to medium intensity fires occurred at intervals greater than 150 years [9].

Fire regimes for plant communities and ecosystems where western larch is a common associate are summarized below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
grand fir Abies grandis 35-200 [8]
Rocky Mountain juniper Juniperus scopulorum < 35 [103]
western larch* Larix occidentalis 25-350  [2,4,6,7,8,9,10,14,15,19,20,35,60]
Engelmann spruce-subalpine fir Picea engelmannii-Abies lasiocarpa 35 to > 200 [8]
Rocky Mountain lodgepole pine* Pinus contorta var. latifolia 25-300+ [8,113]
interior ponderosa pine* Pinus ponderosa var. scopulorum 2-30 [8,18,87]
Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [8,11,15]
Oregon white oak Quercus garryana < 35
western redcedar-western hemlock Thuja plicata-Tsuga heterophylla > 200
mountain hemlock* Tsuga mertensiana 35 to > 200 [8]
*fire return interval varies widely; trends in variation are noted in the species summary

POSTFIRE REGENERATION STRATEGY [146]:
Tree without adventitious bud/root crown
Crown residual colonizer (on-site, initial community)
Initial off-site colonizer (off-site, initial community)


FIRE EFFECTS

SPECIES: Larix occidentalis
IMMEDIATE FIRE EFFECT ON PLANT:
Mature western larch trees are more fire-resistant than any other species in their range. (Refer to Fire Ecology or Adaptations for more information.) Unless a smoldering surface fire or ground fire girdles boles or the buds are killed by torching, mature western larch trees will survive all but the most severe fires [10,48,61]. Peterson and Ryan [105] found that death of dormant buds on burned western larch occurred 20% lower on trees than foliage death.

Seedlings and saplings of western larch are readily killed by fire [61]. They are less tolerant than those of ponderosa pine [17,89], but may tolerate low-severity underburning better than white fir (A. concolor), lodgepole pine, or Douglas-fir [155].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
A severe fire in the Bitterroot National Forest, Idaho, killed nearly all grand fir, Douglas-fir, and western redcedar, but most western larch over 8 inches (20 cm) d.b.h. survived [73]. After low-severity surface burns in ponderosa pine forests of eastern Oregon, 64% of western larch showed no negative effects, 33% were scarred at the base with wood exposed, and 2% burned off at the base and were felled. No trees were killed by burning material around the base of the trees [94]. A model presented by Peterson and Ryan [105] predicts zero probability of western larch (13 inches (34 cm) diameter) mortality after fire with a scorch height of 33 feet (10 meters).

PLANT RESPONSE TO FIRE:
Survivors: Young larch that are wounded by surface fires often heal and survive for centuries [10]. Trees defoliated by May slash burning may produce new needles 1 month later, and appear completely recovered within 2 years [49]. One year after underburning shelterwood units in Idaho, western larch overstory mortality was 7% [136]. After prescribed underburning of Douglas-fir-western larch forest in western Montana, western larch's radial growth was reduced in the 1st year postfire, but increased over the following 7 years, suggesting that decreased competition may have enhanced western larch growth [109].

Early Regeneration: Fires that expose mineral soil and reduce competition, especially on north-facing slopes, favor rapid and abundant western larch regeneration and dominance [2,114]. Western larch usually establishes in the 1st season after fire [2], and as much as 5 inches (13 cm) of 1st year postburn seedling growth has been reported after spring, summer, and fall burning of white fir sites on Wallowa-Whitman National Forest, Oregon [104]. In the Flathead National Forest of northwestern Montana, western larch began colonizing both wildfire and prescribed burn sites during the 1st year postfire [133,145]. Burned seedbeds from underburning in shelterwood units in Idaho produced 3 to 7 times more western larch seedlings than unburned seedbeds [136]. After clearcutting in northern Idaho subalpine fir-Engelmann spruce-menziesia type, western larch stocking was 20% on clearcuts that were burned and scarified, compared to 8% stocking on unburned clearcuts [23]. After fires in 1910 and 1919 in Coeur d'Alene National Forest, Idaho, western larch had restocked up to 200 seedlings per acre (500 seedlings/ha) on the north aspect of the study area by the fall of 1923. Western larch seedlings accounted for 83% of conifer seedlings present on all slopes and 88% of those on the north-facing slope [84]. Overstocking may result on some sites if too much mineral soil is exposed [37,67,114,123].

Old skid trails often support high densities of western larch seedlings, but the compacted soil does not allow trees to grow as well as on other sites. Good sites for potential for western larch establishment decrease as regeneration of a burned site progresses [2].

Latham and others [86] found that in general, fires that resulted in open sites, relatively free of vegetation, with full sun, moving shade, and a mineral soil seed bed favored the development of western larch forests. In these conditions, western larch seedlings were generally able to establish quickly and grow taller than other vegetation. Where tree establishment was delayed, however, shrubs were able to establish and suppress western larch.

Competition and Succession: Following fire, western larch must establish rapidly. Insufficient sunlight or exposed mineral soil will delay western larch establishment, allowing development of shrubs or more shade-tolerant tree species [2,148]. If the area does not burn again, shade will prevent western larch regeneration, and other species will eventually replace western larch [85,116]. Generally, stand-replacing fires favor western larch over its competitors because western larch is most likely to survive and postfire survivors will provide an onsite seed source, while less fire-resistant competitors must rely on offsite sources or unburned islands [1,10,135]. Low to moderate intensity fires thin out competitors [10,30]. The species may dominate the area for 150-350 years in the absence of fire [10,135].

Western larch and lodgepole pine are early seral species that often compete in the same recently burned areas. In general, lodgepole pine performs better on drier or more exposed sites [135]. Due to western larch's later age of 1st seed production and longer lifespan, it may be favored over lodgepole pine on sites that burn less frequently [138]. Western larch-lodgepole pine stands in grand fir sites of northwestern Montana with as little as 10% western larch overstory can eventually be dominated by western larch [1]. In Coram Experimental Forest in northwestern Montana, single high intensity burns in western larch-Douglas fir habitat thinned the overstory and favored regeneration of western larch, Douglas-fir and lodgepole pine, while multiple severe burns tended to promote lodgepole pine [138]. Western larch benefits from periodic surface fires that kill competing shade-tolerant conifers [15].

Absence of fire: Prior to 1900, fire maintained western larch as a dominant seral species in various habitats [3,7]. Lack of periodic fires may limit western larch regeneration [37]. Fire suppression in last century has favored thickets of suppressed shade-tolerant conifers [4,7,10], which result in a decline in the vigor of all trees [10]. These sites are at risk of high-intensity wildfires [3,4,60]. Large areas in and around the western larch habitat type are now characterized by such crowded and stagnant stands [10], and fire suppression has been linked to the decline of western larch habitat in Idaho, Montana, Oregon, and Washington [10,30,60,91].

In Bear Creek Canyon of the Bitterroot Mountains, Montana, where the old western larch are prevalent and younger ones less abundant and dwarf mistletoe has infected most trees, the species is near extinction due to lack of fire or other disturbance [91]. Remaining old-growth ponderosa pine-western larch habitat in Pattee Canyon near Missoula, Montana, has a thick understory of Douglas-fir saplings and pole-sized trees. This understory could provide ladder fuels, resulting in a crown fire [60]. If fire does not occur before the remaining trees die in these areas, or if ladder fuels create a crown fire that burns intensely enough to kill the remaining trees, the western larch seed source may be eliminated. However, if a seed source remains after fire, western larch may thrive in the postfire mineral seedbed with reduced competition.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Regeneration of western larch after fire depends on site conditions and fire intensity. After moderate fires in grand fir habitat of the Blue and Wallowa mountains of northeastern Oregon, western larch in cool, moist areas had increased by the 1st and the 5th years. After severe fires, the species decreased after the 1st year, but increased by postfire year 5. In warm, dry grand fir habitats, moderate fires resulted in a decrease after the 1st year and no change by the 5th year postfire, while severe fires caused a decrease in western larch after the 1st year and an increase by 5 years postfire. Western larch's response to burning in several grand fir associations was [75]:

Plant Association Fire Severity Western larch % cover Notes
Prefire 1st postfire year 5th postfire year 10th postfire year ----
grand fir-beadlily (Clintonia uniflora) severe ---- 2 5 ---- fire killed all trees
grand fir-twinflower (Linnaea borealis) moderate 15 5 5 ---- ----
grand fir-grouse huckleberry severe ---- 0 ---- 13 (range 0-30) fire killed all trees
grand fir-grouse huckleberry moderate ---- 0 0 ---- ----

In early postfire succession in the northern portion of the Bitterroot Mountains, Montana, western larch formed nearly pure stands on north and east exposures, and western white pine and Douglas-fir replaced western larch in the absence of fire in 1929 [85]. Historically, following intense stand-replacing fires in mesic to moist habitats of the northern Rocky Mountains, even-aged western larch stands often developed, while in drier habitats, western larch was maintained by frequent surface fires that minimized competition [1,61].

In ponderosa pine-Douglas-fir forests of the inland northwest, the FIRESUM model predicts successful regeneration of ponderosa pine with a 10- to 20-year fire return interval. More severe fires at 50-year intervals predict western larch dominance for 150 years, then an increase in ponderosa pine, and Douglas-fir dominance after 200 years. Without fire, Douglas-fir would dominate the understory and eventually the overstory, limiting regeneration of western larch and ponderosa pine [77].

For further information on western larch response to fire, see Fire Case Studies. The Research Project Summary Vegetation response to restoration treatments in ponderosa pine-Douglas-fir forests of western Montana provides information on prescribed fire use and postfire response of plant community species including western larch.

FIRE MANAGEMENT CONSIDERATIONS:
Fire is an important management practice for maintaining western larch [10,30,60,91]. Ideally, prescribed burns should expose well-distributed patches of mineral soil and reduce sprouting potential of competitors [67,114,123]. However, even areas with very little burned surface result in significantly better western larch regeneration than unburned sites [10,130]. In good seed crop years, overstocking may result in mesic habitats where too much mineral soil is exposed, and thinning may be necessary to facilitate a vigorous stand [37,67,114,123]. Harsh sites with poor regeneration potential may require planting after burning [10,37].

Norum [67,97] provides detailed recommendations for prescribed burning in western larch-Douglas-fir forests. Based on studies of fire and harvest regimes, Antos and Shearer [2] make recommendations for management practices on grand fir-queencup beadlily habitat type in northwestern Montana.

Timing and Site Conditions: The timing of prescribed burns is important for western larch site preparation; large fuels should be dry and soil moisture low in order to expose mineral soil [10,37,97,99,123]. Norum [98] reported that 10 to 17% water content in small diameter (<4 inch (<10 cm)) fuels is a safe and effective range for burning in western larch-Douglas-fir habitat. Spring and early summer fires usually burn only the surface of the duff layer, while late summer or early fall fires after dry summers tend to be more effective at exposing enough mineral soil for larch regeneration. August or early September, before the fall rains, are the best times for burning north-facing slopes, but on other aspects, there is more flexibility for timing a successful burn [10,37,97,99,123]. Timing of seed dispersal should also be considered when planning fall fires; burning before seedfall is preferable [37]. Depending on site conditions, removing duff from bases of western larch trees to prevent cambium and root damage and/or thinning understory to reduce ladder fuels may be necessary prior to burning [16,67,123].

Fire Intensity: An adequate seedbed for western larch usually results from moderate intensity fires in dry duff. High intensity fires may expose too much mineral soil and result in overstocking [10,37]. Prescribed burning after clearcutting or shelterwood cutting is sometimes used to mimic the effects of severe wildfires on western larch habitat [10,148].

While western larch seedlings usually establish best on severely burned sites [109], underburning may lead to consistent successful natural regeneration but requires careful attention to fuel and site conditions [10,96,104,114]. Harvey and others [69] found burning to remove slash reduced ectomycorrhizal activity after partial cuts in western larch-Douglas-fir forests of northwestern Montana. They recommend against burning to remove slash on harsh sites where understory competition may limit conifer germination or where soil organic matter is low. They suggest underburning is better suited for areas where excessive regeneration is expected or where understory vegetation is desired, especially if burn conditions are chosen to limit duff reduction, which in turn will limit conifer (including western larch) germination.

Models: Reinhardt and Ryan [109,110] present a model for predicting postfire mortality of western larch and 6 other western conifers using bark thickness and percent crown volume. Desired levels of mortality can be predicted using tree species, diameter, height and crown ratio, and maximum allowable flame length. FIRE-BCG simulates fire succession on coniferous forest landscapes of the northern Rocky Mountains, including western larch habitat [78], and FIRESUM models tree establishment, growth, mortality, fuel accumulation, fire behavior, and fuel reduction in ponderosa pine/Douglas-fir forests of the inland northwest [77].


FIRE CASE STUDIES:

SPECIES: Larix occidentalis

1st CASE STUDY:
FIRE CASE STUDY CITATION:
Crane, M. F., compiler. 1991. Western larch/Douglas-fir prescribed fire on the Lubrecht Experimental Forest, Montana. In: Larix occidentalis. 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/ [ ].

REFERENCES:
Norum, Rodney A. 1975. Characteristics and effects of understory fires in western larch/Douglas-fir stands. Missoula, MT: University of Montana. 155 p. Dissertation. [95].

Norum, Rodney A. 1976. Fire intensity-fuel reduction relationships associated with understory burning in larch/Douglas-fir stands. In: Proceedings: Montana Tall Timbers fire ecology conference and fire and land management symposium; 1974 October 8-10; Missoula, MT. No. 14. Tallahassee, FL: Tall Timbers Research Station: 559-572. [94].

Norum, Rodney A. 1977. Preliminary guidelines for prescribed burning under standing timber in western larch/Douglas-fir forests. Res. Note INT-229. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 15 p. [97].

Reinhardt, Elizabeth D.; Ryan, Kevin C. 1988. Eight-year tree growth following prescribed underburning in a western Montana Douglas-fir/western larch stand. Res. Note INT-387. Ogden, UT: U.S. Department of Agriculture, Forest Service. 6 p. [109].

Stark, Nellie M. 1977. Fire and nutrient cycling in a Douglas-fir/larch forest. Ecology. 58: 16-30. [142].

Stark, N.; Steele, R. 1977. Nutrient content of forest shrubs following burning. American Journal of Botany. 64(10): 1218-1224. [141].

SEASON/SEVERITY CLASSIFICATION:
Spring and fall/low to moderate severity

STUDY LOCATION:
The study site is on the University of Montana Lubrecht Experimental Forest located 41 miles (66 km) east of Missoula, Montana, in the Garnet Mountains.

PREFIRE VEGETATIVE COMMUNITY:
Study plots were in a Douglas-fir (Pseudotsuga menziesii)-dwarf huckleberry (Vaccinium caespitosum) habitat type, bearberry (Arctostaphylos uva-ursi) phase. Overstory trees ranged in age from 50 to 300 years with an average diameter of about 8.6 inches (22 cm). This stand was not vigorous and was composed primarily of Douglas-fir and western larch (Larix occidentalis) with small amounts of lodgepole pine (Pinus contorta) and ponderosa pine (P. ponderosa). The largest and best trees had been selectively logged about 50 years earlier. Subsequently, an uneven understory of dense Douglas-fir had developed. There were a large number of widely spaced, large-diameter western larch stumps to indicate preharvest conditions. In addition to conifers and bearberry, huckleberries (Vaccinium spp.), white spirea (Spiraea betulifolia), and heartleaf arnica (Arnica cordifolia) were common in the understory [95,109,142].

TARGET SPECIES PHENOLOGICAL STATE:
Western larch's phenological state can be inferred based on timing of the burns. Fires occurred from May through October, so western larch's phenological state would have been varied. During the May through July burning period, needle growth would have been ending, diameter growth would occur, and height growth would have peaked near the end. Pollination and fertilization would have occurred during this time period. By the August and September burns, tree growth for the year would have been complete, and cones would have been mature. Most seed dispersal would have occurred during the burning period. Western larch phenology is described in more detail in Seasonal Development.

SITE DESCRIPTION:
The site is located at about 4,800 feet (1,464 m) with east to northeast exposures and slopes of 20 to 50%. The area has warm summers and cold winters with annual precipitation of about 18 inches (470 mm), most of which falls as winter snow. Soils in the area are thin, poorly developed sandy loams in the Holloway Series [96]. They formed in residuum weathered from quartzite, argillite and, on these sites, contain sufficient rock to be considered talus slopes. Calcium and phosphate are limited in these soils [142]. The site had a substantial complex fuel load including many dead small trees in understory thickets. Total dead fuel loadings ranged from 5.5 to 50 tons per acre (12.3-112.1 metric tons/ha). Over 100 parameters were measured in connection with these fires [141].

FIRE DESCRIPTION:
Out of the 20 test plots broadcast burned during 1973, 9 were burned from early May to the 1st of July. The rest were burned from early September to mid-October. The average dead fuel moisture contents ranged from 8.5 to 35% and wind speeds were from 0 to 15 miles per hour (0-24 km/hr). Strip ignition horizontally across plots was used for most plots, and fire intensity on each strip was allowed to drop before the next strip was ignited [96].

FIRE EFFECTS ON TARGET SPECIES:
Stark and Steele analyzed prefire and postfire nutrient content of soil, soil water, and plants. Three years after the fires, average cover of western larch in the study area was as follows: 0.27% on lightly burned plots, 0.23% on moderately burned plots, 2.4% on intensely burned sites, and no western larch seedlings had established on control plots. Results of nutrient comparisons from aboveground samples of western larch seedlings from burned and control plots were [141]:

  Control Hot burn
Calcium (/g) 4,805 3,000
Copper (/g) 37 18
Iron (/g) 162 280a
Potassium (/g) 6,864 16,000a
Magnesium (/g) 967 1,300a
Manganese (/g) 343 198
Sodium (/g) 114 95
Phosphorus (/g) 4,457 7,190a
Zinc (/g) 28 37a
(a) indicates a significant difference at the 5 % level.

Eight years after the fires an analysis of radial and basal area growth was performed. Western larch's relative radial increment on burned plots was less than on unburned plots in the 1st year and greater on burned plots thereafter. The difference in growth of trees on burned plots compared to trees on control plots increased each year for the 1st 4 years. Western larch's response was more positive than that of Douglas-fir, and from the 4th to the 8th year the average relative radial increment was 60 to 80% greater on burned plots than on unburned plots. The average unadjusted radial growth increment of trees on burned and unburned plots for the 1st 8 years after treatment is given below [109]:

Year Burned Unburned
  inch cm inch cm
1 0.044 0.114 0.048 0.121
2 0.059 0.150 0.054 0.136
3 0.076 0.193 0.055 0.139
4 0.069 0.175 0.036 0.091
5 0.068 0.173 0.037 0.093
6 0.056 0.143 0.034 0.087
7 0.067 0.171 0.037 0.093
8 0.071 0.181 0.042 0.106

FIRE MANAGEMENT IMPLICATIONS:
Underburning in similar western larch-Douglas-fir forests is feasible [96]. An average of 15% of the overstory trees were killed in the plots. Within the range of fuel loadings in this study, fires were most manageable and still effective when the moisture content of 0 to 1 inch (0-2.5 cm) dead fuels was around 15% [95]. Strip ignition helped overcome control and ignition problems caused by discontinuous concentrations of heavy fuels. Underburning requires attention to the form, moisture status, and amount of living vegetation [96,97].

Western larch seedlings established best on sites burned by the hottest fires. Prescribed underburns in western larch stands can result in an increase in individual tree relative radial increment. However, growth of western larch in these poorly growing stands continued to be slow. Growth, even in trees with fire damage, was not reduced by the fire, and fire may be a useful tool for fuel reduction or other purposes in such stands [109].


2nd CASE STUDY:
FIRE CASE STUDY CITATION:
Scher, Janette S., compiler. 2002. Prescribed fire and wildfire in western larch forests on Miller Creek-Newman Ridge, Montana. In: Larix occidentalis. 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/ [ ].

REFERENCES:
Beaufait, William R.; Hardy, Charles E.; Fischer, William C. 1977 [Revised]. Broadcast burning in larch-fir clearcuts: The Miller Creek-Newman Ridge study. Res. Pap. INT-175. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 53 p. [21].

DeByle, Norbert V. 1981. Clearcutting and fire in the larch/Douglas-fir forests of western Montana--a multifaceted research summary. Gen. Tech. Rep. INT-99. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 73 p. [37].

DeByle, Norbert V.; Packer, Paul E. 1972. Plant nutrient and soil losses in overland flow from burned forest clearcuts. National Symposium on Watersheds in Transition. 1972: 296-307. [38].

Latham, Penelope A.; Shearer, Raymond C.; O'Hara, Kevin L. 1998. Miller Creek Demonstration Forest--A forest born of fire: a field guide. Gen. Tech. Rep. RMRS-GTR-7. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 68 p. ( book + 2 supplements and 2 posters). [86].

Norum, Rodney A. 1981. Fire behavior and effects. In: DeByle, Norbert V., ed. Clearcutting and fire in the larch/Douglas-fir forests of western Montana - A multifaceted research summary. Gen. Tech. Rep. INT-99. Ogden, UT: U.S. Department of Agriculture, Forest Service, intermountain Forest and Range Experiment Station: 17-18. [98].

Shearer, Raymond C. 1975. Seedbed characteristics in western larch forests after prescribed burning. Res. Pap. INT-167. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 26 p. [123].

Shearer, Raymond C. 1976. Early establishment of conifers following prescribed broadcast burning in western larch/Douglas-fir forests. In: Proceedings, Tall Timbers fire ecology conference and fire and land management symposium; 1974 October 8-10; Missoula, MT. No. 14. Tallahassee, FL: Tall Timbers Research Station: 481-500. [124].

Shearer, Raymond C. 1981. Silviculture. In: DeByle, Norbert V., ed. Clearcutting and fire in the larch/Douglas-fir forests of western Montana--a multifaceted research summary. Gen. Tech. Rep. INT-99. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station: 27-31. [127].

Shearer, Raymond C. 1982. Establishment and growth of natural and planted conifers 10 years after clearcutting and burning in a Montana larch forest. In: Baumgartner, David M., ed. Site preparation and fuels management of steep terrain: Proceedings of a symposium; 1982 February 16-16; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 149-157. [128].

Shearer, Raymond C. 1984. Effects of prescribed burning and wildfire on regeneration in a larch forest in northwest Montana. In: New forests for a changing world: Proceedings, Society of American Foresters convention; 1983 October 16-20; Portland, OR. Washington, DC: Society of American Foresters: 266-270. [129].

Shearer, Raymond C. 1989a. Fire effects on natural conifer regeneration in western Montana. In: Baumgartner, David M.; Breuer, David W.; Zamora, Benjamin A.; [and others], compilers. Prescribed fire in the Intermountain region: Symposium proceedings; 1986 March 3-5; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 19-33. [130].

Shearer, R. C. 1989b. Seed and pollen cone production in Larix occidentalis. In: Turnbull, J. W., ed. [Title of larger work unknown]. 1989 August 21-24; Queensland, Australia. ACIAR Proceedings No. 28. Canbiera, Australia: Australian Centre for International Agricultural Research: 14-17. [120].

Shearer, Raymond C.; Stickney, Peter F. 1991. Natural revegetation of burned and unburned clearcuts in western larch forests of northwest Montana. In: Nodvin, Stephen C.; Waldrop, Thomas A., eds. Fire and the environment: ecological and cultural perspectives: Proceedings of an international symposium; 1990 March 20-24; Knoxville, TN. Gen. Tech. Rep. SE-69. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station: 66-74. [133].

Stickney, Peter F. 1982. Initial stages of a natural forest succession following wildfire in the northern Rocky Mountains, a case study. Unpublished report on file with: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. 2 p. [145].

Tonn, Jonalea R.; Jurgensen, Martin F.; Graham, Russell T.; Harvey, Alan E. 1995. Nitrogen-fixing processes in western larch ecosystems. In: Schmidt, Wyman C.; McDonald, Kathy J., compilers. Ecology and management of Larix forests: a look ahead: Proceedings of an international symposium; 1992 October 5-9; Whitefish, MT. Gen. Tech. Rep. GTR-INT-319. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 327-333. [150].

SEASON/SEVERITY CLASSIFICATION:
May through October/low to very severe

STUDY LOCATION:
Two study locations were used. The first contained 641 acres in the Miller Creek and Martin Creek drainages of the Flathead National Forest of northwestern Montana. This is referred to as the Miller Creek area. The second location consisted of 526 acres on Newman Ridge located between Two Mile Creek and Ward Creek on the Lolo National Forest near the border of western Montana and Idaho.

PREFIRE VEGETATIVE COMMUNITY:
Miller Creek: The dominant conifers at Miller Creek were western larch (Larix occidentalis), Douglas-fir (Pseudotsuga menziesii), and Engelmann spruce (Picea engelmannii), with some lodgepole pine (Pinus contorta), grand fir (Abies grandis), and subalpine fir (A. lasiocarpa). The western larch-Douglas-fir cover type occupied over 50% of the area, and western larch composition was 26%. Most of Miller Creek was considered to be in one of three phases of the subalpine fir-queencup beadlily (Clintonia uniflora) habitat type. Habitat types identified at Miller Creek are [21,37,124,130,133]:

Habitat Type Location
subalpine fir-queencup beadlily type, menziesia (Menziesia ferruginea) phase higher middle and upper north- and east-facing slopes
subalpine fir-queencup beadlily type, common beargrass (Xerophyllum tenax) phase drier south and west aspects
subalpine fir-queencup beadlily type, queencup beadlily phase most other sites
western redcedar (Thuja plicata)-queencup beadlily type stream bottoms

Newman Ridge: Dominant conifers at Newman Ridge were Douglas-fir, western larch and lodgepole pine with some ponderosa pine (Pinus ponderosa), grand fir, subalpine fir, western white pine (P. monticola), Engelmann spruce and western redcedar. Prefire stands at Newman Ridge were 26% western larch. The 7 habitat types identified on Newman Ridge are [21,37,124,130]:

Habitat Type Location
Douglas-fir-ninebark type (Physocarpus malvaceus) convex southwest slopes
grand fir-queencup beadlily type concave east, northwest, and protected south-facing slopes
grand fir-common beargrass type upper west-facing slopes
western redcedar-queencup beadlily type, menziesia phase concave north- and northeast-facing slopes
Douglas-fir-dwarf huckleberry type (Vaccinium caespitosum), common beargrass phase upper south-facing slopes
subalpine fir-queencup beadlily type, menziesia phase north slopes along the ridge
subalpine fir-common beargrass type, dwarf huckleberry phase south slopes near the ridge

TARGET SPECIES PHENOLOGICAL STATE:
Western larch's phenological state can be inferred based on the timing of the burns. Fires occurred from May through October, so western larch's phenological state would have been varied. At the time of the earliest burns western larch needle growth would have been ending and diameter growth commencing. Pollen and seed cones would be apparent, and pollination may have been occurring. The latest October burns would have occurred when tree growth was complete for the season, and seed dispersal probably would have been complete. Western larch phenology is described in more detail in Seasonal Development.

SITE DESCRIPTION:
A total of 76 treatment plots were established at the 2 sites, with an equal number of sites facing each of the 4 cardinal directions. Miller Creek had 60, 10-acre (4-ha) units, and Newman Ridge had 16 units, ranging in size from 20 to 58 acres (8-24 ha). Prior to fire treatment, most study plots were clearcut and slashed between 1966 and 1969. Other sites were left uncut for comparison.

Miller Creek: Elevation at Miller Creek ranges from 4,200 to 5,000 feet (1,280-1,524 m) with slopes averaging 24% and ranging from 9 to 35%. Soils are Andic Cryoboralfs that developed in glacial till from the argillites and quartzites of the Wallace (Belt) formation. Average precipitation is about 25 inches (640 mm) annually; approximately two-thirds falls as snow during the long, cool winter [37,38,124,130].

Newman Ridge: Elevation at Newman Ridge ranges from 4,400 to 5,400 feet (1,341-1,646 m) with slopes averaging 55% and ranging from 44 to 76%. Soils are Andic Cryochrepts that have developed in place or in colluvium from argillites and quartzites of the Belt formation. There is a surface loess deposit containing ash from the Mt. Mazama and Glacier Peak volcanic eruptions at both sites which is 0.5 to 2.5 inches (1-6 cm) thick at Miller Creek and 2 to 3 inches (5-8 cm) thick at Newman Ridge. Average precipitation is nearly 40 inches (1020 mm) at Newman Ridge of which two-thirds falls as snow[37,70,130].

Fuel loads: Duff depth averaged 2.2 inches (5.5 cm) at Miller Creek and 2.1 inches (5.2 cm) at Newman Ridge, with deeper duff on north and east exposures than on south and west aspects. Fuel loads after clearcutting and before fire, excluding duff, ranged from 60 to 165 tons per acre (135-370 T/ha), but were generally uniform within each size class. Fuel loads at the Miller Creek sites were slightly higher than at Newman Ridge. Mean weights of fuel loads by size class are as follows [21]:

Down and dead stem and branchwood components
Site Duff Needles 0-1 cm 1-10 cm > 10 cm Total
Miller Creek (tons/acre) 26.3 1.5 1.3 9.8 101.3 140.3
Newman Ridge (tons/acre) 22.9 1.4 1.1 10.7 90.5 126.5

FIRE DESCRIPTION:
Prescribed burns: Slash fuels were allowed to cure for an average of 9 months before burning (range: 2-18 months) [21,130]. Prescribed burns were conducted in the spring, summer, and fall of 1967 and 1968 at Miller Creek and in 1969 and 1970 at Newman Ridge [21,37,129,130]. Fires were ignited by center-firing, by flanking, or by a combination of these, and most fires were ignited in late afternoon or evening after winds had decreased [37,98]. Due to concern about fire control, clearcuts with heavier fuel loads were burned under wetter conditions [37]. Burning patterns and fire severity varied among the plots burned. After broadcast burns at Miller Creek, 75% of the fuels less than 3.9 inches (10 cm) burned and 60% of the larger fuels burned. At Newman Ridge 89% of the fuels less than 3.9 inches (10 cm) burned and 55% of the larger fuels burned [21]. Greater surface soil heating occurred at Newman Ridge than at Miller Creek because the duff layer was shallower and water content of both duff and soil was lower. The average duff reduction ranged from 36 to 70% at Miller Creek and 44 to 99% at Newman Ridge [37,124].

Wildfires: On August 23, 1967, a wildfire burned 5 units that had been clearcut and 4 units that were uncut forest at Miller Creek [37,129]. Average duff reduction from the wildfire was 93% with a range of 84 to 100%; all overstory and understory trees were killed and shrubs and herbs were burned to the ground [145]. Fuel moisture of 0 to 0.4 inch (0-1 cm) branchwood ranged from 6 to 21% [21]. A wildfire occurred at Newman Ridge on July 25, 1969 [130].

FIRE EFFECTS ON TARGET SPECIES:
Seedbed condition: Seedbeds after the fires varied. Early 1967 and most 1968 fires did not completely burn litter and duff or expose much mineral soil. The 1967 wildfire consumed most of the duff and killed most roots of sprouting species. Other fires were spotty and exposed some mineral soil [19]. Unburned duff continued to decrease for several years, exposing bare soil on areas where the fire had left charred duff. The reasons for this decrease may include: increased decomposition stimulated by warmer surface temperature during May and June where adequate moisture was present; redistribution by precipitation, runoff or wind; and oxidation. However, since western larch needs to establish quickly and become dominant, continued duff reduction may benefit other conifer species more.

Seed Supply: Clearcutting and burning eliminated onsite seed sources [133]. Nearby uncut trees, onsite survivors (uncut stands only), and scorched cones from fire-killed trees provided the postfire seed source [129]. In addition to natural seeding, seeds were sown in 1967 on test plots, and bareroot seedlings were planted on Newman Ridge from 1970 through 1975 and on 4 clearcuts at Miller Creek from 1970 through 1973. Postfire seed dispersal into the clearcuts from western larch in the timber around clearcut areas was good. The best seed year for all conifers was 1971; however, heavy frost in May of that year decreased the potential western larch seed crop [124,130]. Another good crop occurred in 1980 [130]. Seed fall was highest on south-facing clearcuts, followed in order by west, east, and north aspects [127]. The cumulative average number of sound seed of western larch from 1969 through 1974 on 8 clearcuts on Newman Ridge by distance from the source is listed below [127,128]:

Within timber Distance from timber edge within clearcut
 

Within timber

0-200 ft (0-61 m)  200-400 ft (61-122 m) 400-600 ft (122-183 m) 600-800 ft (183-244 m)
Sound seed per acre 53,200 7,500 3,700 2,000 800
Sound seed per ha 131,500 18,600 9,200 4,900 1,900

Germination and growth: Fire influenced the amount and height of natural regeneration. Germination of western larch began the 1st year after fire several days before snow completely melted, and was greater on mineral soil than on unburned duff over 0.5 inches (13 mm). Depending on the site, early succession associates were fireweed (Epilobium angustifolium), Scouler willow (Salix scouleriana), snowbrush ceanothus (Ceanothus velutinus), Douglas-fir, subalpine fir, and/or lodgepole pine [133,145]. Despite an adequate seed source, very few western larch seedlings established on unburned duff [123,127,129].

In 1978 at Miller Creek, stocking of established western larch seedlings averaged 54% on burned units and 5% on unburned clearcuts, and by 1984 stocking averaged 71% on burned units and 1% on unburned clearcuts [129,130]. Western larch seedlings outnumbered other conifers on 10 of 18 units. By 1984 western larch had stocked well on all Miller Creek aspects but had the highest stocking on west-facing slopes [130]. On 7 Miller Creek sites studied on south and east slopes, western larch regeneration decreased from 1974 through 1984 while regeneration of other conifers more than doubled [133].

Natural regeneration of western larch at Newman Ridge was lower than at Miller Creek due to harsh site conditions, larger clearcuts, and poor seed production [130]. In 1979 at Newman Ridge, stocking of established western larch seedlings averaged 10% (6%-16%) on burned clearcuts [128]. Expected survival for planted western larch on such sites at Newman Ridge was high in the western redcedar-queencup beadlily habitat type; moderate in the grand fir-queencup beadlily, grand fir-common beargrass, and Douglas-fir-dwarf huckleberry habitat types; and low in the Douglas-fir-ninebark habitat type. Actual survival by 1979 was lower than expected, only 38% for western larch overall [129,130]. Stocking was best on north-facing slopes at Newman Ridge [130].

The average number of established (>1 foot (30.5 cm) tall) western larch seedlings in 1979 and 1984 and the range in 1984 on 37 burned units at Miller Creek and 7 burned clearcuts at Newman Ridge are given below [130]:

1979 mean 1984 mean 1984 range
Miller Creek
Seedlings per acre 610 931 92-4,003
Seedlings per ha 1,507 2,301 227-9,892
Newman Ridge
Seedlings per acre 30 91 10-228
Seedlings per ha 74 225 25-563

At Newman Ridge in 1979, the tallest western larch seedlings averaged 3.0 feet (0.9 m) [128]. At Miller Creek in 1978, the tallest western larch seedlings averaged 8.5 feet (2.6 m) on uncut plots burned by the wildfire, which was significantly greater than the average of 5.3 feet (1.6 m) on clearcuts that were burned by the wildfire. This average was significantly greater than the average height of 3.7 feet (1.1 m) on clearcuts that were burned by prescribed fire in 1967. This sequence may be because the uncut units burned by wildfire had a greater proportion of older western larch. Another possible explanation was that the presence of shade-killed trees may have decreased evapotranspiration and increased the number of growing days.

Height was also related to habitat type and phase with the tallest trees on the warmer and drier common beargrass phase of the subalpine fir/queencup beadlily habitat type and shorter trees on the cooler and moister menziesia phase. Trees were significantly taller on east and south aspects than on west or north aspects. The tallest western larch trees in 1978 were on uncut stands burned by wildfire. Evidently, soil moisture is not as limiting in early stand development as it is later; also, trees on the warmer sites began growth earlier in the spring and may have benefited from extra nitrogen contributed by snowbrush ceanothus [129].

Thirty years after the fires, basal area of western larch regeneration was greater than that of all other tree species in the common beargrass phase. In the menziesia phase, western larch had the highest basal area in the prescribed burn treatments as well as in treatments that were clearcut and burned by wildfire. Lodgepole pine had higher basal area in the uncut wildfire plots [150].

Mortality: Seed and seedling losses were caused by rodents, drought, frost heaving, high temperatures at the soil surface, and migrating dark-eyed juncos that ate emerging seedlings in 1968 [86,124,127,129]. Drought was the leading cause of death on south-facing slopes and 2nd highest on other aspects. The average survival of larch plantations in Newman Ridge was 38% 10 years after treatment [128].

FIRE MANAGEMENT IMPLICATIONS:
In general, fires that resulted in open sites relatively free of vegetation with full sun, moving shade, and a mineral soil seed bed favored the development of western larch forests. In these conditions, western larch seedlings were generally able to establish quickly and grow taller than other vegetation before being shaded out. Where tree establishment was delayed, shrubs were able to establish and suppress western larch [86].

During late spring and early summer, duff is usually wet, and fires do not expose much mineral soil. Late summer or early fall fires (on south, east, and west slopes) are more effective at removing duff and exposing mineral soil for western larch regeneration. On north-facing slopes, summer burning before the fall rains is probably best [37,123]. However, if precipitation occurs, fuels and duff need to dry for several days. At Newman Ridge, moderate intensity fires removed most of the duff and prepared an adequate seedbed. At Miller Creek, the same intensity fire exposed less mineral soil because the duff was thicker and wetter.

Habitat type and site conditions alter the amount of duff removal needed for western larch regeneration. On mesic habitat types severe fires that expose a high proportion of mineral soil, followed by good seed years, lead to dense stocking. On steeper slopes with drier conditions, such as at Newman Ridge, residual duff layers have an adverse impact on the survival of seedlings.

Seed dispersal should be taken into account when deciding the time of fall fires. In a plentiful seed year, dispersed seed could be destroyed by fires after early September at lower elevations and a few weeks later at higher elevations. The light seeds of western larch enable it to establish a high proportion of the seedlings in the center of larger clearcuts such as those on Newman Ridge. Planting, rather than seeding, may be necessary for reforestation on steep, harsher sites [37].


MANAGEMENT CONSIDERATIONS

SPECIES: Larix occidentalis
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Larch forests provide food and cover for a wide range of fauna. Rodents eat seeds and seedlings, birds forage for insects and nest in western larch, and squirrels often cut and cache cones. Deer, elk, and moose browse larch, though probably only as a last resort, and black bears forage on sugars that are concentrated in the sap layer in the spring [117,131].

Several studies have investigated the importance of western larch forests to woodpeckers. McClelland [90] found that pileated woodpeckers, a sensitive species dependent on old-growth western larch forests, used 17 times more western larch trees than Douglas-fir even though Douglas-fir trees were 5 times more abundant. Hadfield and Magelsson [62] reported all western larch trees in their 5-year postburn study showed signs of woodpecker foraging, and most feeding occurred in 1st year after tree death. After stand replacing fires in conifer forests of the northern Rocky Mountains, Hutto [74] found evidence of woodpecker foraging on 64% of western larch trees larger than 3.9 inches (10 cm) d.b.h. compared with 81% of ponderosa pine, 48% of Douglas-fir, 2.3% of Engelmann spruce, and 0.2% of lodgepole pine.

Palatability/nutritional value: Western larch appears to be unpalatable to most big game animals, but it is eaten as emergency food [115,117]. Its seeds are palatable to small birds and mammals, although larger seeds are preferred [131]. Larch needles provide a major source of food to several species of grouse [12].

Nutrient values for western larch needles, twigs, and other tree parts have been reported from 2 sites in western Montana [140]. Whole tree values have also been published [139]. Western larch needles at two locations in eastern Washington contained 2.0% and 1.7% nitrogen, respectively [57]. Green needles from Lubrecht Experimental Forest in western Montana, had a mean ash content of 5.8% with a range of 3.47 to 8.16%, and those from Coram Experimental Forest, Montana, had mean ash content of 5.3% with a range of 4.9 to 8.9%. The following table summarizes nutrient values for needles from these 2 sites [140].

  Lubrecht mean Lubrecht range Coram mean Coram range
Calcium (g/g) 3,031 2,000-4,800 2,213 1,980-2,390
Copper (g/g) 8.3 5.0-15.2 15.5 10.7-35.2
Iron (g/g) 86.8 41-173 126 109-218
Potassium (g/g) 6,405 2,800-9,760 4,958 4,390-5,388
Magnesium (g/g) 1,098 692-1,592 1,083 1,005-1,113
Manganese (g/g) 216 81-405 181 160-239
Nitrogen (g/g) 13,518 9,730-15,540 23,320 17,920-28,923
Sodium (g/g) 61.4 24.4-123.0 56 45-125
Phosphorus (g/g) 2,343 1,678-3,189 2,960 1,894-3,269
Zinc (g/g) 15.8 6.0-35.6 24.6 21.1-27.7

Cover value: Woodpeckers and other cavity nesters utilize western larch. Around its decaying interior, a dead western larch tree retains a protective layer of sapwood, which provides nesting, roosting, and feeding opportunities. Flying squirrels, woodpeckers, owls, and various songbirds nest in rotting western larch cavities. Snags are used by osprey, bald eagles, and Canada geese for nesting [12], and raptors may nest in brooms of trees infected with dwarf mistletoe [25].

VALUE FOR REHABILITATION OF DISTURBED SITES:
Western larch performs well on sites disturbed by fire, as well as on sites disturbed by shelterwood, seed tree, and clearcut logging methods followed by prescribed burning or scarification [46,58,114,116]. However it does not compete well with grasses and shrubs [114]. Fiedler [46] describes how to estimate regeneration probabilities for various habitat type and site preparation combinations. Research on western larch indicates that artificial regeneration by bare root, container, and seed may be possible on a large scale [41,154].

OTHER USES:
Wood Products: Western larch is one of the most important timber-producing species in the western United States and western Canada. It has the densest wood of the northwestern conifers and is also very durable and moderately decay-resistant. Its high heating value makes it one of the best fuel woods in the region. The wood is also used commercially for construction framing, railroad ties, pilings, mine timbers, interior and exterior finishing, and pulp, and burned snags are often used to make shakes [12,50,72,115,154]. High sugar content of western larch makes it undesirable for concrete forms because the sugars react chemically with the concrete [117]. Faurot [43] describes methods for estimating total volumes of western larch wood, wood residue, and bark.

Non-wood uses: Native Americans used western larch for treatment of cuts and bruises, tuberculosis, colds and coughs, sore throats, arthritis, skin sores, cancer, and for blood purification [68,153]. They also made syrup from the sap, ate the cambium, and chewed solidified pitch as gum [68]. Arabinogalactan, the gum from the tree, is used for lithography and in food, pharmaceutical, paint, ink and other industries. The most desirable sources of this gum are waste butt logs. Oleoresin from western larch is used to produce turpentine and other products [117].

OTHER MANAGEMENT CONSIDERATIONS:
Pests and Disease: Though many insects and diseases can affect western larch, damage is usually more severe in other associated species [46,131]. Its deciduous habit helps with resistance to pests; if trees are defoliated, they produce a 2nd set of needles later in the season. Repeated defoliation, however, slows growth and may affect competitive ability [12]. Epicormic branching (see General Botanical Characteristics) appears to offer protection against disease by replacing older, potentially infected branches [83].

Dwarf mistletoe (Arceuthobium laricis) is the most serious parasite that affects western larch. Diseases include sporadic needle blight (Hypodermella laricis), needlecast (Meria laricis), and root and stem rots [46,52,116,151].

Larch casebearer (Coleophora laricella) and western spruce budworm (Choristoneura occidentalis) are the most damaging insect pests to western larch. Western spruce budworm affects the form of western larch in western Montana, and height growth may be reduced 25-30% [44]. The most damaging effect of larch casebearer is loss of growth, which may weaken trees, predisposing them to mortality [39,131]. Other insect pests that affect western larch are the larch sawfly (Pristiphora erichsonii) and larch bud moth (Zeiraphera improbana) [46,116]. Species that damage seed cones include the larch cone maggot (Strobilomyia laricis), western spruce budworm larvae, woolly adelgids (Adelges viridis), and cone midges (Resseliella spp.) [121,129].

Some birds and mammals may also affect western larch survival. Birds and rodents may reduce germination capacity by foraging heavily on seeds. Squirrels may damage branches while cutting and caching cones, and bears often completely girdle and kill trees while foraging for sugars [117,131]. A review by Shearer and Kempf [132] reported that up to 5% of pole-size larches have been damaged by bears in a given year at Coram Experimental Forest in Montana.

Stand management: Schmidt and others [117] review literature regarding site preparation, direct seeding, planting, cutting methods, and stand management for western larch. Many western larch stands are susceptible to overstocking when good seed crops, adequate site preparation, and favorable weather coincide. In overstocked stands, individual tree growth may be inhibited, and tree mortality will be high. Dominant trees will eventually emerge, but may be suppressed in height and diameter [115]. In these cases, it may be advantageous to thin stands in order to maintain vigorous, rapidly-growing trees [32]. In western larch stands infested with dwarf mistletoe, Filip and others [47] recommend thinning to increase volume growth and to reduce new infections in remaining trees. Diameter, basal area, height, and cubic-foot volume growth are all improved by thinning of dense western larch stands in the northern Rocky Mountains [112]. Thinning from above may increase mortality from wind throw and exposure [118,119]. Roe and Schmidt [112] describe specific recommendations for thinning western larch.


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