SPECIES: Populus tremuloides
SPECIES: Populus tremuloides
Photo by Charles Webber © California Academy of Sciences
SPECIES: Populus tremuloides
DISTRIBUTION AND OCCURRENCE
GENERAL DISTRIBUTION : Quaking aspen is the most widely distributed tree in North America. It occurs from Newfoundland west to Alaska and south to Virginia, Missouri, Nebraska, and northern Mexico. A few scattered populations occur further south in Mexico to Guanajuato . Quaking aspen is distributed fairly continuously in the East. Distribution is patchy in the West, with trees confined to suitable sites. Density is greatest in Minnesota, Wisconsin, Michigan, Colorado, and Alaska; each of those states contains at least 2 million acres of commercial quaking aspen forest. Maine, Utah, and central Canada also have large acreages of quaking aspen [89,125]. ECOSYSTEMS : FRES10 White-red-jack pine FRES11 Spruce-fir FRES15 Oak-hickory FRES17 Elm-ash-cottonwood FRES18 Maple-beech-birch FRES19 Aspen-birch FRES20 Douglas-fir FRES21 Ponderosa pine FRES22 Western white pine FRES23 Fir-spruce FRES24 Hemlock-Sitka spruce FRES25 Larch FRES26 Lodgepole pine FRES28 Western hardwoods FRES29 Sagebrush FRES34 Chaparral-mountain shrub FRES35 Pinyon-juniper FRES36 Mountain grasslands FRES37 Mountain meadows FRES38 Plains grasslands FRES39 Prairie STATES : AK AZ CA CO CT ID IL IN IA KY MA ME MD MI MN MO MT NE NV NH NJ NM NY ND OH OR PA RI SD TX UT VT VA WA WV WI WY AB BC MB NB NF NT NS ON PE PQ SK YT MEXICO BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 3 Southern Pacific Border 4 Sierra Mountains 5 Columbia Plateau 6 Upper Basin and Range 7 Lower Basin and Range 8 Northern Rocky Mountains 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 14 Great Plains 15 Black Hills Uplift 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : K003 Silver fir-Douglas-fir forest K005 Mixed conifer forest K007 Red fir forest K008 Lodgepole pine-subalpine 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 K016 Eastern ponderosa forest K017 Black Hills pine forest K018 Pine-Douglas-fir forest K019 Arizona pine forest K020 Spruce-fir-Douglas-fir forest K021 Southwestern spruce-fir forest K022 Great Basin pine forest K023 Juniper-pinyon woodland K024 Juniper steppe woodland K029 California mixed evergreen forest K037 Mountain-mahogany-oak scrub K038 Great Basin sagebrush K055 Sagebrush steppe K095 Great Lakes pine forest K096 Northeastern spruce-fir forest K098 Northern floodplain forest K100 Oak-hickory forest K101 Elm-ash forest K106 Northern hardwoods K107 Northern hardwoods-fir forest K108 Northern hardwoods-spruce forest SAF COVER TYPES : 1 Jack pine 5 Balsam fir 12 Black spruce 13 Black spruce-tamarack 15 Red pine 16 Aspen 18 Paper birch 19 Gray birch-red maple 20 White pine-northern red oak-red maple 21 Eastern white pine 25 Sugar maple-beech-yellow birch 26 Sugar maple-basswood 27 Sugar maple 28 Black cherry-maple 30 Red spruce-yellow birch 31 Red spruce-sugar maple-beech 32 Red spruce 33 Red spruce-balsam fir 35 Paper birch-red spruce-balsam fir 37 Northern white-cedar 38 Tamarack 39 Black ash-American elm-red maple 42 Bur oak 51 White pine-chestnut oak 55 Northern red oak 60 Beech-sugar maple 63 Cottonwood 107 White spruce 108 Red maple 201 White spruce 202 White spruce-paper birch 203 Balsam poplar 204 Black spruce 205 Mountain hemlock 206 Engelmann spruce-subalpine fir 207 Red fir 208 Whitebark pine 209 Bristlecone pine 210 Interior Douglas-fir 211 White fir 212 Western larch 213 Grand fir 215 Western white pine 216 Blue spruce 217 Aspen 218 Lodgepole pine 219 Limber pine 220 Rocky Mountain juniper 238 Western juniper 239 Pinyon-juniper 252 Paper birch 256 California mixed subalpine SRM (RANGELAND) COVER TYPES : 105 Antelope bitterbrush-Idaho fescue 107 Western juniper/big sagebrush/bluebunch wheatgrass 318 Bitterbrush-Idaho fescue 401 Basin big sagebrush 402 Mountain big sagebrush 403 Wyoming big sagebrush 411 Aspen woodland 412 Juniper-pinyon woodland 413 Gambel oak 420 Snowbush 421 Chokecherry-serviceberry-rose 422 Riparian 509 Transition between oak-juniper woodland and mahogany-oak association 920 White spruce-paper birch HABITAT TYPES AND PLANT COMMUNITIES : Quaking aspen is a major cover type in North America. In Minnesota, Wisconsin, and Utah, quaking aspen occupies more land than any other forest type. Quaking aspen also occurs in a large number of other forest cover types over its extensive range. It is common in spruce-fir (Picea-Abies spp.) types of the Great Lakes States and central Canada and in mixed northern hardwoods. Mixed jack pine (Pinus banksiana) and quaking aspen occur on the Precambrain shield in Canada and Minnesota. In the Rocky Mountains, quaking aspen groves are scattered throughout Engelmann spruce-subalpine fir (Picea engelmannii-A. lasiocarpa) forests. Quaking aspen is common in mixed conifer forests of New Mexico, Arizona, and California. At its lower altitudinal limit in the western United States, quaking aspen is associated with scrub oaks (Quercus spp.) or sagebrush (Artemisia spp.). Prostrate quaking aspen occur above timberline . Throughout its range, quaking aspen occurs in mid- to upper riparian zones [56,123]. Quaking aspen is listed as a dominant species in over 100 habitat, plant community, and vegetation typings. A comprehensive list of these publications can be obtained by using the Citation Retrieval System (CRS). In CRS, a combination search using the keywords POPTRE and HTS (Populus tremuloides and habitat types), and a second search using the keywords POPTRE and COMM TYPES (P. tremuloides and community types), will produce a list of habitat, plant community, and vegetation typings describing quaking aspen as a dominant species. The search can be narrowed by including the keyword for the state or administrative unit of interest (e.g., search: POPTRE and HTS and CO). Associated shrub species: East - Shrub species commonly associated with quaking aspen in the East include beaked hazel (Corylus cornuta), American hazel (C. americana), mountain maple (Acer spicatum), speckled alder (Alnus rugosa), American green alder (A. viridis spp. crispa), dwarf bush-honeysuckle (Diervilla lonicera), raspberries and blackberries (Rubus spp.), willows (Salix spp.), and gooseberries (Ribes spp.). Great Plains - Additional species occurring with quaking aspen in the prairie provinces included snowberry (Symphoricarpos spp.), highbush cranberry (Viburnum edule), limber honeysuckle (Lonicera dioica), red-osier dogwood (Cornus sericea), western serviceberry (Amelanchier alnifolia), chokecherry (Prunus virginiana), Bebb willow (Salix bebbiana), and roses (Rosa spp.). Alaska - Bebb willow and roses are also associated with quaking aspen in Alaska. Other common shrub associates are Scouler willow (S. scouleriana), bearberry (Arctostaphylos uva-ursi), mountain cranberry (Vaccinium vitis-idaea), and highbush cranberry. Rocky Mountains - Mountain snowberry (Symphoricarpos oreophilus), western serviceberry, chokecherry, common juniper (Juniperus communis), Oregon-grape (Berberis repens), Wood's rose (R. woodsii), myrtle pachistima (Pachistima myrsinites), redberry elder (Sambucus pubens), and a number of Ribes species are associated with quaking aspen in the Rocky Mountains . Pacific Northwest - In valleys west of the Cascades in Oregon and Washington, quaking aspen alternates dominance with Douglas hawthorn (Crataegus douglasii). Quaking aspen grows through the Douglas hawthorn overstory, resulting in reduced vigor of Douglas hawthorn. Quaking aspen eventually dies back, releasing Douglas hawthorn in the understory . Associated herbaceous species: East - Herbs commonly found in the understory of quaking aspen in the East include largeleaf aster (Aster macrophyllus), wild sarsaparilla (Aralia nudicaulis), Canada beadruby (Maianthemum canadense), bunchberry (Cornus canadensis), yellow beadlily (Clintonia borealis), roughleaf ricegrass (Oryzopsis asperifolia), sweet-scented bedstraw (Galium triflorum), sweetfern (Comptonia perigrina), lady fern (Athyrium filix-femina), bracken fern (Pteridium aquilinum), sedges (Carex spp.), and goldenrods (Solidago spp.). West - The herbaceous component of quaking aspen communities in the West is too diverse to list. Forbs dominate most sites .
SPECIES: Populus tremuloides
WOOD PRODUCTS VALUE : Quaking aspen is one of the most important timber trees in the East. Its wood is used primarily for particleboard, especially waferboard and oriented strandboard, and for pulp. In the Great Lakes States, quaking aspen is the preferred species for making oriented strandboard. Quaking aspen fibers are well suited for making fine paper. Some quaking aspen is used for lumber. Quaking aspen lumber is used for making boxes, crates, pallets, and furniture. A small but growing volume is made into studs. Quaking aspen wood is little used in the West, except in Colorado, where it is used for pulp and particleboard . Specialty products from quaking aspen wood include excelsior, matchsticks, and tongue depressors. Quaking aspen pellets are used for fuel [125,170]. The wood of quaking aspen is light, soft, and straight grained. It has good dimensional stability and it turns, sands, and holds glue and paint well. It has relatively low strength, however, and is moderately low in shock resistance. Both sapwood and heartwood have low decay resistance and are difficult for preservatives to penetrate [125,170]. Quaking aspen wood warps with conventional processing, but saw-dry-rip processing controls warping . IMPORTANCE TO LIVESTOCK AND WILDLIFE : Quaking aspen forests provide important breeding, foraging, and resting habitat for a variety of birds and mammals. Wildlife and livestock utilization of quaking aspen communities varies with species composition of the understory and relative age of the quaking aspen stand. Young stands generally provide the most browse. Quaking aspen crowns can grow out of reach of large ungulates in 6 to 8 years . Although many animals browse quaking aspen year-round, it is especially valuable during fall and winter, when protein levels are high relative to other browse species . Large wild ungulates: Elk browse quaking aspen year-round in much of the West, feeding on bark, branch apices, and sprouts [38,42,102]. In some areas, elk use it mainly in winter . In northwestern Wyoming, elk begin browsing quaking aspen as soon as they move onto winter ranges in November and continue to use it through March . Quaking aspen is important forage for mule and white-tailed deer. Deer consume the leaves, buds, twigs, bark, and sprouts [42,102,158]. New growth on burns or clearcuts is especially palatable to deer [42,43]. Deer in many areas use quaking aspen year-round , although in some western states, deer winter below the aspen zone [42,43]. Quaking aspen communities are described as the major "deer-producing forest type" in the north-central United States . In the Great Lakes States, quaking aspen is primary browse for white-tailed deer and moose . Stands less than 30 years of age provide optimum forage for deer in Minnesota . In some locations, sprouts provide key summer forage for deer after herbaceous species have cured [42,43]. Quaking aspen is one of the most important items in the summer diet of mule deer on the Kaibab National Forest of Arizona [159,161], and comprises up to 27 percent of the summer diet of mule deer in parts of central Utah . However, it is relatively unimportant deer browse in parts of South Dakota . Mule deer in Utah have been observed consuming large amounts of quaking aspen leaves after autumn leaf fall [42,161]. Quaking aspen is valuable moose browse for much of the year . Moose utilize it on summer  and winter ranges [23,42,135]. Quaking aspen, paper birch (Betula papyrifera), and willows (Salix spp.) make up more than 95 percent of the winter hardwood browse utilized by moose on Alaska's Kenai Peninsula . Relatively high levels of moose use have been reported from early summer through late fall in Minnesota  and Idaho . Young stands generally provide the best quality moose browse . However, researchers in Idaho found that in winter, moose browsed mature stands of quaking aspen more heavily than nearby clearcuts dominated by quaking aspen sprouts . Bison once favored quaking aspen-grassland transition zones in Manitoba and Saskatchewan [32,102]. However, little is known about the historic importance of quaking aspen browse to bison. Meagher  found that woody plants made up only 1 percent of the diet of bison in Yellowstone National Park, and she did not list quaking aspen as one of the woody species bison used. Bears: Black and grizzly bears feed on forbs and berry-producing shrubs in quaking aspen understories. Quaking aspen forests in Alberta provide excellent denning and foraging sites for black bear . Lagomorphs: Rabbits and hares feed on quaking aspen in summer and winter [42,43]. In winter, snowshoe hare and cottontail rabbits eat quaking aspen buds, twigs, and bark [42,43]. Quaking aspen is one of the most important and nutritious summer browse species for rabbits in Alberta , and is a preferred winter food of snowshoe hare in Manitoba . Pikas also feed on quaking aspen buds, twigs, and bark . Lagomorphs may girdle suckers or even mature trees [23,102]. In some parts of Canada, fairly high quaking aspen mortality has been attributed to rabbits and hares [20,102]. Rodents and shrews: Small rodents such as squirrels, pocket gophers, mice, and voles feed on quaking aspen during at least part of the year [43,88,158]. Mice and voles frequently consume quaking aspen bark below snow level, and can girdle suckers and small trees [23,43,88,152]. The southern red-backed vole, deer mouse, and white-footed mouse are dominant small mammals in quaking aspen communities of northern Minnesota and upper Michigan. Small mammal populations in quaking aspen generally fluctuate widely with stand age and annual variation in animal population size. Highest densities typically occur in mature quaking aspen stands. Field mice (Peromyscus spp.), for example, are most abundant in mature quaking aspen communities . The red-backed vole, however, is most abundant in sapling stands, somewhat less abundant in mature stands, and least common in clearcuts. Quaking aspen provides food for porcupine in winter and spring [23,42,43]. In winter, porcupine eat the smooth outer bark of the upper trunk and branches. Porcupine girdling of quaking aspen has killed large tracts of merchantable trees in Minnesota. In spring, porcupine eat quaking aspen buds and twigs . Beaver consume the leaves, bark, twigs, and all diameters of quaking aspen branches . They use quaking aspen stems for constructing dams and lodges [42,102]. At least temporarily, beaver can eliminate quaking aspen from as far as 400 feet (122 m) from waterways [6,23]. An individual beaver consumes 2 to 4 pounds (1-2 kg) of quaking aspen bark daily, and it is estimated that as many as 200 quaking aspen stems are required to support one beaver for a 1-year period [42,43]. Birds: Quaking aspen communities provide important feeding and nesting sites for a diverse array of birds . Bird species using quaking aspen habitat include sandhill crane, western wood pewee, six species of ducks, blue, ruffed, and sharp-tailed grouse, band-tailed pigeon, mourning dove, wild turkey, red-breasted nuthatch, and pine siskin. Quaking aspen is host to a variety of insects that are food for woodpeckers and sapsuckers . Generally, moist to mesic quaking aspen sites have greater avian species diversity than quaking aspen stands on dry sites [40,42]. Many bird species utilize quaking aspen communities of only a particular seral stage. Research at a northern Utah site suggests that blue grouse, yellow-rumped warbler, warbling vireo, dark-eyed junco, house wren, and hermit thrush prefer mature quaking aspen stands. The MacGillivray's warbler, chipping and song sparrows, and lazuli bunting occur in younger stands [39,42]. Bluebirds, tree swallow, pine siskin, yellow-bellied sapsucker, and black-headed grosbeak favor quaking aspen community edges . Ruffed grouse: Through most of its range, ruffed grouse depends on quaking aspen for foraging, courting, breeding, and nesting sites [23,42,70]. It uses quaking aspen communities of all ages. Favorable ruffed grouse habitat includes quaking aspen stands of at least three different size classes [23,70]. Young (2- to 10-year-old) stands provide important brood habitat, and 10- to 25-year-old stands are favored overwintering and breeding areas . Quaking aspen leaves and buds are readily available in abundant quantities in stands greater than 25 years of age, and such older stands are used for foraging [70,122]. Ruffed grouse chicks find protection in dense, young aspen suckers as early as 1 year after fire or other disturbance . Pole-size stands appear to offer the best breeding habitat and may support one breeding bird per 3 to 4 acres (1.2-1.6 ha). Breeding generally does not occur in stands exceeding 25 years of age or with a density less than approximately 2,000 stems per acre . Quaking aspen buds, catkins, and leaves provide an abundant and nutritious, year-long food source for ruffed grouse [23,70]. Vegetative and flower buds are the primary winter and spring foods of the ruffed grouse. Ruffed grouse eat 6 times more quaking aspen buds than buds from all other species combined . It is estimated that ruffed grouse can consume more than 45 quaking aspen buds per minute and can satisfy their daily winter food needs in as little as 15 to 20 minutes . Ruffed grouse generally begin feeding on staminate flower buds from several weeks prior to the period of snow accumulation, and continue well into early spring [23,70]. Male ruffed grouse feed on staminate catkins until at least early May . Nesting hens consume large quantities of new quaking aspen leaves early in the spring [23,70]. Ruffed grouse consume quaking aspen leaves throughout the summer , and the leaves are considered to be the second most important food source during the fall. Ruffed grouse appear to prefer certain clones. Buds from some clones may be up to 30 percent richer in protein than buds from neighboring clones . Livestock: Most classes of domestic livestock use quaking aspen. Domestic sheep and cattle browse the leaves and twigs [158,161]. Domestic sheep browse quaking aspen more heavily than cattle [158,161]. It is estimated that domestic sheep consume 4 times more quaking aspen sprouts than cattle. Heavy livestock browsing can adversely impact quaking aspen growth and regeneration [42,43,161]. PALATABILITY : Quaking aspen is palatable to all browsing livestock and wildlife species [38,23,42,84,161,169]. The buds, flowers, and seeds are palatable to many bird species including numerous songbirds and ruffed and sharp-tailed grouse [42,168]. Palatability of quaking aspen for livestock and wildlife species has been rated as follows : CO MT ND OR UT WY Cattle Fair Fair Fair ---- Fair Fair Domestic sheep Fair Good Good ---- Fair Good Horses Fair Fair Fair ---- Fair Fair Pronghorn ---- ---- Poor ---- Fair Fair Elk Good Fair ---- ---- Good Good Mule deer Good Fair Fair ---- Good Good White-tailed deer Good Fair Fair ---- ---- Good Small mammals ---- Fair ---- ---- Fair Good Small nongame birds ---- Fair Fair ---- Fair Fair Upland game birds ---- Good Good ---- Fair Good Waterfowl ---- ---- ---- ---- Poor Poor NUTRITIONAL VALUE : Overall energy and protein values of quaking aspen are rated "fair" . Nutritional content of quaking aspen browse varies seasonally, by plant part, and by clone [11,40,159]. Protein content drops as the growing season progresses [42,179]. On a Utah site, average leaf protein dropped from 17 percent in early June to 3 percent at abscission. Clonal variation in leaf protein ranged from 13.4 to 20.9 percent in June and from 10.1 to 14.6 percent in September. Average twig protein dropped from 17 percent in spring to 6 to 7 percent in winter. Twig nitrogen, phosphorus, and potassium levels dropped from spring to winter, but twig calcium, magnesium, sodium, and fat levels increased. Phosphorus values in September averaged only 58 percent of those in June . Mean composition of quaking aspen terminal shoots, collected in March and April in Soldotna, Alaska, was as follows : dry matter (%) 43.6 gross energy (kcal/g) 5.1 crude protein (%) 7.9 neutral-detergent fiber (%) 54.9 acid-detergent fiber (%) 40.1 lignin (%) 10.5 ash (%) 1.9 in-vitro digestibility for moose (%) 42.0 COVER VALUE : Wild and domestic ungulates use quaking aspen for summer shade, and quaking aspen provides some thermal cover for ungulates in winter [42,35,152]. Seral quaking aspen communities provide excellent hiding cover for moose, elk, and deer [42,161]. Deer use quaking aspen stands for fawning grounds in the West . Ungulates generally do not use quaking aspen much in winter. Perala  reported that in the Great Lake States, pure quaking aspen stands provided white-tailed deer with relatively poor insulation and protection from winter winds compared to adjacent stands of conifers. Quaking aspen provides good hiding and thermal cover for many small mammals . Snowshoe hare use it for hiding and resting cover in summer [42,43]. Beaver use quaking aspen branches for dams and lodges. A variety of bird species use quaking aspen for hiding, nesting, and roosting cover . Sapling and pole-size stands provide especially good winter cover for birds . Snow tends to accumulate earlier and deeper in quaking aspen than in adjacent conifer stands, and ruffed grouse use the deep snow for burrowing cover in winter . Dense stands of fairly small diameter stems (<6 inches [15cm]) provide the best protection from predators. Overall cover value for ruffed grouse is enhanced in stands containing several size classes . Over 4 years, 22 to 65 pairs of breeding birds were found in 10 acres (4 ha) of quaking aspen in northern Utah. Species nesting in quaking aspen included the broad-tailed hummingbird, northern flicker, house wren, American robin, warbling vireo, yellow-rumped warbler, junco, western wood pewee, and lazuli bunting . The following other species also nest in mature quaking aspen communities : canopy nesters - pewees, vireos, western tanager, Cassin's finch, least flycatcher ground nesters - hermit thrush, Townsend`s solitaire, dark-eyed junco, white-crowned and Lincoln`s sparrows, veery, ovenbird, nighthawk, Connecticut and mourning warblers shrub nesters - flycatchers (Empidonax spp.), rose-breasted and black-headed grosbeaks, chipping, clay-colored, and song sparrows, yellow and MacGillivray`s warblers, rufous-sided and green-sided towhees, black-billed cuckoo cavity nesters - chickadees, nuthatches, woodpeckers, owls, sapsuckers, hairy and downy woodpeckers General cover value of quaking aspen has been rated as follows : CO MT ND OR UT WY Pronghorn ---- ---- Poor ---- Poor Poor Elk Fair Good ---- ---- Good Good Mule deer Fair Good Poor ---- Good Good White-tailed deer Fair Good Fair ---- ---- Good Small mammals ---- Good ---- ---- Good Good Small nongame birds Good Good Good ---- Good Good Upland game birds Poor Good Good ---- Good Good Waterfowl ---- ---- ---- ---- Poor Poor VALUE FOR REHABILITATION OF DISTURBED SITES : Aspens (Trepidae) are unique in their ability to stabilize soil and watersheds. Fire-killed stands are promptly revegetated by root sprouts (suckers). The trees produce abundant litter that contains more nitrogen, phosphorus, potash, and calcium than leaf litter of most other hardwoods. The litter decays rapidly, forming a nutrient-rich humus that may amount to 25 tons per acre (oven-dry basis). The humus reduces runoff and aids in percolation and recharge of ground water. Litter and humus layers reduce evaporation from the soil surface. Compared to conifers, more snow accumulates under quaking aspen and snowmelt begins earlier in the spring. Soil under quaking aspen thaws faster and infiltrates snow more rapidly than soil under conifers . Wide adaptability of quaking aspen makes it well-suited for restoration and rehabilitation projects on a wide range of sites. Seedlings transplanted onto disturbed sites have shown good establishment . Seedlings have some advantages over vegetative cuttings. In large-scale greenhouse production, quaking aspen seedlings are more economical to establish and grow . Seedlings grow a taproot and secondary roots quickly, while quaking aspen cuttings can be slow to establish an adequate root system . Also, genetic diversity is greater among seedlings than cuttings . Seed stored at 4 degrees Fahrenheit (-20 deg C) has retained viability for at least 2 years. Fung and Hamel  and Schier and others  provide procedures for collecting and processing quaking aspen seed. The major advantage of using quaking aspen cuttings is that clones with desirable traits can be selected as parent stock. Quaking aspen vegetative cuttings are difficult to root, however [123,146]. Stem cuttings are especially difficult to root unless taken from young sprouts. Root cuttings taken from young sprouts are generally most successful. Schier and others  provide information on growing quaking aspen cuttings in the greenhouse. Case examples - Riparian: In riparian and lodgepole pine (Pinus contorta) zones of Lost Canyon near Fresno, California, restoration was needed after a hydroelectric plant pipe broke, scouring part of the canyon. Quaking aspen seedlings showed 99.2 percent survival (or 357 live seedlings) and had a mean height of 10.6 inches (26.6 cm) 1 year after transplant . Strip-mined sites: Some old strip-mined sites in Pennsylvania, Ontario, and elsewhere have not revegetated due to extreme acidity of the soil. Quaking aspen is one of the first native tree species to volunteer on these soils after application of lime [81,168]. Mine spoils: Quaking aspen transplants were successfully established on phosphate mine spoils in southeastern Idaho that received only 18 inches (450 mm) of annual precipitation . OTHER USES AND VALUES : Mountain slopes covered by quaking aspen provide high yields of good-quality water. Quaking aspen intercepts less snow than conifers, so snowpack is often greater under quaking aspen . Well-stocked quaking aspen stands provide excellent watershed protection. The trees, the shrub and herbaceous understories, and the litter of quaking aspen stands provide nearly 100 percent soil cover. Soil cover and the intermixture of herbaceous and woody roots protect soil except during very intense rains . Quaking aspen is valued for its aesthetic qualities at all times of the year. The yellow, orange, and red foliage of autumn particularly enhances recreational value of quaking aspen sites . Quaking aspen is widely used in ornamental landscaping . OTHER MANAGEMENT CONSIDERATIONS : It is somewhat unclear why some quaking aspen stands break up and die while others remain stable. The age at which quaking aspen clones begin to die probably has a genetic component. Site quality can also be a major factor . Is it well documented in the Great Lakes States that environmental variables affect quaking aspen longevity [63,93]. Stands in this region may deteriorate* rapidly; more than half the trees in a well-stocked stand may die in 6 years . In Utah, however, clone deterioration was found to occur over a number of generations of sprouts . Schier and Campbell  found that on the Wasatch National Forest near Logan, Utah, concentrations of phosphorus and percent silt were significantly lower on soils with deteriorating clones than on soils with healthy clones. Ten deteriorating clones and ten healthy clones were studied. *Deteriorating stands are defined as those stands with a low density of stems that are younger and smaller in size, and with poorer form and higher crown:stem ratios, than healthy stands . Cryer and Murray  speculated that both soil type and disturbance are important in quaking aspen stability. As a quaking aspen stand matures, a humus-rich (mollic) soil layer develops. Quaking aspen thrive for a time, but without disturbance gradually begin to age and deteriorate. With deterioration, the soil loses organic matter and thickness. With loss of humus and litter, rapid percolation leaches the soil, which becomes thinner, more acidic, and lower in nutrients. Acidic, low-nutrient soils support conifers more readily than quaking aspen. Disturbances such as burning or clearcutting tend to maintain quaking aspen. If soil is already thin and acidic, however, clearcutting will probably convert the site to conifers. Quaking aspen on such sites has been observed to sprout, grow to about 3 feet (0.9 m) in height, and begin to die. A deteriorating stand that is burned may be more likely to revert to quaking aspen because burning increases soil pH and adds organic carbon and nutrients to the soil. However, fire will probably not rejuvenate the stand if quaking aspen biomass is so low that burning does not appreciably raise soil pH and nutrient levels. Sucker vigor will probably be low. Range: There is increasing concern that in the West, poor quaking aspen regeneration is due, at least in part, to wildlife overbrowsing young sprouts . Where browsing pressure is heavy, ungulates may remove quaking aspen regeneration before it grows above browseline. To provide for quaking aspen regeneration in such areas, enough quaking aspen must be removed to create an unbrowsed surplus of new growth . A few areas of the West have such large elk populations that even after large-scale wildfires, quaking aspen sprouts attained little height growth because of intense browsing. In such areas, quaking aspen sprouts probably require protection from browsing . Promoting quaking aspen: Prescribed burning is one method of promoting quaking aspen (see FIRE MANAGEMENT). When prescribed burning is not desired or feasible, clearcutting or bulldozing is recommended [77,177]. Clearcutting often results in a sucker stand of 50,000 to 100,000 stems per hectare [17,35,49]. A basal area of less than 4 trees/sq m/ha is recommended to promote sprouting [87,122]. Partial cuttings seriously inhibit sprouting because apical dominance is retained in standing stems, and shade from standing stems reduces vigor of the few suckers that do appear . Clearcutting in southeastern boreal forest: Lavertu and others  found that in balsam fir-northern white-cedar (Abies balsamea-Thuja occidentalis) forest in Quebec, quaking aspen showed strong sprouting response regardless of forest seral stage, number of quaking aspen present before cutting, quaking aspen stem age, or quaking aspen root density. After clearcutting on sites that had burned 46, 74, 143, 167, and 230 years earlier, quaking aspen sprouted vigorously even on the site that had not burned for 230 years, had only a single, living quaking aspen stem, and the lowest quaking aspen root density of all five site types. Initial sprouting densities were greater in younger stands, but due to greater mortality of sprouts in younger stands, differences in sprouting density between different-aged stands were not significant 3 years after clearcutting. Bulldozing: Carefully done, whole-tree bulldozing can stimulate quaking aspen suckering [177,178]. Operations that cause deep cutting or compaction of soil will reduce sprouting . Shepperd  obtained good quaking aspen regeneration by pushing over whole trees using a rubber-tire skidder with the blade positioned above ground level. This technique severed large roots to a distance of 3.3 to 5 feet (1-1.5 m) from the stem. Five years after treatment, quaking aspen suckers averaged 37,888 per hectare when slash was removed and 10,131 per hectare with slash intact. In contrast, sites that were clearcut averaged 17,544 stems per hectare (no slash) and 7,038 stems per hectare (slash) . Quaking aspen control: On some sites, it may be desirable to convert quaking aspen to another vegetation type. Stand conversion may be relatively easy on dry or poorly drained sites, or on sites were quaking aspen is exposed to snow damage. Quaking aspen production is usually low on such sites to begin with, and such stands are prone to breakup. On other sites, it may not be possible to eliminate quaking aspen, but quaking aspen can probably be reduced . Very small clearcuts reduce quaking aspen abundance because sprouting response is weak after such treatment . Girdling also reduces abundance; sprouting occurs after girdling, but shade provided by standing dead stems increases sprout mortality. Also, it is thought that girdling promotes decay of the root system . Use of glyphosate after cutting has been shown to control quaking aspen regeneration for some time [122,123]. In Quebec, quaking aspen in a quaking aspen-paper birch stand originating after a 1944 fire was partially controlled by removing overtopping quaking aspen when the stand was 7 and 14 years of age. Stocking varied as follows at postfire year 34 . _______________________________________________________________________________ Treatment | Stocking ______________________________|________________________________________________ control (no treatment) | 5% paper birch; 90% aspen; 5% mixed hardwoods Aug. 1951 cut & Nov. 1958 cut | 90% paper birch; 10% aspen Nov. 1951 cut & Nov. 1958 cut | 44% paper birch; 41% aspen; 15% mixed hardwoods Nov. 1951 cut & May 1959 | herbicide (injection in | 32% paper birch; 63% aspen; 5% mixed hardwoods ____aspen only)_______________|________________________________________________
SPECIES: Populus tremuloides
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS : Quaking aspen is a native deciduous tree. It is small- to medium-sized, typically less than 48 feet (15 m) in height and 16 inches (40 cm) dbh . It has spreading branches and a pyramidal or rounded crown [60,75,88,166]. The bark is thin. Leaves are orb- to ovately shaped, with flattened petioles . The fruit is a tufted capsule bearing six to eight seeds. A single female catkin usually bears 70 to 100 capsules [88,166]. The root system is relatively shallow, with widespreading lateral roots and vertical sinker roots descending from the laterals. Laterals may extend over 100 feet (30 m) into open areas . Gifford  found that vertical roots of quaking aspen in Utah extended more than 9 feet (2.7 m) down, branching into fine, dense roots at their extremities . Quaking aspen forms clones connected by a common parent root system. It is typically dioecious, with a given clone being either male or female. Some clones produce both stamens and pistils, however . Quaking aspen stands may consist of a single clone or aggregates of clones . Clones can be distinguished by differences in phenology, leaf size and shape, branching habit, bark character, and by electrophoresis . In the West, quaking aspen stands are often even-aged, originating after a single top-killing event. Some stands, resulting from sprouting of a gradually deteriorating stand, may be only broadly even-aged . Clones east of the Rocky Mountains tend to encompass a few acres at most , and aboveground stems are short lived. Maximum age of stems in the Great Lakes States is 50 to 60 years. Clones in the West tend to occupy more area, and aboveground stems may live up to 150 years . A male clone in the Wasatch Mountains of Utah occupies 17.2 acres (43 ha) and has more than 47,000 stems. To date, it is the world's most massive known organism. Clone age can be great; the large Utah clone is estimated to be 1 million years old . Seedling morphology: Quaking aspen seedlings can easily be misidentified as cottonwood (Populus spp.) or willow (Salix spp.) seedlings because quaking aspen seedlings bear only a slight resemblance to the adult form. Leaves of quaking aspen seedlings are nearly lanceolate. During the first growing season, vertical flattening of the leaf petioles is not obvious, and there is no lateral branching. By the second growing season, leaves are characteristically orbicular to ovate, and there is vertical branching. Renkin and others  have published photographs of excavated quaking aspen seedlings. Quaking aspen seedlings can be differentiated from root sprouts by leaf morphology, lack of woody tissue, lack of vertical shoots, and presence of a taproot [90,133]. There are a few visual clues that can distinguish seedlings from sprouts without excavation. Seedlings have paired cotyledons or cotyledon scars a few millimeters above the soil surface. The first pair of true leaves is nearly opposite, at right angles to, and directly above the cotyledons. Leaf pattern of sprouts is strongly alternate . Physiology: Quaking aspen is not shade tolerant [123,130]; neither does it tolerate long-term flooding nor waterlogged soils . Even if quaking aspen survives flooding in the short term, stems subjected to prolonged flooding usually develop a fungus infection that greatly reduces stem life (and renders the wood commercially useless) [37,118,126]. Sprouting is hormonally controlled in quaking aspen. Sprouting is suppressed by auxin, which is transported from the stem to the roots. Auxin therefore maintains apical dominance. When stems are killed and apical dominance is removed, cytokinins in the roots initiate root sprouting. Clones with a strong tendency to sprout probably have high cytokinin:auxin ratios . RAUNKIAER LIFE FORM : Phanerophyte Geophyte REGENERATION PROCESSES : Quaking aspen regenerates from seed and by sprouting from the roots . Stump and root crown sprouting is rare in older trees, but saplings sometimes sprout from the stump and root crown as well as the roots [123,145]. Vegetative reproduction: Root sprouting is the most common method of regeneration. Root suckers originate from meristems in the root's cork cambium and can develop anytime during secondary growth . Saplings may begin producing root sprouts at 1 year of age . There are thousands of suppressed shoot primoridia on the roots of most mature quaking aspen clones. Recently initiated meristems or primordia usually sprout and elongate more vigorously than older primorida or suppressed root buds . Root suckering is affected by depth and diameter of parent roots. In Utah and Wyoming, Schier and Campbell  found that 25 percent of sprouts came from roots within 1.6 inches (4 cm) of the surface, 70 percent from within 3.2 inches (8 cm), and 92 percent within 4.7 inches (28 cm). Compared with parent roots of quaking aspen in the Great Lakes States, those of quaking aspen in the West were deeper. On a Utah burn site, high-severity fires increased the depth of the parent roots from which sprouts originated. Range in diameter of roots producing sprouts was 0.04 to 3.7 inches (0.1-9 cm). Sixty percent of suckers grew from roots smaller than 0.4 inch (1 cm) in diameter, 88 percent from roots smaller than 0.8 inch (2 cm), and 93 percent from roots smaller than 1.2 inches (3 cm) in diameter. On a Wyoming site, the percentages were 38 percent, 68 percent, and 86 percent, respectively. Sprout development is largely suppressed by apical dominance . Closed stands produce a few inconspicuous sprouts each growing season; the sprouts usually die unless they occur in a canopy gap. When stems are removed by cutting, burning, girdling, or defoliation, suppressed primoridia, buds, and shoots resume growth. Best sucker production follows either a fire that kills all parent trees and brush or other complete clearing . The number of suckers produced can vary markedly among clones [7,159], but the potential for suckering is enormous. Jones  indicated that 20,000 to 30,000 sprouts per acre is typical the first year following top-kill. Natural thinning is heavy and effective. The least vigorous suckers die within 1 to 2 years. After 5 to 10 years, most sucker clumps reduce to a single stem . Most stems are overtopped by more vigorous neighbors. Diseases, insects, browsing mammals, and snow damage also reduce sprout density [35,87,108]. Bella and De Franceschi  reported that in Alberta and Saskatchewan, stem density averaged 280,000 per hectare at age 2; 190,000 per hectare at age 3; and 80,000 per hectare at age 5. Seedling establishment: Quaking aspen commonly establishes from seed in Alaska, northern Canada, and eastern North America. Seedling establishment is less common in the West, where rainfall is often followed by dry periods that kill newly germinated seedlings . Even in the West, however, quaking aspen may establish from seed more frequently than previously thought. Studies on frequency of seedling establishment in the West are conflicting. Some researchers found absolutely no quaking aspen seedling establishment despite diligent searching [4,5,16]; others reported the presence of only one  or a few  seedlings, while still other researchers documented the presence of hundreds of seedlings [7,90,97,167]. Only since the stand-replacement fires of the late 1980's have researchers used permanent plots to monitor quaking aspen seedling establishment and survival in the West. Data from one such study are summarized after the following discussion of sexual reproduction in quaking aspen. Sexual reproduction: The staminate-pistillate ratio of adult clones is 1:1 in most localities, although it may be as high as 3:1 or more . Some clones alternate between staminate and pistillate forms in different years, or produce various combinations of perfect, staminate, and pistillate flowers . Quaking aspen first flowers at 2 to 3 years. Minimum tree age for production of large seed crops is 10 to 20 years, and maximum seed production occurs at about 50 years of age. In Utah, one 23-year-old tree produced an estimated 1.6 million seeds in one spring . There are 3- to 5-year intervals between heavy seed crops [55,102,110,148]. Seeds disperse a few days after they ripen. Dispersal lasts 2 to 3 weeks . The plumose seeds are dispersed by wind for distances of 1,600 feet (500 m) to several miles with heavy winds. Seeds also disperse by water, and can germinate while floating or submerged . Viability of fresh seed is good; germination of 80 to 95 percent is reported under laboratory conditions [103,109,142]. Viability lasts 2 to 4 weeks under favorable conditions of low temperature and humidity , but seed loses viability rapidly under less than optimum conditions [54,171]. Optimum conditions for germination and seedling survival include a moist mineral seedbed with adequate drainage, moderate temperature, and freedom from competition . In various collections, seeds have germinated at temperatures from 32 to 102 degrees Fahrenheit (0-39 deg C), with germination sharply reduced from 35 to 41 degrees Fahrenheit (2-5 deg C) and progressively curtailed above 77 degrees Fahrenheit (25 deg C) [54,172]. Quaking aspen seed from northern Utah showed optimal germination between 59 and 68 degrees Fahrenheit (15-20 deg C), and had no light requirement. Seeds germinated best on the soil surface, with emergence decreased by shallow burial . Burned or scarified soil is an excellent seedbed ; litter provides the poorest seedbed. The primary root grows slowly the first few days following germination, and during this critical period the seedling depends upon a brush of hairs to absorb water and anchor the plant . Minor disturbances can uproot surface-germinated seedlings, and a drying seedbed can rapidly desiccate seedlings . Seedlings may reach 6 to 24 inches (15-61 cm) in height by the end of their first year, and roots may extend 6 to 10 inches (15-25 cm) in depth and up to 16 inches (41 cm) laterally. Roots grow more rapidly than shoots; some seedlings show little top-growth until about their third year . During the first several years, natural seedlings grow faster than planted seedlings but not as fast as sprouts. High mortality characterizes young quaking aspen stands regardless of origin. In both seedling and sprout stands natural thinning is rapid. Stems that occur below a canopy die within a few years . Seedling study: Kay  documented postfire quaking aspen seedling establishment following 1986 and 1988 fires in Grand Teton and Yellowstone National Parks, respectively. He found seedlings were concentrated in kettles and other topographic depressions, seeps, springs, lake margins, and burnt-out riparian zones. A few seedlings were widely scattered throughout the burns. In Grand Teton National Park, establishment was greatest (950-2,700 seedlings/ha) in 1989, a wet year, but hundreds to thousands of seedlings established each year despite drought conditions in 1986-1988 and 1990-1991. Seedlings surviving past one season occurred almost exclusively on severely burned surfaces. In Grand Teton National Park, where seedlings were monitored for several years, surviving seedlings were associated with bare mineral soil, ash, and the absence of competing vegetation. In both Parks, 100 percent of seedlings were browsed, and mean heights of seedlings at postfire year 5 (Grand Teton) and postfire year 3 (Yellowstone) were nearly equal to mean heights at postfire year 1. During the same period, 0 percent of lodgepole pine seedlings were browsed. Kay predicted that long-term survival of quaking aspen seedlings will be low. Most seedlings established on depressions that are subject to spring flooding. Since quaking aspen does not tolerate standing water, seedlings on depressions such as kettles and lake margins will probably die in the first prolonged flood. At postfire year 5, quaking aspen seedlings in Grand Teton National Park attained only 5 percent more height growth than attained in the first postfire year. In contrast, lodgepole pine seedlings had increased in height by an average of 176 percent. SITE CHARACTERISTICS : Quaking aspen occurs on a wide variety of sites [40,111]. It grows on moist upland woods, dry mountainsides, high plateaus, mesas, avalanche chutes, talus, parklands, gentle slopes near valley bottoms, alluvial terraces, and along watercourses [40,109,158,166]. Climate: Climatic conditions vary widely over the range of quaking aspen, especially minimum winter temperatures and annual precipitation. Generally, quaking aspen occurs where annual precipitation exceeds evapotranspiration. In Alaska and northwestern Canada, quaking aspen is common in the boreal zone and extends into the warmest, frost-free sites of the permafrost zone. At the eastern edge of quaking aspen's range, climate is humid, with snowfall exceeding 120 inches (3,050 mm) per year. The southern limit of quaking aspen distribution in the East is roughly delineated by the 75 degree Fahrenheit (24 deg C) mean July temperature isotherm. In the central Rocky Mountains, altitude plays an important role in quaking aspen distribution. The lower limit of its range coincides with a mean annual temperature of 45 degrees Fahrenheit (7 deg C) . Soils: Quaking aspen grows on soils ranging from shallow and rocky to deep loamy sands and heavy clays. Good quaking aspen sites are usually well drained, loamy, and high in organic matter and nutrients . Cryer and Murray  stated that stable quaking aspen stands are found on only one soil order - mollisols - and a few soil subgroups of which Agric Pachic Cryoborolls and Pachic Cryoborolls are dominant. The best stands in the Rocky Mountains and Great Basin are on soils derived from basic igneous rock such as basalt, and from neutral or calcareous shales and limestones. The poorest stands are on soils derived from granite. In the Great Lakes States, the best stands occur in lime-rich, gray glacial drift . Elevation: Quaking aspen spans an elevational range from sea level on both coasts to 11,500 feet (3,505 m) in northern Colorado. At its northern limit, quaking aspen is found only up to 3,000 feet (910 m). In Baja California, it does not occur below 8,000 feet (2,440 m). In Arizona and New Mexico is is most abundant between 6,500 and 10,000 feet (1,980-3,050 m); in Colorado and Utah, it occurs about 1,000 feet (300 m) higher. At either of its elevational limits, quaking aspen is stunted. At its lower limit, it grows as a scrubby tree along streambanks; at high elevations, its stems are bent or prostrate . Aspect: In Alaska and western Canada, quaking aspen grows best on south to southwesterly exposures. It is common on all aspects in the West, except in the Southwest, where it is most common on northern aspects. In the prairie provinces of Canada, particularly on the prairie-woodland interface, quaking aspen occurs on cooler north and east slopes, and in depressions . SUCCESSIONAL STATUS : Quaking aspen is shade intolerant and cannot reproduce beneath its own canopy [23,40,98,123,126]. Beyond that, there is no single, generalized pattern of succession in quaking aspen. Quaking aspen is seral to conifers in most of its range in the West, and in some portions of its eastern range. In the East, quaking aspen is also replaced by hardwoods [23,98]. In the Great Lakes States, successional trends are toward northern hardwoods, spruce-fir, ash-elm (Fraxinus-Ulmus spp.), oak (Quercus spp.), swamp conifers, and pine (Pinus spp.) types, in decreasing order of importance . Where it is seral, quaking aspen usually persists as a minor tree in late seral stages . The canopy closes rapidly in young aspen stands . A quaking aspen stand in Ontario closed and reached maximum development (foliage/unit area of soil surface) in 4 years [127,128]. If quaking aspen does not remain stable, rate of succession to other species varies with with soil, site, and invading species . Mueggler  stated that succession to conifers may occur in a single generation, or take longer than 1,000 years. Harper  found that in central Utah, quaking aspen succeeded to conifers in 75 to 100 years on sandstone soils. On limestone or alluvial soils, succession to conifers took 140 years or more. Quaking aspen is apparently stable on some sites. On some former pine stands in the East, extensive clearcutting of the conifer overstory has removed the pine seed sources. Quaking aspen has formed an apparently stable overstory on many of these sites . Quaking aspen stands are also considered stable in parts of Canada and the western United States . Some stands, however, remain stable for decades but eventually deteriorate. Deteriorating stands are often succeeded by conifers, but shrubs, grasses, and/or forbs gain dominance on some sites . Succession to grasses and forbs is more likely on dry sites and is more common in the West than in the East . Quaking aspen readily colonizes after fire, clearcutting, or other disturbance . In Emigrant Wilderness Area, California, red fir (Abies magnifica) stands on north slopes have converted to quaking aspen after fire . In the Great Lakes States, quaking aspen has regenerated on cut/burned sites through sprouting and seedling establishment, becoming the dominant forest cover type . SEASONAL DEVELOPMENT : Quaking aspen catkins elongate before the leaves expand. In New England, catkins appear in mid-March to April; in the central Rockies, flowering occurs in May to June. Sustained air temperatures above 54 degrees Fahrenheit (12 deg C) for about 6 days apparently trigger flowering [55,123]. At high elevation, trees may flower before snow is off the ground . Female trees generally flower and leaf out before male trees. Local clonal variation produces early- and late-flowering clones of either sex, however. Catkins mature in 4 to 6 weeks (usually in May or June). Branches usually leaf out from early May to June . Seed dispersal in the Great Lakes States occurs from early May to mid-June, beginning earliest on protected sites and in southern portions of the region .
SPECIES: Populus tremuloides
FIRE ECOLOGY OR ADAPTATIONS : Fire adaptations: Quaking aspen is highly competitive on burned sites . Even where quaking aspen was a barely detectable component of the prefire vegetation, it often dominates a site after fire. Quaking aspen has adapted to fire in the following ways . 1. The thin bark has little heat resistance, and quaking aspen is easily top-killed by fire. 2. Root systems of top-killed stems send up a profusion of sprouts for several years after fire. 3. Sprouts grow rapidly by extracting water, nutrients, and photosynthate from an extant root system, and may outcompete other woody vegetation. 4. Following a fire, a new, even-aged quaking aspen stand can develop within a decade. 5. In contrast to most trees, quaking aspen is self-thinning. Without intervention, a mature forest of healthy trees can develop from dense sprouts. Fire releases sprout primorida on roots from hormonally controlled growth inhibition; removes canopy shade; and blackens the soil surface, increasing heat absorption. Increased soil temperatures aid sprout production [22,83]. On cold sites, quaking aspen may be unable to sprout until soil temperatures rise after fire . Quaking aspen is able to naturally regenerate without fire or cutting on some sites , but fire may be required for regeneration on others. There are areas in Jackson Hole, Wyoming, where ungulate browsing has been light, both historically and recently, yet stems have not attained tree size since extensive fires in the 1800's . Fuels and fire behavior: Fuels are usually more moist in quaking aspen stands than in surrounding forest. Crown fires in coniferous forests often drop to the surface in quaking aspen, or may extinguish after burning into quaking aspen only a few meters [19,55,138]. Quaking aspen stands often act as natural fuelbreaks during wildfires , and fires sometimes bypass quaking aspen stands surrounded by conifers . In an analysis of fires in quaking aspen in National Forests of the Intermountain West (USFS Regions 2, 3, and 4) from 1970 through 1982, Bevins  reported that wildfires that burned thousands of acres during extreme weather conditions usually penetrated less than 65 feet (20 m) into quaking aspen. Managers he interviewed used the terms "asbestos type" and "firebreak" to describe quaking aspen stands. Bevins reported that mixed quaking aspen-conifer types such as those on the northern Kaibab and Dixie National Forests did sustain fires, however, and burned substantial amounts of quaking aspen. Throughout all three Regions, a relatively few, large fires (>100 acres burned) accounted for 93.2 percent (or 1.12 million acres) of all quaking aspen burned. Fire history: Before and during the mid-nineteenth century, fires were apparently more frequent, and larger acreages of quaking aspen and quaking aspen-conifer mixes burned, than any time since. A large majority of the quaking aspen stands in Jackson Hole, Wyoming, date from fires between 1850 and 1890 . In central Utah, Baker  and Meinecke  found few quaking aspen fire-scarred later than 1885. Earlier fire scars were common and showed a 7- to 10-year fire frequency. Since quaking aspen is fire-sensitive, the fires were probably of low severity. Extensive sampling of quaking aspen in Colorado found few fire scars dating later than about 1880 . These data indicate that there has been a great reduction of fire rejuvenation of quaking aspen in the West since about 1900. Extensive young stands of quaking aspen are uncommon in the West [65,151,46]. Conifers now dominate many seral quaking aspen stands. Probable contributing factors are: 1. highly effective direct control of wildfires in the last 50 years, especially in the quaking aspen type , 2. reduction of fine fuels in quaking aspen/grass and quaking aspen/forb types due to grazing [28,46], and 3. cessation of deliberate burning by Native Americans [9,68,80]. Ungulates, fire, and quaking aspen: In most areas, ungulate browsing is probably not a major factor restricting postfire quaking aspen regeneration. Quaking aspen has increased in importance in the East despite browsing pressure from large white-tailed deer populations. In many areas of the United States, elk populations impact quaking aspen very little. Browsing elk had no significant impact on quaking aspen sprout density after wildfire in New Mexico . In some areas, however, fire suppression coupled with heavy ungulate browsing has reduced quaking aspen regeneration. Failure of some stands in the Great Lakes States to regenerate has been attributed to overbrowsing of sprouts by white-tailed deer . Overbrowsing has particularly been noted in northwestern Wyoming, in Yellowstone and Grand Teton National Parks and the Bridger-Teton National Forest. Elk are the primary browsers of quaking aspen in this area, although where moose populations are high, moose have also removed considerable quaking aspen regeneration. Historic narratives and photographic evidence suggest that ungulates were a major biotic influence on quaking aspen in this region during the exploration and settlement periods. However, fires were extensive during this period, so postfire sprouting of quaking aspen and growth of palatable grasses, shrubs, and herbs, probably produced a forage supply that dispersed browsing ungulates sufficiently for quaking aspen to regenerate . Coring of old quaking aspen stems in Yellowstone National Park showed that most live, large quaking aspen established in a brief period between the 1870's and 1880's: a period of severe fires followed by above-normal precipitation. Elk, moose, and beaver populations were at a historic low, and some wolves were present. Neither this combination of conditions nor significant quaking aspen regeneration has occurred since then. Elk populations were low in the 1950's and 1960's, but fires were suppressed and the climate was dry. In the 1910's, there were numerous elk and beaver and few fires. After the 1988 fires, elk numbers were high and climatic conditions were dry. In this region, even large-scale burning does not seem sufficient for quaking aspen regeneration [69,90,137]. Prairie: Frequent fires on prairies and plains grasslands historically helped control quaking aspen invasion . Fire may have been only one of several factors controlling quaking aspen, however. Drought  and ungulate browsing may have worked in conjunction with fire to curtail woody plant invasion. Fire alone may not control quaking aspen spread . Anderson and Bailey  reported that 24 years of annual spring burning checked quaking aspen invasion onto tallgrass prairie, but actually increased the number and cover of quaking aspen sprouts in the area. Elk Island National Park, Alberta, was described by early settlers as a grassland with scattered quaking aspen groves. By 1895, extirpation of bison and severe reduction of other ungulates was followed by expansion of quaking aspen. Bison were reintroduced with Park establishment, but fire was not. Ungulate populations rose rapidly and were culled in the 1930's and 1950's. Grassland expanded with the ungulates, while quaking aspen expanded when culling occurred . FIRE REGIMES : Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes". POSTFIRE REGENERATION STRATEGY : Tree with adventitious-bud root crown/soboliferous species root sucker Initial-offsite colonizer (off-site, initial community)
SPECIES: Populus tremuloides
IMMEDIATE FIRE EFFECT ON PLANT : Small-diameter quaking aspen is usually top-killed by low-severity surface fire . Brown and DeByle  found that as dbh increases beyond 6 inches (15 cm), quaking aspen becomes increasingly resistant to fire mortality. Large quaking aspen may survive low-severity surface fire, but usually shows fire damage [26,94]. Moderate-severity surface fire top-kills most quaking aspen, although large-stemmed trees may survive. Some charred stems that survived low- or moderate-severity fire initially have been observed to die within 3 or 4 postfire years. Severe fire top-kills quaking aspen of all size classes. Moderate-severity fire does not damage quaking aspen roots insulated by soil. Severe fire may kill roots near the soil surface or damage meristematic tissue on shallow roots so that they cannot sprout. Deeper roots are not damaged by severe fire and retain the ability to sucker [69,160,143,146]. Mortality does not always occur immediately after fire. Sometimes buds in the crown will survive and leaf out prior to the death of the tree . Brown and DeByle  reported that quaking aspen trees died over a 4-year period following fires in Wyoming and Idaho, although most individuals succumbed by the second postfire year. Even when quaking aspen is not killed outright by fire, the bole may be sufficiently damaged to permit the entrance of wood-rotting fungi . According to Jones and DeByle , basal scars which lead to destructive heart rot can be made on even good-sized aspen by "the lightest of fires." Basal fire scars may also permit entry of borers and other insects which can further weaken the tree . DISCUSSION AND QUALIFICATION OF FIRE EFFECT : Fire may kill (as opposed to top-kill) a deteriorating stand of quaking aspen. A deteriorating stand on the Sweetwater drainage of the Wind River Mountains, Wyoming, failed to sprout following a 1963 wildfire. However, another 1963 wildfire in the Wind River Mountains, near Pinedale, had the opposite effect on a deteriorating stand of quaking aspen. Although the site was considered poor for quaking aspen due to dry, sandy soil, fire only top-killed the stand. Browsing pressure on sprouts was light, and postfire stocking was "more than adequate" for regeneration . The position of an individual tree on a slope, or within a stand, can influence the degree of damage caused by fire. Even when damaged, trees located near the boundaries of a fire can often maintain a live crown. These peripheral trees may receive food supplies from the roots of unburned neighbors. Quaking aspen on slopes generally show greater damage than do trees on flatter areas. Flames moving uphill often curl up the lee side of trees when fanned by upslope wind, charring the stem further up its bole. The effect of slope is particularly pronounced (up to 31-44% higher char heights) after fires of higher severity. This relationship is presented in the following table : Probability of mortality ________________________ 0.90 0.95 ________________________ dbh (cm) Average char height - 10 5 12 15 14 21 20 23 30 25 32 39 Uphill char height - 10 6 16 15 19 29 20 31 42 25 44 55 PLANT RESPONSE TO FIRE :
|A prescribed fire in a black spruce-paper birch-quaking aspen community in boreal Alaska. Photo courtesy of US Forest Service, FROSTFIRE.|
Quaking aspen sprouts from the roots and establishes from off-site, wind-blown seed after fire [27,123,157]. It is the classic soboliferous species described by Stickney : a plant that sprouts from carbohydrate-storing lateral roots (sobols). Sprouting: Quaking aspen generally sprouts vigorously after fire. Long-term growth and survival of quaking aspen sprouts depend on a variety of factors including prefire carbohydrate levels in roots, sprouting ability of the clone(s), fire severity, and season of fire. Moderate-severity fire generally results in dense sprouting. Fewer sprouts may be produced after severe fire. Since quaking aspen is self-thinning, however, sprouting densities are generally similar several years after moderate and severe fire. A low-severity surface fire may leave standing live trees that locally suppress sprouting, resulting in an uneven-aged stand [12,13,28,123]. Quaking aspen burned in spring generally sprouts later in the growing season and again the following year. Fires in mid-growing season generally result in late-season sprouting. Quaking aspen burned in late summer or fall usually sprouts the next spring . Predicting postfire sprouting: Applying prescribed fire in exclosures in Yellowstone National Park, Renkin and Despain  found that root biomass can be estimated from basal area, and both can be used to predict local response of quaking aspen to burning. Sprout biomass produced in postfire year 1 was positively correlated (r2=0.90, p=0.013) with both prefire basal area and root biomass. On average, 11.5 metric tons per hectare of root mass were required to produce 0.1 metric ton per hectare of sprouts. Average sprout height was positively correlated with basal area and root biomass (r2=0.85, p=0.004). On average, 25 square meters per hectare of basal area and/or 19 metric tons per hectare of root biomass were required to produce 0.5 meter of sprout growth. Examples of sprouting: After the 1988 fires in Yellowstone National Park, percentage of sprouts produced in spring, 1989, was significantly higher (p=0.030) in burned stands (mean 82%) than on unburned stands (mean 60%). The percentage of sprouts in fall, 1989, was also higher (p=0.103) on burned stands (mean 82%) than in unburned stands (mean 65%). In spring 1990, sprout density averaged 80,000 stems per hectare in burned stands and 27,000 stems per hectare in unburned stands. By fall 1991, density was 38,000 stems per hectare in burned and 25,000 stem per hectare in unburned stands, respectively. Mean heights were 9.6 inches (24 cm) in spring 1990 and 10.8 inches (27 cm) in spring 1991. Browsing intensity was much higher in winter and spring (45-55% of sprouts browsed) than summer and fall (5-10%). There were no significant differences in browsing among burned stands, unburned stands adjacent to burned stands, and remote unburned stands: Sprouts were heavily browsed in all stand types . Birch-aspen: Following a 1944 summer wildfire in Maine, quaking aspen and paper birch sprouted vigorously, forming a dense stand. In 1951, there were 40,000 to 45,000 stems (both spp.) per acre. Quaking aspen dominated the stand; it averaged 20 feet (6 m) in height while paper birch averaged only 6 feet (1.8 m) . Birch-aspen: Following a 1944 summer wildfire in Maine, quaking aspen and paper birch sprouted vigorously, forming a dense stand. In 1951, there were 40,000 to 45,000 stems (both spp.) per acre. Quaking aspen dominated the stand; it averaged 20 feet (6 m) in height while paper birch averaged only 6 feet (1.8 m) . Southwestern mixed conifer: Quaking aspen sprouted after the Walker Wildfire on the Santa Fe National Forest of New Mexico. The Walker Fire occurred in mixed-conifer forest with an overstory of Engelmann spruce (P. engelmannii), Douglas-fir (Pseudotsuga menziesii), quaking aspen (Populus tremuloides), and ponderosa pine (Pinus ponderosa). The litter layer was deep prior to the wildfire. The fire was a moderate-severity surface fire that consumed understory conifers and hardwoods (mainly quaking aspen). Overstory foliage was killed by heat from the surface fire. The Walker Fire top-killed most of the quaking aspen stems. Eighteen months after the fire, 1 acre of the Walker Burn was fenced to exclude deer, elk, and cattle. Wildfire significantly increased the number of quaking aspen sprouts. Five-year average sprout density was 12,960 sprouts per acre on the burn compared to 100 sprouts per acre in adjacent unburned forest and 200 and 500 sprouts per acre on similar spruce-fir types in Arizona.
In 1964, quaking aspen sprouts on the burn were less then 3 feet (0.9 m) tall, so ungulates could browse them easily. By June 1968, sprouts were 8 to 10 feet (2.4-3 m) tall, and getting out of reach as a food supply. Cattle and wildlife use on the burned area did not significantly affect quaking aspen sprout density; the number of sprouts was similar inside and outside the exclosure . For further examples of quaking aspen sprouting response after fire, refer to the FIRE CASE STUDIES section. Cases from Arizona, Colorado, Wyoming, Minnesota, and Alberta are presented. Seedling Establishment: Fire exposes mineral soil, which is an excellent seedbed for quaking aspen . Quaking aspen seedlings have been noted following severe fire in Canada. Six years after fire in northeastern Wisconsin, quaking aspen seedlings composed 20 to 35 percent of seedlings of all species present on the burn . Kay  reported good seedling establishment following 1986 fires in Grand Teton National Park and 1988 fires in Yellowstone National Park. Height growth was negligible, however, due to ungulate browsing. Density, height, and ungulate use of quaking aspen seedlings on the Yancy's Hole Burn, Yellowstone National Park, were : _____________________________________________________________________ Transect # Year Number/ha % browsed Mean height (cm) 1 1989 177,202 -- 62 1991 32,154 100 50 2 1989 141,362 -- 60 1991 46,148 100 57 3 1989 109,522 -- 53 1991 16,660 100 75 __________________________________________________________________ Mean 1989 142,695 -- 58 1991 31,654 100 47 Renkin and others  are conducting a similar seedling study on forested and nonforested sites in Yellowstone National Park; only preliminary data are available at this time. They found that quaking aspen seedlings were concentrated on wet microsites but widely scattered on other site types. In 1989, quaking aspen seedling density on 14 plots ranged from 0.6 to 1,014 per square meter; average height ranged from 2.3 to 11.1 inches (mean=5.1 inches) (5.7-27.8 cm, mean= 12.8 cm). Quaking aspen seedlings were two to four times taller than lodgepole pine seedlings on forested plots. In 1990, all plots had persistent quaking aspen seedlings; in some cases the stem had died back but the 1-year-old roots had produced suckers. Density of surviving seedlings ranged from 0.05 to 332 per square meter. Average heights had increased, ranging from 3.6 to 15.6 inches (mean=7.8 in) (9-39 cm, mean=19.4 cm). Quaking aspen seedlings on fenced plots averaged 12 inches (30 cm) in height; seedlings on unfenced plots averaged 5.36 inches (13.4 cm). Seedling survival was significantly greater (p=0.004) on forested than nonforested plots. Survival was also influenced by presence of ungulates, spring flooding, disease, and intraspecific competition. Ungulate presence negatively influenced seedling survival on unfenced plots (r=0.97, p=0.004). Plots submerged in spring showed high seedling mortality. A fungus (Venturia tremulae) also contributed to seedling death or dieback . DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : These Research Project Summaries provide information on prescribed fire use and postfire response of plant species associates in quaking aspen communities:
From the Colorado fire study just above, the Fire Case Study Prescribed fire behavior and quaking aspen recovery in Colorado's Front Range provides a more detailed description of prescribed fire's effects on quaking aspen. For further information on quaking aspen response to fire, see the other Fire Case Studies in this species summary. FIRE MANAGEMENT CONSIDERATIONS : Prescribed fire is recommended for quaking aspen [2,25,123,143]. Currently, an estimated 600 acres (240 ha) of quaking aspen burns per year in the Intermountain Region. At that rate, it will require 12,000 years to burn the entire quaking aspen type in that Region. It is likely that seral quaking aspen will be replaced by conifers; stable quaking aspen stands may become less productive . In many areas of the West, quaking aspen stands have lived longer than they did prior to fire exclusion, and many stands are in a state of decline due to advanced age . Gruell and Loope  found that in Jackson Hole, Wyoming, quaking aspen stands begin to deteriorate after about 80 years. Houston  stated in 1973 that quaking aspen in Yellowstone National Park were primarily large trees ranging from 75 to 120 years of age. Applying fire: Prescribed fire is often difficult to apply in quaking aspen stands because of the prominence of live fuels and often sparse distribution of fine dead fuels . Even if fuels are plentiful, they are usually too moist to burn easily. Prescribed fire may be possible, however, when live vegetation cures enough to contribute to fire spread rather than hinder it. The combination of dry weather and cured fuels occurs most often in early spring, late summer, and fall [131,138]. The forest floor of a quaking aspen stand immediately after snowmelt is covered by matted, cured surface vegetation and deciduous leaf litter. Before leaf-out this mat is directly exposed to drying by wind and sun, which increase fuel temperature and decrease fuel moisture. Without rain, the withered leaves in the litter begin to curl, resulting in a more favorable fuelbed for combustion and heat transfer. In Alberta, these moderately severe, early season burning conditions can persist from snowmelt until the first week in June . In most years, leaf fall and autumn precipitation coincide, making fall burning difficult. If September and October are dry, however, burning may be possible. Surface fuels are dead and sometimes frozen, with a continuous layer of loosely packed leaves, making quaking aspen more flammable than at any other time of year . Live fuel moisture varies greatly between understory species throughout the growing season, but can be estimated well enough to determine when to light prescribed fires. Brown and others  estimated that when herbaceous vegetation is the primary fine fuel, at least 50 percent curing is needed to sustain fire spread. Less than 50 percent curing may be sufficient in stands with substantial conifers. Brown and Simmerman  provide a method for appraising fuels and flammability in quaking aspen to assist managers in choosing when to apply prescribed fire and help determine proper conditions for burning. Five fuel types in 19 community types common in the Intermountain West are presented, accompanied by color photographs. Prescriptions: Aspen parkland and northern forest - Bailey [174,175] found that in Alberta, prescribed burning in quaking aspen forests and parklands in spring was usually not successful above relative humidity of 35 to 40 percent. He recommended that prescribed burning be conducted 8 to 10 drying days after snowmelt, when air temperature is at least 64 degrees Fahrenheit (18 deg C), relative humidity is less than 30 percent, and 3.3-foot (10-m) open winds are 5.4 to 21 miles per hour (9-35 km/hr). Bailey and Anderson  reported that in central Alberta, quaking aspen forest in a grassland-shrub-quaking aspen forest mosaic was the most difficult of the three vegetation types to prescribe burn. With spring burning, backfires consistently gave poor results, frequently going out within a few feet of ignition and yielding a maximum temperature of only 550 degrees Fahrenheit (288 deg C). Headfires were hotter but gave variable results. Most headfire temperatures ranged from 700 to 900 degrees Fahrenheit (371-482 deg C), but 14 percent were in excess of 1,112 degrees Fahrenheit (600 deg C). Fire and fuel data from the quaking aspen sites follow. ________________________________________________ | fire temperature 393 +/- 28* (deg C) | | total fuel 13,436 +/- 354 (kg/ha) | | ground fuel 11,704 +/- 337 (kg/ha) | | standing woody fuel 1,732 +/- 181 (kg/ha) | |______________________________________________| *standard error of the mean (SEM) Perala  recommended this prescription for burning quaking aspen slash in the Great Lake States: ______________________________________________________________________ Months for burning dormant season (all but June, July, & August) Fuel model* D Air temperature > 65 degrees Fahrenheit (18 deg C) Relative humidity < 35% Ignition component* 40-50 Energy release component* 14-17 Spread component* 4-7 Burning index* 13-21 Wind** 2.5-5 m/s Number of days with less than 2.5 mm rain > 5 ______________________________________________________________________ *from the National Fire-danger Rating System  **measured 20 ft. above ground, or at average height of vegetation cover, averaged over at least a 10-minute period Canadian Forest Fire Behavior Prediction (FBP) System : Alexander and Maffey  provide examples for predicting fire spread rate, fuel consumption, and frontal intensity in quaking aspen types using the FBP System. Forage quality and fire: Three burned quaking aspen/shrub/tall forb communities on the Caribou National Forest, Wyoming, showed increased forage quality (better Ca:P ratios, higher elk digestibility, and higher crude protein and P levels) than adjacent unburned sites during the first postfire year. By the second postfire year, there were no significant differences between forage quality on burned and unburned sites. Shrubs on the unburned sites were above browse level throughout the study period, however, while shrubs on the burned site were still accessible to elk in the second postfire year .
Howard, Janet L., compiler. 1996. Overstory mortality of quaking aspen after repeat spring prescribed fire in central Alberta. In: Populus tremuloides. 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/ [ ].
Quintilio, D.; Alexander, M. E.; Ponto, R. L. 1991.
Spring fires in a semimature trembling aspen stand in central Alberta.
NOR-X-323. Edmonton, AB: Forestry Canada, Northwest Region, Northern Forestry Centre. 30 p. .
spring, May 9-15, 1972/low to moderate
spring, May 5, 1978/severe
The study site is approximately 120 miles (200 km) north of Edmonton, Alberta, and about 3.6 miles (6 km) northwest of Hondo, Alberta (latitude 50 deg 06 min N and longitude 114 deg 08 min W). It is located in NE Section 30, Range 2, Township 70, west of the Fifth Meridian. The study site lies within a fire research reserve in the Slave Lake Forest.
The study area is within boreal mixed-wood forest. The site is
surrounded by open, grassy muskeg with some black spruce (Picea
mariana). The stand was dominated by quaking aspen (Populus
tremuloides). Height and dbh of quaking aspen stems averaged 50 feet
and 4.4 inches (13 m and 11 cm), respectively. Stand basal area
averaged 29.38 sq m/ha (SD = +/- 5.61). Live and dead tree densities
averaged 2,802 (SD = +/- 980) and 916 (SD = +/- 581) stems/ha,
respectively. Quaking aspen made up 99 percent of the basal area and 98
percent of the stand density. The site also contained scattered white
spruce (Picea glauca) and jack pine (Pinus banksiana) and infrequent
clumps of paper birch (Betula papyrifera). Tall understory shrubs
included American green alder (Alnus viridis spp. crispa), pin cherry
(Prunus pensylvanica), and beaked hazel (Corylus cornuta). Dominant
herbs were twinflower (Linnaea borealis), cream peavine (Lathyrus
ochroleucus), wild sarsaparilla (Aralia nudicaulis), dwarf red
blackberry (Rubus pubescens), and bunchberry (Cornus canadensis).
Litter mass averaged 0.30 +/- 0.09 kg/sq m. Woody fuels averaged 0.369 kg/sq m: scant compared to other forest cover types of Alberta. Consequently, downed-dead woody fuels contributed little to behavior or effects of the 1972 fires.
Spring leaf-out had not yet occurred.
The study site is well drained. Soils are loam underlain with deep
layers of coarse and fine sand. Topography is strongly undulating with
a slope of less than 10 percent. Elevation is 1,947 feet (590 m).
Plots: A 12-meter firebreak was bulldozed around eight 45 X 100 meter blocks. The eight blocks were separated by 6- or 12-meter, bulldozed strips. Each block was subdivided into three plots.
Thirteen plots were burned in sequence during a 7-day period in spring 1972. The first plot was burned on May 9, which was as soon after snowmelt as fuels could support a slow-moving fire. Burning continued until May 15, utilizing weather variations during that time. For all plots, headfires were ignited from early to mid-afternoon from an established line source. Ranges of weather variables were:
|temperature||57-75 deg F (13.9-23.9 deg C)|
|average wind speed*||0.48-2.5 miles/hr (0.8-4.2 km/hr)|
|length of time after a significant** rain||3-9 days|
|*Measured 4.6 feet (1.4 m) above ground at time of fires.|
|** > 1.05 mm.|
Reburning was done on May 5, 1978. One and one-half plots were reburned. Weather conditions were:
|temperature||60 deg F (15.5 deg C)|
|average wind speed*||4.0 miles/hr (6.6 km/hr)|
|length of time after a significant** rain||6|
|*Measured 4.6 feet (1.4 m) above ground at time of fires.|
|** > 1.05 mm.|
Fire-danger conditions according to the Canadian Fire Weather Index
ranged from low to high during the 1972 fires. Most of the range in
fire danger was due to variations in wind speed. Test fires ignited on
May 7 and 8, 1972, were not sustainable with dead fine fuel moistures of
70 and 85 percent and initial spread indices (ISI) of 0.5 and 2.0 (i.e.,
with no wind). All remaining fires spread uniformly over the plots,
suggesting that an ISI between 2.0 and 2.5 is a threshold condition for
sustained fire spread in the leafless quaking aspen fuel type. Rate of
headfire spread ranged from 0.28 to 2.51 m/minute. Flame height ranged
from 0.3 to 3.3 feet (0.1-1.0 m); fireline intensities were "low to
moderate," ranging from 15 to 390 kW/m. All the 1972 prescribed fires
had a fairly easy difficulty of control rating (I < 500 kW/m). Fuel
consumption averaged 0.35 kg/sq m.
The 1978 fires were intense, mainly due to an increase in surface fuels (mostly dead quaking aspen) after the 1972 fires. Average rate of headfire spread was 4.6 m/minute, nearly double that of the most intense 1972 fires. Fireline intensity was 4,392 kW/m, equal to a high-intensity surface fire or intermittent crown fire in a conifer forest stand. Fuel consumption averaged 3.4 kg/m sq. Fuel consumption and fire behavior data follow.
|Experimental fire plot number||Fuel consumption* (kg/sq m)||Energy per unit area (kJ/sq m)||Headfire rate of spread (m/min)||Fireline intensity (kW/m)|
|*Includes downed-dead woody surface fuels, cured surface vegetation, leaf litter, and F and H litter layers.|
|**Plots reburned in 1978.|
After the 1972 low-intensity fires, mortality in the quaking aspen overstory ranged from 0 to 100 percent, with top-kill averaging 29 percent. After the 1972 moderate-intensity fires, overstory mortality again ranged from 1 to 100 percent. Average top-kill was 56.5 percent. Large-diameter stems (> 7 inches [17.5 cm] dbh) were more likely to survive both low- and moderate-intensity fire. Stems greater than 8 inches (20 cm) dbh were not top-killed. The intense, 1978 reburns top-killed all small- (1 to 4 inches [2.5-10.0 cm] dbh) and medium-sized (4 to 6 inches [10.0-17.5 cm] dbh) stems, and all but a few of the large stems. Quaking aspen stem mortality data are:
|dbh size classes||moderate-intensity fires||low-intensity fires||1978 reburn|
|stem size (cm)||block 3c||block 4||block 5||plots 3b & c||unburned controls|
|All size classes||45||68||29||97||15|
There are few data on fire behavior in relation to burning conditions in quaking aspen types. This study provides information on fire behavior including headfire rate of spread, fuel consumption, fireline intensity, and fire effects on quaking aspen forests in the boreal zone. Additionally, prefire fuel moisture conditions and impact of burning on the forest floor (depth of burn and forest floor reduction) are given. Pre- and postfire frequency and cover data for understory species are also presented.
Tirmenstein, D. A., compiler. 1989. Prescribed fire temperatures and effects in a central Alberta quaking aspen forest. In: Populus tremuloides. 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/ [ ].
Anderson, Murray L.; Bailey, Arthur W. 1979. Effect of fire on a Symphoricarpos occidentalis shrub community in central Alberta. Canadian Journal of Botany. 57: 2820-2823. .
Bailey, Arthur W.; Anderson, Murray L. 1980. Fire temperatures in grass, shrub and aspen forest communities of central Alberta. Journal of Range Management. 33(1): 37-40.  .
Spring (May 1977)/severity not reported
The study area was located at the University of Alberta Ranch, 91 miles (152 km) southeast of Edmonton, Alberta .
The landscape was a mosaic of quaking aspen (Populus tremuloides) forest, western snowberry (Symphoricarpos occidentalis) shrubland, and rough fescue-Canadian needlegrass (Festuca scabrella-Stipa curtiseta) grassland. Differences in plant species composition between the three community types were not described in detail. Western snowberry and willows (Salix spp.) were present in the quaking aspen understory and were important fuels. Other shrubs common on the landscape included roses (Rosa acicularis, R. woodsii), grayleaf red raspberry (Rubus idaeus var. strigosus), Canadian gooseberry (Ribes oxyacanthoides), silverberry (Elaegnus commutata), and cherries (Prunus pensylvanica, P. virginiana). In quaking aspen forest, shrubs were most common on the forest edges. Interior portions of the quaking aspen forest understory were dominated by unspecified forbs [2,3].
Topography is moderately to strongly rolling. Loamy black and dark brown chernozemic soils overlay glacial till .
Standing woody fuels were most plentiful near the margins of quaking
aspen groves, where small quaking aspen stems were interspersed with
western snowberry. Ground fuels were more sparse on forest margins than
on the forest floor. The duff layer was either wet or frozen .
The quaking aspen, western snowberry, and grassland communities were prescribed burned with backfires and headfires. Quaking aspen forest was the most difficult of the three communities to prescribe burn; only half the quaking aspen forest burned. However, it had the greatest range of fire temperatures. Headfires were hotter than backfires in all three communities; backfires usually went out within a few feet of ignition in quaking aspen forest. Fire temperatures at the soil surface were greatest (in excess of 1,112 degrees Fahrenheit [600 deg C]) on forest margins, where dead willow and quaking aspen branches had accumulated and stands of live western snowberry were dense. Fire temperature and fuel data for the quaking aspen community follow .
total available fuel - 11,824 pounds/acre (13,436 kg/ha)
ground fuel - 10,300 pounds/acre (11,704 kg/ha)
standing woody fuel - 1,524 pounds/acre (1,732 kg/ha)
fire temperature (mean) at soil surface - 739 degrees Fahrenheit (393 deg C)
backfire - 442 degrees Fahrenheit (228 deg C)
headfire- 806 degrees Fahrenheit (430 deg C)
fire temperature (range) at soil surface
backfire - 119-670 degrees Fahrenheit (93-371 deg C)
headfire - 500-1,800 degrees Fahrenheit (260-982 deg C)
total area burned (mean) - 53%
backfire - 29%
headfire - 65%
Backfires had very little effect on quaking aspen since they extinguished within a few feet after entering quaking aspen forest. Effect of headfires on quaking aspen was variable. Some quaking aspen stems were top-killed by headfires; percentage top-kill was not given. All recorded temperatures at the soil surface were in excess of 140 degrees Fahrenheit (60 deg C), the lethal temperature for plant tissues. Duration of high temperatures influences mortality of plant tissues, however, and temperature duration was not measured. Where top-kill approached 100 percent, survivors were usually protected from fire by topographic relief .
Quaking aspen forest was difficult to burn. Range of fire temperatures was wide depending upon type and distribution of fuels, weather, topography, and method of ignition. Higher temperatures were reached where downed woody fuels (mostly willows and western snowberry) had accumulated or in dense stands of live western snowberry. Backfires were not successful. Headfires produced a wide range of temperatures. Headfires were most successful (produced nearly 100% top-kill of quaking aspen) when surface fuels were very dry, relative humidity was low, and winds were in excess of 3.6 miles per hour (6 km/hour) .
Howard, Janet L., compiler. 1996. Quaking aspen productivity after harvest and repeat prescribed fire in Minnesota. In: Populus tremuloides. 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/ [ ].
Deeming, John E.; Lancaster, James W.; Fosberg, Michael A.; [and others]. 1974. National fire-danger rating system. Res. Pap. RM-84. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 53 p. .
Perala, Donald A. 1974. Repeated prescribed burning in aspen. Res. Note NC-171. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 4 p. .Perala, Donald A. 1974. Growth and survival of northern hardwood sprouts after burning. Res. Note NC-176. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 4 p. .
Perala, Donald A. 1974. Prescribed burning in an aspen-mixed hardwood forest. Canadian Journal of Forest Research. 4: 222-228. .
Perala, Donald A. 1979. Regeneration and productivity of aspen grown on repeated short rotations. Research Paper NC-176. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 7 p. .
Perala, D. A. 1995. Quaking aspen productivity recovers after repeated prescribed fire. Res. Pap. NC-324. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 11 p. .
spring (May 17, 1967)/severe
spring (May 13, 1969)/low
fall (October 5, 1970)/moderate to severe
The stand was commercially harvested 2 years before the first prescribed
fire. Before harvest, the stand was dominated by 60-year-old quaking
aspen (Populus tremuloides). Site basal area was 30 sq m/ha; basal
area of quaking aspen was 22 sq m/ha. The rest of the stocking was
mostly hardwoods including basswood (Tilia americana), sugar maple (Acer
saccharum), red maple (A. rubrum), paper birch (Betula papyrifera),
ironwood (Ostrya virginiana), northern red oak (Quercus rubra), bur oak
(Q. macrocarpa), and American elm (Ulmus americana). Some balsam fir
(Abies balsamea), white spruce (Picea glauca), and eastern white pine
(Pinus strobus) were present. Successional trend was toward sugar
maple-basswood. Understory shrubs included pin cherry (Prunus
pensylvanica), chokecherry (P. virginiana), Allegheny serviceberry
(Amelanchier laevis), alternate-leaf dogwood (Cornus alternifolia),
red-osier dogwood (C. sericea), willows (Salix spp.), downy arrowwood
(Viburnum rafinesquianum), and eastern leatherwood (Dirca palustris)
About 74 t/ha of quaking aspen averaging 7.6 inches (19 cm) dbh was harvested. Associated hardwoods were not harvested: with an average dbh of 5.6 inches (14 cm), they were not considered merchantable. Conifers were harvested. After harvest, slash fuels covered 47 percent of the area at a mean depth of 10.8 inches (27 cm), with a few accumulations up to 5 feet (1.5 m) [121,119].
Plots: Twelve 1-hectare blocks were established in the harvest area. On three blocks, overstory trees left after harvest were felled, creating a clearcut. The other nine blocks were targeted for prescribed burning .
The soils are considered good for quaking aspen: a Warba very fine sandy loam with clayey loam subsoil. Elevation is 1,312 to 1,345 feet (400-410 m). Topography is level to gently rolling. Climate is continental with mean annual precipitation of 24.4 inches (610 mm) and mean July temperature of 68 degrees Fahrenheit (20 deg C) [119,124].
Burning conditions - 1st prescribed fire: Suitable burning conditions
did not occur until 2 years after logging, on May 17, 1967. The cured
slash was burned with 50- to 100-foot-strip (15- to 30-m) headfires
after backfiring downwind sides. Hardwoods not killed by the fire, and
unharvested hardwoods in the control (no burn) area, were then felled .
Repeat fires: Two and four years (May 13, 1969, and Oct. 5, 1970) after the first burn, separate parts of the burn area were burned again using 50- to 100-foot-strip (15- to 30-m) headfires after backfiring the downwind side of the burn area . Weather and fire indices for each fire according to the National Fire-Danger Rating System  were [120,119]:
|Variables||17 May 1967||13 May 1969||5 October 1970|
|Air temperature (deg F)|
|Relative humidity (%)||29||32||35|
|Wind speed (m/s)||5||6||6|
|1-h time lag (TL) fuel moisture(%)||5||5||5|
|10-h TL fuel moisture (%)||6||7||7|
|fine fuel moisture (%)||6||6||8|
|Energy release component||16||7||6|
|*Percent, by volume, of living fine fuels.|
Fire behavior - 1st fire (1967): The first, slash-fueled fire was
intense. At one point it escaped the fireline, burning a treatment
block intended as a control. The fire was later estimated to be "nearly
uncontrollable." Nearly all fuels less than 3 inches (7.6 cm) in
diameter were completely consumed. Few coarse fuels burned.
Approximately 25 minutes were required to burn each 1-hectare replicate;
rate of fire advance averaged 4.2 cm/s. Fireline intensity in slash was
estimated at 138 kW/m. Intensity in litter was not measured but was
"minor in comparison." Litter fuels carried fire between slash
accumulations so that burn coverage was complete .
Repeat fires (1969 and 1970): The spring repeat fire was considered only partially effective, whereas the fall repeat fire was highly effective . The spring fire crept along the layer of litter and herbaceous vegetation matted down by winter snow. Decomposed organic layers were still wet and did not burn. Burn coverage was 76 percent. Flame heights were just a few decimeters, giving a fireline intensity of about 10 kW/m [120,119,124].
In the fall, the forest floor was drier. Standing vegetation carried the fire well and burn coverage was 85 percent. Flame heights were from 1 to 2 feet (0.3-0.6 m), giving a fireline intensity of 20 to 100 kW/m. The forest floor was completely consumed on 10 percent of the area, exposing mineral soil [120,124].
Short-term effects - first prescribed fire: The fire top-killed all
woody regeneration including quaking aspen sprouts. Seventy-six percent
of the hardwood overstory was top-killed: of an average 6.9 sq m/ha
basal area of overstory hardwoods standing after harvest, only 1.7 sq
m/ha were alive after fire [120,119]. Some quaking aspen roots were killed
or injured by intense heat .
One year after the fire, quaking aspen sprout density on the burn was 85 percent higher than on the clearcut .
Repeat treatments: The spring and fall prescribed fires top-killed quaking aspen. Some quaking aspen roots were killed by the fall fire. Postfire quaking aspen seedling establishment was noted where mineral soil was exposed, although seedling density was not recorded. Quaking aspen sprout densities on the burns were [120,119]:
|1967 single (spring) fire||25,000||18,000||16,000||13,000||11,000||9,500|
|1969 repeat spring fire||----||17,500||10,000||8,000||7,000||6,000|
|1970 repeat fall fire||----||----||----||13,000||25,000||14,000|
Quaking aspen productivity (stand yield with respect to stand age) was reduced in the short term by repeated prescribed fire. Parent roots, damaged by the first fire, were further stressed by initiating another crop of sprouts [119,124]. Volume growth of quaking aspen was :
|1967 single (spring) fire||20||60||80||130||160||210|
|1969 repeat spring fire||----||60||50||75||95||140|
|1970 repeat fall fire||----||----||----||130||23||42|
Long-term effects: Perala  has monitored these study sites for 25 years. He concluded that in the long term, quaking aspen yield was similar with clearcutting, repeat spring fire, or repeat fall fire. The single prescribed fire treatment reduced quaking aspen. Even after 25 years, productivity had not recovered to prefire levels. Repeat burns, however, slowed growth and reduced yield of other hardwood species, enhancing the quaking aspen component of the stand. Repeat fall burning enhanced quaking aspen productivity the most: On repeat fall burn plots, quaking aspen productivity at postfire year 25 was 111 percent of unburned quaking aspen. Modelling productivity, Perala  found that standing crop after 25 years was:
|repeat spring burn||14.9||34.7||56.7||70.6|
|repeat fall burn||19.8||42.7||67.2||84.8|
|repeat spring burn||5.11||8.70||12.7||16.9|
|repeat fall burn||3.90||6.32||8.9||11.5|
There is a very narrow window for prescribed burning dormant quaking
aspen in northern Minnesota. Perala  predicted that the necessary
energy release component of 14 to 17 (see prescription in FIRE
MANAGEMENT) would occur during only 2.8 days of the dormant season. In
this study, two attempts to burn 11 and 17 months after harvest were
unsuccessful because of high humidity, low wind speed, or low
Because of their readily released energy, fuels less than 2.8 inches (7 cm) in diameter were the most important fuel component to fire spread. Postfire quaking aspen sprouting was greatest where cured fuels were evenly distributed. Slash accumulations burned too hot and damaged roots, which reduced sprouting. Areas without slash reduced burn coverage, which favored other hardwood species .
This study shows that even on a productive site, long-term quaking aspen productivity can be reduced by an intense fire resulting from burning heavy slash. Repeat fall burning may ameliorate the effects of a single, intense fire by favoring the quaking aspen component of the stand over associated hardwoods .
Howard, Janet L., compiler. 1996. Quaking aspen sprouting density and elk use after prescribed fire in Wyoming. In: Populus tremuloides. 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/ [ ].
Bartos, Dale L.; Brown, James K.; Booth, Gordon D. 1994. Twelve years biomass response in aspen communities following fire. Journal of Range Management. 47: 79-83. .
Bartos, Dale L.; Mueggler, Walter F. 1979. Influence of fire on vegetation production in the aspen ecosystem in western Wyoming. In: Boyce, Mark S.; Hayden-Wing, Larry D., eds. North American elk, ecology, behavior and management. Laramie, WY: University of Wyoming: 75-78. .
Bartos, D. L.; Mueggler, W. F. 1981. Early succession in aspen communities following fire in western Wyoming. Journal of Range Management. 34(4): 315-318. .
Bartos, Dale L.; Mueggler, Walter F.; Campbell, Robert B., Jr. 1991. Regeneration of aspen by suckering on burned sites in western Wyoming. Res. Pap. INT-448. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 10 p. .
Basile, Joseph V. 1979. Elk-aspen relationships on a prescribed burn. Res. Note INT-271. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 7 p. .
Brown, James K.; DeByle, Norbert V. 1987. Fire damage, mortality, and suckering in aspen. Canadian Journal of Forest Research. 17: 1100-1109. .
summer (Aug. 29, 1974)/low-severity to severe
The study site, Breakneck Ridge, is located on the upper drainage of the Gros Ventre River of the Bridger-Teton National Forest, approximately 29 miles (48 km) northeast of Jackson, Wyoming .
The landscape was a mosaic of quaking aspen (Populus tremuloides),
conifer (mostly subalpine fir [Abies lasiocarpa]), big sagebrush
(Artemisia tridentata), and grassland communities. Quaking aspen groves
were mostly on southwesterly to northwesterly slopes. Subalpine fir was
invading on northerly aspects [10,13]. Some
decadent quaking aspen
clones were being replaced by big sagebrush/grass. Quaking aspen sucker
density was approximately 14,000 per hectare. Suckers were mostly less
than 1 meter tall and suppressed by elk and moose browsing .
The shrub layer of the quaking aspen groves consisted of shrubby cinquefoil (Pentaphylloides floribunda), Wood's rose (Rosa woodsii), mountain snowberry (Symphoricarpos oreophilus), and quaking aspen sprouts. Slender wheatgrass (Elymus trachycaulus), fringed brome (Bromus ciliatus), sticky geranium (Geranium viscosissimum), lodgepole lupine (Lupinus parviflorus), woodland strawberry (Fragaria vesca), fireweed (Epilobium angustifolium), and Fendler's meadowrue (Thalictrum fendleri) were common in the herbaceous understory [10,12].
Grazing use: The study site lies along an elk migration route. Elk use of the area is severe in fall, winter, and spring. Cattle graze the area three summers out of four on a rest-rotation system .
Plots: Ten quaking aspen clones (0.8 to 2 acres [2-5 ha] each) were selected for study. Nine clones were targeted for burning. A firebreak was established around the most southerly clone for an unburned control. Four permanent 10 X 10-meter macroplots were established in each clone, for a total of 40 macroplots [10,13].
The fire was conducted during the growing season. The flowering period was over and quaking aspen was fully leaved .
Aspect on the study sites is northwest to northeast, with a 14 to 42 percent slope. Elevation is 7,897 to 8,263 feet (2,393-2,504 m). Aspen site index (80 yr) was 40 to 65 .
The primary purpose of the prescribed fire was to produce more quaking
aspen suckers than elk could consume, and thus perpetuate the quaking
aspen stands . The area was burned on August 29, 1974. Weather
conditions were :
air temperature: 77 degrees Fahrenheit (25 deg C) winds: 7.8-19.2 mi/hr (13-32 km/hr), gusty relative humidity: 18% fuel moisture: 10-45%
The area did not burn uniformly and a patchwork of fire severities resulted. Portions of the nine prescribed burned macroplots did not burn; other portions were lightly, moderately, or severely burned. This was attributed to differences in amount of dry fuel on the ground and differences in moisture content of duff and understory vegetation due to slight differences in exposure .
Of the 36 burned macroplots (4 were controls), 11 were lightly burned, 13 were moderately burned, and 12 were severely burned. Light burns were defined as those removing less than 21 percent of litter and duff; moderate burns removed 21 to 80 percent, and severe burns removed 81 to 100 percent of litter and duff .
More than 90 percent of the quaking aspen overstory was killed on
severely burned sites. Top-kill on moderately burned sites was less than
90 percent .
Prescribed fire stimulated quaking aspen sucker production relative to the control. Sucker production peaked in postfire year 2. By postfire year 3, suckers on burned sites had thinned to about 30,000 per hectare as opposed to 17,000 per hectare on the control. After 3 years, both moderately and severely burned sites supported approximately the same number of sprouts .
Although fire stimulated sucker production, elk use of the suckers was heavy. Quaking aspen sucker densities 6 years after fire ranged from 4,300 to 10,300 per hectare for the three fire severities: approximately the same as before the fire. At postfire year 12, densities ranged from 1,500 to 2,400 suckers per hectare, which was 20 to 38 percent less than prefire densities. The control area had 5,150 suckers per hectare in 1986 compared to 8,500 per hectare that occurred prior to treatment. The 39 percent reduction of suckers on the control was attributed to elk use .
Average quaking aspen sprout density for 6 sample years follow .
|Control||8,500 (3,373)||18,625 (4,023)||16,750 (3,455)||18,625 (2,585)||12,250 (3,099)||5,150 (1,981)|
|Low||4,000 (1,452)||7,727 (2,322)||15,727 (4,093)||8,636 (2,140)||4,318 (1,995)||686 (1,854)*|
|Moderate||5,962 (1,535)||18,692 (5,121)||30,692 (8,528)||20,154 (5,230)||9,654 (2,376)||1,854 (712)*|
|Severe||8,417 (1,633)||7,333 (2,831)*||36,458 (7,114)||21,792 (3,889)||10,292 (2,839)||2,400 (589)|
|*Fire severity means followed by an asterisk are significantly different (p<0.10) from the control.|
After 12 years, the objective of producing more quaking aspen suckers
than elk could consume was not met. Enough suckers were produced
initially to reestablish the quaking aspen stands; however, most suckers
were eliminated or severely suppressed by heavy elk browsing. (Cattle
seldom browsed the quaking aspen suckers and appeared to have little
impact on quaking aspen.) Bartos, Brown, and Booth  have questioned
the use of prescribed fire in areas subject to heavy ungulate use. In
this case, rather than rejuvenate the quaking aspen stands, fire may
have sped up their deterioration.
Differences in browsing by clone: Postfire browsing varied by clone. Elk browsing in the winter of 1976 - 1977 averaged 44 percent of current growth and reduced average height of suckers by 28 percent. In 1977, height of tagged suckers had increased an average of only 1 percent over the previous year. Growth rates of 20 tagged quaking aspen suckers were :
|Mortality (%)||Utilization of current growth (%)||Height reduction from summer (%)||Unprotected (%)||Protected in exclosures (%)|
|*Unburned control clone.|
There were no significant differences between sucker density on sites
with different burn severities . In theory, moderate-severity fire
should produce the greatest amount of suckering, but this does not
always occur in practice because factors other than fire severity, such
as parent stand vigor, genetic differences in clones, and competition
with other vegetation also affect postfire sprouting response .
Understory response: Prescribed fire stimulated understory production. Increase in production was still evident 12 years after fire. In 1986, understory production was approximately 2,190 kg/ha on severely burned sites; 2,140 kg/ha on moderately burned sites; and 2,130 kg/ha on sites where fire severity was low. This exceeded prefire production by 42, 46, and 23 percent, respectively .
Smith, Jane Kapler. 1996. Prescribed fire behavior and quaking aspen recovery on Colorado's Front Range. In: Populus tremuloides. 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/ [ ].
Smith, Jane Kapler. 1983. Fire behavior measurements on prescribed burns in four aspen clones of Colorado's Front Range. Fort Collins, CO: Colorado State University. 153 p. Thesis. .
Smith, Jane Kapler. 1996. [Personal communication]. September 14. Missoula, MT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. .
Smith, Jane K.; Laven, Richard D.; Omi, Philip N. 1983. Fire behavior measurements on prescribed burns in aspen clones of Colorado's Front Range. In: Proceedings, 7th conference on fire and forest meteorology; 1983 April 25-28; Fort Collins, CO. [Place of publication unknown]. American Meteorological Society, Society of American Foresters: 58-61. .
Smith, Jane K.; Laven, Richard D.; Omi, Philip N. 1985. Vegetation changes in aspen stands resulting from prescribed burning in recreation areas of the Front Range of Colorado. Final Report. Contract Nos. RM-80-112-GR and RM-81-162-GR (EC-367): Eisenhower Consortium for Western Environmental Forestry Research. 53 p. On file with: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. .
Smith, Jane Kapler; Laven, Richard D.; Omi, Philip N. 1993. Microplot sampling of fire behavior on Populus tremuloides stands in north-central Colorado. International Journal of Wildland Fire. 3(2): 85-94. .
Uneven-aged quaking aspen (Populus tremuloides) clones dominated the stand. Lodgepole pine (Pinus contorta), ponderosa pine (P. ponderosa) and limber pine (P. flexilis) were scattered throughout the stand. [154,155,156]. The understory consisted of large clumps of common juniper (Juniperus communis) interspersed with bearberry (Arctostaphylos uva-ursi) and herbs. Common juniper covered about 20 percent of the study site. Dominant herbaceous species included western yarrow (Achillea millefolium var. occidentalis), bluebell bellflower (Campanula rotundifolia), Virginia strawberry (Fragaria virginiana ssp. virginiana), northern bedstraw (Galium boreale), alpine false springparsley (Pseudocymopterus montanus), dandelion (Taraxacum officinale), pine goldenpea (Thermopsis rhombifolia var. divaricarpa), Kentucky bluegrass (Poa pratensis), and Letterman's needlegrass (Stipa lettermanii) .
Leaf fall had occurred and quaking aspen was dormant.
Elevation at the burn site ranges from 8,910 to 9,075 feet (2,700-2750 m). Topography is gentle with slopes averaging 14 percent. Soils are a shallow, well-drained Red Feather sandy loam underlain by granite bedrock at 10 inches (25 cm). Precipitation varies from 15.2 to 20.9 inches (380-510 mm) per year. Mean annual temperature ranges from 40 to 46 degrees Fahrenheit (4.4-7.8 deg C) [154,156].
Three sites were burned. Site 1 was burned on Oct. 19, 1981, site 2 on Nov. 4, 1981, and site 3 on Nov. 17, 1981. All fires occurred after leaf fall; the second and third were conducted after a light snow had fallen and then melted. Prefire fuel and moisture conditions were :
|Burn site||Understory type||Fuel depth (cm)|
|*21% of woody particles measured were < 0.64 cm diameter; 34% were 0.64-2.54 cm; 31% were 2.55-7.62 cm; 14% were >7.62 cm.|
Because the fire on site 1 spread poorly, strip fires were used. Headfire ignition was used on site 2, and ring-center firing was used on site 3. Weather conditions (median of 9 observations/site) were [180,156]:
|Study site||Burn date||Ignition time (MST)|
|dry bulb (deg C)||relative humidity (%)||wind speed (km/hr)||fuel stick analogs (% dry weight)|
|1||19 Oct||14:35||12||26||4 gusty||10.5|
|2||4 Nov||12:00||13||24||6 steady||10.6|
|3||17 Nov||13:00||17||15||3 steady||9.6|
Fire behavior: The fires burned with low severity except in some common juniper patches. Average fireline intensity was estimated to be 96 kW/m. Very little temperature change was detected below the soil surface; the maximum temperature recorded at the soil surface was 55 degrees C . Less than half of site 1 burned; sites 2 and 3 burned almost completely . Common juniper plots burned more completely than herbaceous plots. Fire behavior on sites 1 and 2 are described in detail (numbers in parentheses are standard deviations) :
|Burn site||Understory type||Area burned (%)||Rate of spread (m/min)||Flame length (cm)||Fuel consumption (kg/sq m)||Total heat release (kcal/sq m)|
|1||herbaceous||32||0.9 (0.8)||13||0.57 (0.48)||2,345 (1,953)|
|1||juniper||----||2.3 (1.7)||86||2.01 (1.03)||8,300 (4,326)|
|2||herbaceous||97||1.6 (1.2)||25||1.19 (0.67)||5,037 (2,640)|
|2||juniper||100||0.4||62||3.34 (0.81)||14,021 (3,420)|
significantly (p=0.0006) longer in common juniper than in herbaceous
fuels. Fuel consumption and total heat release were significantly
(p=0.001) greater in common juniper than herbaceous fuels.
Fuel moisture and availability appeared to control fire spread [180,156]. On common juniper plots, fire removed almost all litter, standing herbs, and common juniper foliage. On herbaceous plots on sites 2 and 3, nearly all fine fuels were consumed by fire. Woody fuels were reduced an average of 18 percent . On many plots, woody fuels were not measurably changed by fire, and on some plots they were increased .
The spring after burning, site 1 showed very light, patchy effects from fire . The authors did not consider this site "effectively burned" and discontinued sampling on it. Fire effects are described for sites 2 and 3: The burns caused about 10 percent mortality in quaking aspen greater than 5 cm dbh in the first postfire year . All quaking aspen originating after the fires were suckers; no seedlings were observed. Sapling (< 5 cm dbh) densities (per hectare) for the year prior to burning and the first postfire year were :
|Age class||Understory type|
|1980||1982||% change||1980||1982||% change|
Sapling densities in unburned areas did not change significantly
(p > 0.05) from the year prior to burning (1980) to the first postfire year
(1982). Changes in sapling densities on burned areas were statistically
significant (p < 0.05). One-year-old saplings increased more than 6,000
percent from 1980 to 1982, while older saplings decreased 87 percent.
Suckering was significantly (p < 0.05) greater in common juniper than
herbaceous plots .
The range of conditions favorable for fall burning in quaking aspen is "vary narrow." The authors recommend burning after leaf fall and before snowfall . In this study, common juniper burned readily but comprised only patches in the understory. If common juniper occurs in the understory and if a patchy burn meets management objectives, the acceptable prescription window may be wider.
Tirmenstein, D. A., compiler. 1989. Prescribed fire in an Arizona quaking aspen/bunchgrass type. In: Populus tremuloides. 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/ [ ].
Covington, W. Wallace; Kurmes, Ernest A.; Haisley, James R. 1983. The effect of controlled burning on understory vegetation and soil nitrogen in the aspen-bunchgrass type. Final report for Research Grant No. RM-80-111-GR (EC-361). Eisenhower Consortium for Western Environmental Forestry Research. 34 p. .
fall (October, 1981)/low
The study site is approximately 20 miles (32 km) northwest of Flagstaff, Arizona, on the Coconino National Forest. The site is between U.S. Highway 180 on the southeast and Kendrick Park to the north, in sections 4, 8, 9, and 18 of Township 23 North and Range 6 East.
The study site was in a quaking aspen (Populus tremuloides)/bunchgrass community. The quaking aspen overstory ranged from 45 to 55 years in age, with tree heights of 36 to 48 feet (11-14.6 m). Average dbh was 6 to 9 inches (16.2-21.6 cm). Some larger, older stems were scattered throughout the site. Understory bunchgrasses included Arizona fescue (Festuca arizonica), mountain muhly (Muhlenbergia montana), and bottlebrush squirreltail (Elymus elymoides). Fringed brome (Bromus ciliatus), sedges (Carex spp.), and mutton grass (Poa fendleriana) were also present. Understory forbs included western yarrow (Achillea millefolium var. occidentalis), lupine (Lupinus spp.), fleabane (Erigeron spp.), American vetch (Vicia americana), dandelion (Taraxacum officinale), and Indian paintbrush (Castilleja spp.).
elevation - 8,033 ft. (2,450 m)
climate - cool and subhumid
mean annual temperature - 43 degrees Fahrenheit (6 deg C)
average January temperature - 25 degrees Fahrenheit (-4 deg C)
average July temperature - 63 degrees Fahrenheit (17 deg C)
average precipitation, July through September - 8 inches (206 mm)
average annual snowfall - 91 inches (2,310 mm)
average growing season - 117 to 160 days
soils - Brolliar stony clay loam of cinder and basaltic parent material
surface soils - moderately fine textured, dark, cobbly, or stony loam
subsoils - reddish brown clay loam or clay
grazing history - rest-rotation allotment in use June 1 through September 30
Backing fires were used first, then short strip headfires were set.
winds - 3 to 6 mph (5-10 km/hr) from the southwest
temperature - 50 to 59 degrees Fahrenheit (10-15 deg C)
flame length - 6 to 12 inches (15-30 cm)
Prefire fuel characteristics:
|Woody fuels(t/ha)||Plot 1||Plot 2||Plot 3||Plot 4|
|Herbaceous fuels (kg/ha)||91.40||370.00||783.00||399.00|
|Moisture content (%)||45||41||36||36|
|Litter depth (cm)||2.30||3.30||2.10||1.10|
|Area burned (%)||61||50||43||10|
Fire was of low intensity and did not kill the quaking aspen overstory. Quaking aspen sprouting increased slightly, but "significantly" (p=0.09), on burn plots compared to control (unburned) plots. By the end of the first postfire growing season, sprout density was 2.1 times the prefire level on burn plots but only 1.7 times the prefire level on control plots. Average sprout densities per hectare on each plot and on all plots combined were:
|Year||Burned sites (SE)||Controls (SE)|
|Plot 1||1981*||200 (231)||200 (231)|
|1982**||1,100 (756)||400 (325)|
|Plot 2||1981||200 (231)||1,600 (1,348)|
|1982||1,200 (1,264)||2,000 (1,424)|
|Plot 3||1981||1,900 (1,192)||200 (231)|
|1982||3,600 (2,956)||400 (326)|
|Plot 4||1981||1,800 (516)||1,800 (516)|
|1982||2,700 (1,740)||2,500 (1,052)|
|Treatment||1,025 (953)||800 (711)|
|Mean||2,150 (1,212)||1,325 (1,087)|
|*1981 values are prefire sprout density means.|
|**1982 values measure postfire sprout density means.|
This fire prescription was ineffective in top-killing the quaking aspen overstory. Sprout production increased slightly on burned plots, but long-term survivorship of sprouts may be poor due to the presence of the quaking aspen overstory. More research is suggested for documentation of the effects of fire in southwestern quaking aspen/bunchgrass communities.
SPECIES: Populus tremuloides
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