Rocky Mountain Aspen Forest and Woodland
Global Name:
Rocky Mountain-Interior Subalpine-Montane Aspen Forest
Global Rank:
G4G5
State Rank:
S3S4
(see reason below)
External Links
State Rank Reason
Aspen stands are widespread in mountainous areas and are common in some geographic areas though much more limited in size and extent in others. Stands have generally decreased in extent and condition and continue to be threatened primarily by invasive species, especially non-native grasses, by changes in fire frequency and related conifer encroachment and from stress related to drought and climate change.
General Description
This National Vegetation Classification Group is dominated by Quaking Aspen and it occurs on both sides of the Continental Divide but is more common east of the Divide. It occurs in the montane and subalpine zones throughout much of Montana. Elevations range from approx 3,000ft in northwest Montana to 8,000ft in southwest Montana with stands mostly between 4,500-7,000ft. Stands are dominated by Quaking Aspen (Populus tremuloides) or in limited areas of northwest Montana by Paper Birch (Betula papyrifera). Stands of aspen in Montana are generally relatively small in extent but occasionally form large patches. Sites within this group are upland sites and do not include riparian or wetlands sites that are dominated by aspen or birch, nor aspen communities on the Great Plains. Distribution of this group is primarily limited to areas with relatively high soil moisture and occurs on gentle to moderate slopes, in swales, or on level sites. At lower elevations, occurrences are found on cooler, north aspects and mesic sites. Stands can be stable and long-lived or seral to Douglas-fir (Pseudotsuga menziesii), Subalpine Fir (Abies lasiocarpa) or Engelmann Spruce (Picea engelmannii, Picea x albertiana) dominated forests (Habeck 1967, Pfister et al, 1977). In this group, conifers that may be present, forming up to 25% of the tree canopy but are never codominant. The understory structure may be complex with multiple shrub and herbaceous layers, or simple, with just an herbaceous layer. The herbaceous layer may be dense or sparse, dominated by mesic grasses or forbs. Occurrences of this group often originate, and are likely maintained, by stand-replacing disturbances such as crown fire, disease, windthrow, elk and beaver activity.
Aspen stands within riparian or wetland sites are part of either G505 Montane Forested Wetland or G506 Montane - Subalpine Riparian Forest. Aspen stands in the Great Plains Region not including stands within the island ranges are often part of G328 Great Plains Aspen Forest & Woodland.
This group encompasses the Aspen Forest and Woodland Ecological System and a portion of the Aspen and Mixed Conifer Forest Ecological System.
Diagnostic Characteristics
Quaking Aspen (Populus tremuloides) or Paper Birch (Betula papyrifera) in limited areas of northwest Montana; Montane and Foothills Zones; Deciduous Forest and Woodlands.
Similar Systems
Range
In Montana, this group is found throughout the mountainous portion of the state on both sides of the Continental Divide, including in the island ranges of central Montana. It is most common in areas such as along and within the mountains of the Rocky Mountain Front and in the island ranges such as the Highwoods and the Little Belt Mountains. It is extensive along portions of the Rocky Mountain Front where it grades into G328 Great Plains Aspen Forest & Woodland.
In MT, G222 occurs within these Level III Ecoregions: 15 (Northern Rockies), 16 (Idaho Batholith), 17 (Middle Rockies) and 41 (Canadian Rockies).
In Montana, G222 occurs within these Major Land Resource Areas: 43A-Northern Rocky Mountains; 43B-Central Rocky Mountains and 46 - Northern and Central Rocky Mountain Foothills.
Density and Distribution
Based on 2025 land cover layer. Grid on map is based on USGS 7.5 minute quadrangle map boundaries.
Mapped Distribution by County
Beaverhead, Big Horn, Blaine, Broadwater, Carbon, Cascade, Chouteau, Deer Lodge, Fergus, Flathead, Gallatin, Glacier, Golden Valley, Granite, Hill, Jefferson, Judith Basin, Lake, Lewis and Clark, Liberty, Lincoln, Madison, Meagher, Mineral, Missoula, Park, Phillips, Pondera, Powell, Ravalli, Sanders, Silver Bow, Stillwater, Sweet Grass, Teton, Toole, Wheatland
Based on 2025 land cover layer.
Spatial Pattern
Large Patch
Environment
Aspen stands in this group occur in the montane and subalpine zones. Elevations range from approx 3,000ft in northwest Montana to 8,000ft in southwest Montana with stands mostly between 4,500-7,000ft. Climate is temperate with a relatively long growing season, typically cold winters and deep snow. Mean annual precipitation is greater than 15 inches and typically greater than 20 inches, except in semi-arid environments where occurrences are restricted to mesic, microsites such as seeps or areas below large snow drifts. Stands can occur on gentle to moderate slopes, in swales, or on level sites. At lower elevations, occurrences are found on cooler, north aspects and mesic sites. Soils are usually deep and well developed, with rock often absent from the soil. Soil texture ranges from sandy loam to clay loams. In Glacier County, aspens stands differ in height growth, which is controlled by recurring Chinook winds.
Vegetation
This group includes Quaking Aspen stands with a relatively closed canopy of trees 5-20 meters (16 to 66 feet) tall. In Montana, most aspen clones are smaller than in the Central Rocky Mountain Region to the south. Clones can be stable and long-lived or seral to Douglas-fir (Pseudotsuga menziesii), Subalpine Fir (Abies lasiocarpa) or Engelmann Spruce (Picea engelmannii, Picea x albertiana) dominated forests (Habeck 1967, Pfister et al 1977). Stands of Paper Birch (Betula papyrifera) in upland setting also occur within this group. These are restricted primarily to northwest Montana and are very minor in extent and abundance.
Depending on available soil moisture and other factors like disturbance, the understory structure may be complex with multiple shrub and herbaceous layers, or simple with just an herbaceous layer. The herbaceous layer may be dense or sparse, dominated by graminoids or forbs. Common shrubs include Rocky Mountain Maple (Acer glabrum), Serviceberry (Amelanchier alnifolia), Sreeping Oregon-grape (Berberis repens), Chokecherry (Prunus virginiana), Rose (Rosa spp.), Thimbleberry (Rubus parviflorus), and Snowberry (Symphoricarpos spp.). The herbaceous layers may be lush and diverse. Common graminoids may include Mountain Brome (Bromus carinatus), Pinegrass (Calamagrostis rubescens), Ross’ Sedge (Carex rossii), Blue Wildrye (Elymus glaucus), Slender Wheatgrass (Elymus trachycaulus) and Bearded Fescue (Festuca subulata). Common mesic understory forbs include Yarrow (Achillea millefolium), Angelica arguta, Engelmann Aster (Eucephalus engelmannii), Larkspur (Delphinium species), Fleabane (Erigeron speciosus), Richardson’s Geranium (Geranium richardsonii), Cow-parsnip (Heracleum maximum), Western Sweet-cicely (Osmorhiza occidentalis), Western meadowrue (Thalictrum occidentale), Stinging Nettle (Urtica dioica) and Small-flower Valerian (Valeriana occidentalis). Bracken fern (Pteridium aquilinum) is present in some stands. Exotic grasses such as Kentucky Bluegrass (Poa pratensis), Common Timothy (Phleum pratense) and Smooth Brome (Bromus inermis) are often common in occurrences disturbed by grazing.
In Montana, this group is currently represented by 6 Alliances and 20 Associations within the National Vegetation Classification. These likely represent the diversity of types found within the state.
National Vegetation Classification
Download the complete NVC hierarchy for Montana
TT2 B02 Temperate-Boreal Forest and Woodland
TT2.b S92 Cool Temperate Forest and Woodland
TT2.b3 F112 Temperate Continental Conifer Forest and Woodland
TT2.b3.Nd D336 Western Cordilleran Subalpine-High Montane Forest and Woodland
TT2.b3.Nd.2 M020 Rocky Mountain Subalpine-Upper Montane Forest and Woodland
TT2.b3.Nd.2.d G222 Rocky Mountain-Interior Subalpine-Montane Aspen Forest
A2312 Populus tremuloides Tall Shrub Rocky Mountain Forest Alliance
CEGL000564 Populus tremuloides / Amelanchier alnifolia Forest
CEGL000567 Populus tremuloides / Amelanchier alnifolia - Symphoricarpos oreophilus / Calamagrostis rubescens Forest
CEGL000596 Populus tremuloides / Prunus virginiana Forest
A2313 Populus tremuloides Short Shrub Rocky Mountain Forest Alliance
CEGL000602 Populus tremuloides / Rubus parviflorus Forest
CEGL000607 Populus tremuloides / Spiraea betulifolia Forest
CEGL000610 Populus tremuloides / Symphoricarpos oreophilus Forest
CEGL000945 Populus tremuloides / Physocarpus malvaceus - Amelanchier alnifolia Scree Woodland
A2315 Populus tremuloides Moist-Mesic Herbaceous Rocky Mountain Forest Alliance
CEGL000586 Populus tremuloides / Heracleum sphondylium Forest
CEGL000595 Populus tremuloides / Heracleum maximum Forest
CEGL000618 Populus tremuloides / Tall Forbs Forest
CEGL000619 Populus tremuloides / Thalictrum fendleri Forest
CEGL005849 Populus tremuloides / Urtica dioica Forest
A2316 Populus tremuloides / Grass Understory Rocky Mountain Forest Alliance
CEGL000573 Populus tremuloides / Bromus carinatus Forest
CEGL000575 Populus tremuloides / Calamagrostis rubescens Forest
CEGL000579 Populus tremuloides / Carex geyeri Forest
CEGL003748 Populus tremuloides / Invasive Perennial Grasses Forest
A2317 Populus tremuloides / Dwarf-shrub Rocky Mountain Forest Alliance
CEGL000587 Populus tremuloides / Juniperus communis Forest
CEGL000594 Populus tremuloides / Mahonia repens Forest
A3367 Betula papyrifera Rocky Mountain Forest and Woodland Alliance
CEGL000520 Betula papyrifera Forest
CEGL005844 Betula papyrifera / Acer glabrum Woodland
*Disclaimer: Some Alliances and Associations are considered provisional. Some require further documentation to verify their occurrence in the state
and some may be modified or deleted in future revisions after collection of additional data and information.
Dynamic Processes
Stands often originate with, and are likely maintained by, stand-replacing disturbances such as crown fire, disease and windthrow, or logging by humans or beaver. Fire return intervals vary from approximately 30-165 years and range from mixed severity to stand replacing (U.S. Department of Agriculture 2012). In general, aspen stands are relatively resistant to fire due to high fuel moisture content, however, favorable fire weather conditions can result in the spread of fire within aspen stands (Shinneman etal. 2013). Stems are killed by ground fires but can quickly and vigorously resprout by root suckers in high densities (Howard 1996). Stems are relatively short-lived (70-120 years), and the group will generally succeed to longer-lived, shade-tolerant conifer forest if undisturbed, although seemingly stable fire-independent stands appear to also exist where edaphic and topographic conditions favor the dominance of aspen over conifers (Shinneman et al. 2013). Occurrences are often favored by fire in the conifer zone (Mueggler, 1988).
In Montana, seed production is erratic and infrequent. Natural seedling establishment is limited to years of viable seed production. Seedling recruitment is limited to sites where there is adequate soil moisture following dispersal in early summer. Following the Yellowstone fires of 1988, quaking aspen seedlings established on many suitable sites, however, re-sprouting was greater in stands that had burned (Romme et al. 1995), and seedlings were found only in burned forests (Turner et al. 2003). These seedling and sapling stands are subjected to heavy elk browsing and may not reach full maturity (Hessl and Graumlich 2002).
Quaking aspen is dioecious; clones are either male or female. Reproduction is largely clonal. Some clones are thought to be centuries old and have the potential to be large in size. Stems are produced from a common root system; new stems are produced on the outer edge, advancing in front of the clone, with older trees in the center. The root system persists as stems die and are replaced. Clones can be distinguished by morphological differences in flowering and leaf emergence phenology, leaf size and shape, branching habit, stem character, and gender. Quaking aspen reproduces vegetatively by sprouting from stumps and root crowns, and by forming suckers (adventitious shoots on roots). The ability of aspen to regenerate by suckers can vary widely among clones (Schier et al, 1985) and suckering response may increase with fire severity (Keyser et al., 2005).
In recent years, many aspen stands have exhibited mortality from biotic vectors. Some examples include Cytospora canker which is not highly destructive in healthy trees, and bronze poplar borer (Agrilus liragus) (Marchetti et al. 2011). These pathogens infect and proliferate in aspen stands already stressed by drought, insects, past fires, wind damage and heavy livestock and wildlife use (Shinneman et al. 2013; Marchetti et al. 2011). In addition to the tendency of drought to increase susceptibility to attack by biotic vectors, drought-related damage may also increase aspen vulnerability to future droughts (Anderegg et al., 2013). Large, older trees are generally more sensitive to water stress (Bell et al. 2014), making stands with low levels of regeneration particularly susceptible to drought-related mortality.
Management
Historic fire suppression combined with excessive browsing of young aspen by ungulates is a primary cause of aspen decline in the Northern Rockies (Shinneman et al. 2013). In the absence of natural fire, periodic prescribed burns can be implemented to maintain and enhance regeneration in declining stands with low productivity. The best conditions for burning generally occur in the early spring or late fall when surface fuels are dry and frozen when aspen stands are more vulnerable (Howard, 1996). Brown and Simmerman (1986) describe methods for determining appropriate timing of prescribed burning in aspen stands. Aspen will typically reproduce prolifically post-burning, however in areas where livestock or wildlife browsing is severe, ungulate management to reduce damage to new growth may be necessary (Shinneman et al. 2013; Durham and Marlow 2010). A study in southwestern Montana found that aspen regeneration increased after prescribed burning, and that ungulate browsing did not limit regeneration due to the low elk density and management of cattle grazing in this region (Durham and Marlow 2010).
Restoration Considerations
Restoration strategies will depend on fire severity, grazing or other land impacts. Because burned areas regenerate vegetatively following fire, additional restoration practices are generally not required. When supplemental planting is necessitated, seedlings preferable to vegetative cuttings, and seed germination and seedling survival are highest on well-drained, moist mineral seedbeds (Howard 1996). Early successional stages may be dominated by fireweed (Chamerion angustifolium) and other forbs, small amounts of forest graminoids such as mountain brome, blue wildrye, and pinegrass, and by re-sprouting of dominant shrubs. Aspen will resprout vigorously following fires of low to moderate severity. Sprouting will also occur after higher intensity fires from root suckers that are deeper in the soil profile. In areas with high elk densities or heavy livestock use, aspen regeneration may require protection from browsing until crowns can grow high enough to avoid excessive browsing damage (6-8 years) (Durham and Marlow 2010; Howard 1996). Restoration of aspen stands may be additionally valuable as the species is unique in its ability to stabilize soil and protect watershed-wide water quality (Howard 1996).
Species Associated with this Community
- How Lists Were Created and Suggested Uses and Limitations
Animal Species Associations
Please note that while all vertebrate species have been systematically associated with vegetation communities, only a handful of invertebrate species have been associated with vegetation communities and invertebrates lists for each vegetation community should be regarded as incomplete. Animal species associations with natural vegetation communities that they regularly breed or overwinter in or migrate through were made by:
- Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Werner et al. 2004, Adams 2003, and Foresman 2012);
- Evaluating structural characteristics and distribution of each vegetation community relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each vegetation community;
- Calculating the percentage of observations associated with each vegetation community relative to the percent of Montana covered by each vegetation community to get a measure of "observations versus availability of habitat".
Species that breed in Montana were only evaluated for breeding habitat use. Species that only overwinter in Montana were only evaluated for overwintering habitat use. Species that only migrate through Montana were only evaluated for migratory habitat use. In general, species are listed as associated with a vegetation community if it contains structural characteristics known to be used by the species. However, species are not listed as associated with a vegetation community if we found no support in the literature for the species’ use of structural characteristics of the community even if point observations were associated with it. If you have any questions or comments on animal species associations with vegetation communities, please contact the Montana Natural Heritage Program's Senior Zoologist.
Plant Species Associations
Please note that while diagnostic, dominant, or codominant vascular plant species for a vegetation community have been systematically assigned to those communities and vascular plant Species of Concern were systematically evaluated for their associations with vegetation communities, the majority of Montana’s vascular plant species have not been evaluated for their associations with vegetation communities and no attempt has been made to associate non-vascular plants, fungi, or lichens with vegetation communities. Plant species associations with natural vegetation communities were made in a manner similar to that described above for animals, but with review of Lesica et al. (2022) and specimen collection data from the Consortium of Pacific Northwest Herbaria. If you have any questions or comments on plant species associations with vegetation communities, please contact the Montana Natural Heritage Program's Program Botanist.
Suggested Uses and Limitations
Species associations with vegetation communities should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning. These potential lists of species should not be used in place of documented occurrences of species or predicted habitat suitability models (this information can be requested at: https://mtnhp.mt.gov/requests/), or systematic surveys for species and onsite evaluations of habitat by trained biologists. Users of this information should be aware that the land cover data used to generate species associations is based on satellite imagery from 2016 and was only intended to be used at broader landscape scales. Land cover mapping accuracy is particularly problematic when the vegetation communities occur as small patches or where the land cover types have been altered over the past decade. Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections). Finally, although a species may be associated with a particular vegetation community within its known geographic range, portions of that vegetation community may occur outside of the species' known geographic range.
Literature Cited
- Adams, R.A. 2003. Bats of the Rocky Mountain West; natural history, ecology, and conservation. Boulder, CO: University Press of Colorado. 289 p.
- Consortium of Pacific Northwest Herbaria. https://www.pnwherbaria.org/ Last accessed May 30, 2025.
- Dobkin, D. S. 1992. Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34. Missoula, MT.
- Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
- Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998. Montana atlas of terrestrial vertebrates. Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT. 1302 p.
- Hutto, R.L. and J.S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32. 72 p.
- Lesica P., M. Lavin, and P.F. Stickney. 2022. Manual of vascular plants, 2nd Edition. Brit Press. 779 p.
- Maxell, B.A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to U.S. Forest Service Region 1. Missoula, MT: Wildlife Biology Program, University of Montana. 161 p.
- Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath. 2004. Amphibians and reptiles of Montana. Missoula, MT: Mountain Press Publishing Company. 262 p.
- Species of Concern Associated with this Community
Vascular Plants
Mammals
Birds
Amphibians
Invertebrates
- Diagnostic, Dominant, or Codominant Plant Species for this Community
Vascular Plants
Original Concept Authors
M.E. Hall; F.H. Eyre (1980)
Montana Version Authors
S. Mincemoyer
Version Date
11/25/2024
References
- Literature Cited AboveLegend:
View Online Publication
Anderegg, W.R., L. Plavcová, L.D. Anderegg, U.G. Hacke, J.A. Berry, and C.B. Field. 2013. Drought's legacy: multiyear hydraulic deterioration underlies widespread aspen forest die-off and portends increased future risk. Global Change Biology 19(4):1188-1196.- Bell, D.M., J.B. Bradford, and W.K. Lauenroth. 2014. Forest stand structure, productivity, and age mediate climatic effects on aspen decline. Ecology 95(8):2040-2046.
- Brown, J.K. and D.G.Simmerman. 1986. Appraising fuels and flammability in western aspen: a prescribed fire guide. Gen. Tech. Rep. INT-205. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 48 p.
- Durham, D.A. and C.B. Marlow. 2010. Aspen response to prescribed fire under managed cattle grazing and low elk densities in southwest Montana. Northwest Science 84(1):141-150.
- Habeck, J. R. 1967. The vegetation of northwestern Montana: A preliminary report. Department of Botany, University of Montana, Missoula. 57 pp.
- Hessl, A.E. and L.J. Graumlich. 2002. Interactive effects of human activities, herbivory and fire on quaking aspen (Populus tremuloides) age structures in western Wyoming. Journal of Biogeography 29(7):889-902.
- Howard, J.L. 1996. Populus tremuloides. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
- Keyser, T.L., F.W. Smith, and W.D. Shepperd. 2005. Trembling aspen response to a mixed-severity wildfire in the Black Hills, South Dakota, USA. Canadian Journal of Forest Research 35(11):2679-2684.
- Marchetti, S.B., J.J. Worrall, and T. Eager. 2011. Secondary insects and diseases contribute to sudden aspen decline in southwestern Colorado, USA. Canadian Journal of Forest Research 41(12):2315-2325.
- Mueggler, W. F. 1988. Aspen community types of the Intermountain Region. USDA Forest Service General Technical Report INT-250. Intermountain Research Station, Ogden, UT. 135 pp.
- Pfister, R. D., B. L. Kovalchik, S. F. Arno, and R. C. Presby. 1977. Forest habitat types of Montana. USDA Forest Service. General Technical Report INT-34. Intermountain Forest and Range Experiment Station, Ogden, UT. 174 pp.
- Romme, W.H., M.G. Turner, L.L. Wallace, and J.S. Walker. 1995. Aspen, elk, and fire in northern Yellowstone Park. Ecology 76(7):2097-2106.
- Schier GA, Jones JR, Winokur RP. 1985. Vegetative regeneration. In: DeByle NV, Winokur RP, editors. Aspen: ecology and management in the western United States. USDA Forest Service General Technical Report RM-119. Fort Collins, CO: Rocky Mountain Forest and Range Experiment Station; p 29-33.
- Shinneman, D.J., W.L. Baker, P.C. Rogers, and D. Kulakowski. 2013. Fire regimes of quaking aspen in the Mountain West. Forest Ecology and Management 299: 22-34.
- Turner, M.G., W.H. Romme, R.A. Reed, and G.A. Tuskan. 2003. Post-fire aspen seedling recruitment across the Yellowstone (USA) landscape. Landscape Ecology 18(2):127-140.
- U.S. Department of Agriculture, Forest Service, Missoula Fire Sciences Laboratory. 2012. Information from LANDFIRE on Fire Regimes of Northern Rocky Mounatin Quaking Aspen Communities. In: Fire Effects Information System, [Online]. U.S. Department of Agri
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