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Montana Field Guide

Montana Field Guides

Aspen Forest and Woodland

Provisional State Rank: S3

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General Description

This widespread ecological system is more common in the southern and central Rocky Mountains, but occurs in the montane and subalpine zones throughout much of Montana north into Canada. It is similar to the Inter-Mountain Basins Aspen Mixed Conifer Forest-Woodland found in the Big Snowy Mountains, but lacks the conifer component. Distribution of this system is primarily limited by adequate soil moisture required to meet its high evapotranspirative demand, length of growing season, and temperatures. Mean annual precipitation where these systems occur is generally greater than 38 centimeters (15 inches) and typically greater than 51 centimeters (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. This system describes mesic forests and woodlands dominated by quaking aspen (Populus tremuloides) without a significant conifer component (<25% relative tree cover). This aspen system can be stable and long-lived with little encroachment of coniferous species. 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 system often originate, and are likely maintained, by stand-replacing disturbances such as crown fire, disease, windthrow, elk and beaver activity.

Diagnostic Characteristics
Northwestern Great Plains Aspen Forest and Parkland and Inter-Mountain Basins Aspen-Mixed Conifer Forest & Woodland

Similar Systems

In Montana, this system is found throughout the Rocky Mountains and island ranges of eastern and south-central Montana. Elevations generally range from 1,493 to 2,743 meters (4,900-9,000 + feet), but occurrences can be found at lower elevations in some regions.

Ecological System Distribution
Approximately 1,699 square kilometers are classified as Aspen Forest and Woodland in the 2016 Montana Land Cover layers.  Grid on map is based on USGS 7.5 minute quadrangle map boundaries.

Montana Counties of Occurrence
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, Lincoln, Madison, Meagher, Mineral, Missoula, Park, Phillips, Pondera, Powell, Ravalli, Sanders, Silver Bow, Stillwater, Sweet Grass, Teton, Wheatland

Spatial Pattern
Large patch and Small patch

Climate is temperate with a relatively long growing season, typically cold winters and deep snow. Mean annual precipitation is greater than 38 centimeters (15 inches) and typically greater than 51 centimaters (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.


This system includes 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 region. Clones can be stable and long-lived or seral to Douglas-fir (Pseudotsuga menziesii), subalpine fir (Abies lasiocarpa) or spruce (Picea species) dominated forests (Habeck, 1967). Stable climax aspen forest also occurs in southwestern Montana (Pfister et al, 1977). Conifers that may be present but are never codominant include subalpine fir, Engelmann spruce (Picea engelmannii), white spruce (Picea glauca), ponderosa pine (Pinus ponderosa), and Douglas-fir. Conifer species may contribute up to 25% of the tree canopy before the occurrence is reclassified as a mixed occurrence. This system can be interpreted in some instances to be the seral phase of the Inter-Mountain Basins Aspen-Mixed Conifer Forest & Woodland. In Glacier County, this system differs in height growth, which is controlled by recurring Chinook winds.

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), creeping Oregon grape (Mahonia 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), sharptooth angelica (Angelica arguta), Engelmann aster (Eucephalus engelmannii),larkspur (Delphinium species), aspen daisy (Erigeron speciosus), Richardson’s geranium (Geranium richardsonii), common cow parsnip (Heracleum maximum), western sweet cicely (Osmorhiza occidentalis), western meadow rue (Thalictrum occidentale), stinging nettle (Urtica dioica) and western valerian (Valeriana occidentalis). Bracken fern (Pteridium aquilinum) is present in some stands.Exotic grasses such as the perennials Kentucky bluegrass (Poa pratensis), common timothy (Phleum pratense) and smooth brome (Bromus inermis) are often common in occurrences disturbed by grazing.

National Vegetation Classification Switch to Full NVC View

Adapted from US National Vegetation Classification

A0422 Abies lasiocarpa - Populus tremuloides Rocky Mountain Moist Forest Alliance
CEGL005911 Populus tremuloides / Conifer - Spiraea betulifolia / Symphoricarpos albus Forest
A2036 Populus tremuloides Rocky Mountain Forest & Woodland Alliance
CEGL000564 Populus tremuloides - Amelanchier alnifolia Forest
CEGL000567 Populus tremuloides - Amelanchier alnifolia / Symphoricarpos oreophilus - Calamagrostis rubescens Forest
CEGL000573 Populus tremuloides - Bromus carinatus Forest
CEGL000575 Populus tremuloides - Calamagrostis rubescens Forest
CEGL000579 Populus tremuloides - Carex geyeri Forest
CEGL000586 Populus tremuloides - Heracleum sphondylium Forest
CEGL000587 Populus tremuloides - Juniperus communis Forest
CEGL000594 Populus tremuloides - Mahonia repens Forest
CEGL000595 Populus tremuloides - Heracleum maximum Forest
CEGL000602 Populus tremuloides - Rubus parviflorus Forest
CEGL000607 Populus tremuloides - Spiraea betulifolia Forest
CEGL000609 Populus tremuloides - Symphoricarpos albus Forest
CEGL000610 Populus tremuloides - Symphoricarpos oreophilus Forest
CEGL000618 Populus tremuloides - Tall Forbs Forest
CEGL000619 Populus tremuloides - Thalictrum fendleri Forest
CEGL003748 Populus tremuloides - Invasive Perennial Grasses Forest
CEGL005849 Populus tremuloides - Urtica dioica Forest
A3465 Pinus ponderosa Mesic Black Hills Forest Alliance
CEGL000596 Populus tremuloides - Prunus virginiana Forest
A3760 Populus tremuloides Riparian Forest Alliance
*Disclaimer: Alliances and Associations have not yet been finalized in the National Vegetation Classification (NVC) standard.  A complete version of the NVC for Montana can be found here.

Dynamic Processes

Occurrences of this ecological system 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). The diversity of fire regimes is attributable to the variability of stand structure, topography, and climate found within this system (Shinneman et al., 2013). 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 stands (Shinneman et al., 2013). Boles 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 system 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 outside, 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, bole 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.

Historic fire suppression combined with excessive browsing of young aspen by ungulates is considered to be 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 Ecological System
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. 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, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system 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, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems 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 (this information can be requested at: or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems 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 ecological system within its known geographic range, portions of that ecological system 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.
    • 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.
    • 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.

Original Concept Authors
M.S. Reid, mod. G. Kittel

Montana Version Authors
L.K. Vance, T. Luna, M.M. Hart

Version Date

  • Classification and Map Identifiers

    Cowardin Wetland Classification: Not applicable

    NatureServe Identifiers:
    Element Global ID 28649
    System Code CES306.813, Rocky Mountain Aspen Forest and Woodland

    National Land Cover Dataset:
    41: Deciduous Forest

    4104: Rocky Mountain Aspen Forest and Woodland

  • 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.
    • 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.
    • 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.
    • 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
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • 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.
    • 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.
    • Sisson, L. 1976. The sharp-tailed grouse in Nebraska. Neb. Game and Parks Comm. Lincoln. 87 pp.

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Citation for data on this website:
Aspen Forest and Woodland — Rocky Mountain Aspen Forest and Woodland.  Montana Field Guide.  Retrieved on , from