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Montana Field Guide

Montana Field Guides

Aspen and Mixed Conifer Forest

Provisional State Rank: S3/S4
* (see reason below)

External Links

State Rank Reason
The system is at risk from aspen decline in general. Shifting climate may reduce range even more.

General Description

This system occurs in north-central Montana in the Big Snowy Mountain range, at elevations of 2,012-2,195 meters (6,600-7,200 feet). Occurrences are typically on gentle to steep slopes on any aspect. Soils in this mountain range are derived from alluvium, colluvium, and residuum from calcareous parent materials. Most current occurrences represent a late-seral stage of aspen (Populus tremuloides) forest changing to a pure conifer forest. Nearly a hundred years of fire suppression and livestock grazing have converted much of the pure aspen occurrences to the present-day aspen-conifer forest and woodland ecological system, with conifers increasing in dominance. Conifers in this system include Douglas-fir (Pseudotsuga menziesii), subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii) and lodgepole pine (Pinus contorta). Common shrubs include serviceberry (Amelanchier alnifolia), creeping Oregon grape (Mahonia repens), chokecherry (Prunus virginiana), Woods’ rose (Rosa woodsii), birch-leaf spiraea (Spiraea betulifolia), and snowberry (Symphoricarpos species).

Diagnostic Characteristics
Forest and Woodland, Aspen and Conifer mixed forest, montane elevation, side and toe slope topography

Similar Systems

This system occurs in north-central Montana in the Big Snowy Mountain range, at elevations of 2,012-2,195 meters (6,600-7,200 feet) on gentle to steep mountain slopes.

Ecological System Distribution
Approximately 200 square kilometers are classified as Aspen and Mixed Conifer Forest 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, Carter, 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, Powder River, Powell, Ravalli, Sanders, Silver Bow, Stillwater, Sweet Grass, Teton, Wheatland

Spatial Pattern

In Montana, this system is found on montane slopes, where climate is dry and cold during winter months. Most precipitation occurs during late spring and early summer months. Distribution is primarily limited to areas of deeper soils with adequate soil moisture. Occurrences at high elevations are restricted by cold temperatures, and are generally only found on warmer southern aspects. By contrast, at lower elevations, aspen is restricted by lack of moisture and is found on cooler north aspects and mesic microsites. Soils are typically deep and well-developed, with rock often absent from the soil. Soil texture ranges from sandy loam to clay loam.


The tree canopy is composed of a mix of deciduous and coniferous species, co-dominated by aspen (Populus tremuloides) and conifers, including Douglas-fir (Pseudotsuga menziesii), subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta) and ponderosa pine (Pinus ponderosa). Common understory shrubs include serviceberry (Amelanchier alnifolia), creeping Oregon grape (Mahonia repens), chokecherry (Prunus virginiana), Woods’ rose (Rosa woodsii), birch-leaf spiraea (Spiraea betulifolia), and snowberry (Symphoricarpos species). Graminoid composition varies depending on available site moisture, but often includes mountain brome (Bromus carinatus), pinegrass (Calamagrostis rubescens), Geyer’s sedge (Carex geyeri), blue wild rye (Elymus glaucus), and needlegrasses (Achnatherum and Nassella species). Common forbs include yarrow (Achillea millefolium), heart-leafarnica (Arnica cordifolia), aspen daisy (Erigeron speciosus), northern bedstraw (Galium boreale), silver lupine (Lupinus argenteus), starry Solomon’s seal (Maianthemum stellatum), and meadow rue (Thalictrum species). Exotic species such as Kentucky bluegrass (Poa pratensis), timothy (Phleum pratense) and common dandelion (Taraxacum officinale) are frequentin areas impacted 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
A0540 Pinus flexilis Rocky Mountain Woodland Alliance
A3395 Pseudotsuga menziesii - Pinus ponderosa / Herbaceous Understory Central Rocky Mountain Woodland Alliance
A3398 Pinus ponderosa Southern Rocky Mountain Forest & Woodland Alliance
A3454 Pseudotsuga menziesii Southern Rocky Mountain Forest & Woodland Alliance
A3462 Pseudotsuga menziesii Middle Rocky Mountain Dry-Mesic Forest & Woodland Alliance
A3463 Pseudotsuga menziesii Middle Rocky Mountain Mesic-Wet Forest Alliance
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

Quaking aspen is seral in this system, and in the absence of fire or other disturbance the system will succeed to conifer-dominated forest (Mueggler, 1988). Succession by conifers may occur as a result of a number of processes. Soils may become more acidic and less nutrient-rich as aspen decline in the absence of disturbance, favoring conifer establishment (Cryer and Murray, 1992). Aspen may also facilitate the establishment of conifers due to the shade and higher soil moisture at the base of aspen trees, fostering interspecific competition that favor conifer dominance (St. Clair et al., 2013). Conifer establishment and growth has been found to be greater in aspen and mixed-conifer stands than in conifer dominated stands due to greater nutrient, light, and water availability. Alternatively, aspen mortality tends to increase with increasing conifer abundance due to aspen’s shade-intolerance, and changes to soil chemistry (St. Clair et al., 2013). Light limitation resulting from conifer dominance additionally reduces defense compounds in aspen leaves increasing their susceptibility to herbivory (Wooley et al., 2008).

Fire return intervals in this system generally range from 30-50 years and are mostly either mixed severity or stand-replacing (U.S. Department of Agriculture, 2012). Young conifers are susceptible to fire, but older individuals can withstand low-intensity ground fires. While easily killed by fire, aspen regenerate quickly and will often dominate immediately after fires in this system (Howard, 1996). Shinneman et al., (2013) describe two types of seral mixed aspen-conifer forest types: Montane stands where fire is adequately frequent and severe to allow aspen to persist where conifer competitors are present, and mesic subalpine stands where infrequent, high severity fires promote a short period of aspen dominance before it is replaced by more shade-tolerant conifers. In part due to fire suppression practices since the early 1900s, conifers have become dominant in many seral aspen stands (Howard, 1996).

In Montana, aspen seed production is erratic and infrequent. Natural seedling establishment is rare due to limited years of viable seed dispersal, and the long, moist conditions required for initial germination and first-year establishment. Drought conditions limit natural regeneration, and also may accelerate succession as conifer species are generally more tolerant of drought. Thus, conifers are more likely to persist in this system as drought severity and frequency increase (Bell et al., 2014; St. Clair et al., 2013). Conifers may be additionally favored in stands where heavy use by livestock and wildlife limit aspen regrowth, as conifer species are generally more tolerant of browsing. Conversely, increasingly frequent fires will likely cause conifer mortality and promote aspen regeneration (St. Clair et al., 2013).


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 during late fall months to maintain and enhance aspen regeneration and limit succession by conifers (Hardy and Arno, 1996). 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). Maintaining fire regimes in combination with the management of ungulate use can slow mortality related to succession by conifers, and increase aspen resilience to drought by limiting competition for water with adjacent conifers (St. Clair et al., 2013).

Restoration Considerations
Restoration strategies for this system will depend largely on the severity of the fire, grazing intensity, and other land use impacts. Maintenance of historic fire regimes is the primary method recommended for restoring this system (St. Clair et al., 2013). Quaking 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. Because burned areas regenerate vegetatively following fire, additional restoration practices are generally not required. When supplemental planting is necessitated, seedlings are recommended over 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, and by re-sprouting of dominant shrubs. 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 this system may be additionally desired as changes in species composition that occur with succession result in changes to ecosystem productivity, nutrient cycling, and may result in changes to watershed-wide water quality (St. Clair et al., 2013; 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
K.A. Schulz, mod. M.S. Reid and G. Kittel

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

Version Date

  • Classification and Map Identifiers

    Cowardin Wetland Classification: Not applicable

    NatureServe Identifiers:
    Element Global ID
    System Code CES304.776, Inter-Mountain Basins Aspen Mixed Conifer Forest-Woodland

    National Land Cover Dataset:
    43: Mixed Forest

    4302: Inter-Mountain Basins Aspen Mixed Conifer Forest-Woodland

  • Literature Cited AboveLegend:   View Online Publication
    • 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.
    • Cryer, D.H. and J.E. Murray. 1992. Aspen regeneration and soils. Rangelands Archives 14(4):223-226.
    • 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.
    • 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.
    • 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.
    • St. Clair, S.B., X. Cavard, and Y. Bergeron. 2013. The role of facilitation and competition in the development and resilience of aspen forests. Forest ecology and management 299:91-99.
    • 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
    • Wooley, S.C., S. Walker, J. Vernon, and R.L. Lindroth. 2008. Aspen Decline, Aspen Chemistry, and Elk Herbivory: Are They Linked? Aspen chemical ecology can inform the discussion of aspen decline in the West. Rangelands 30(1):17-21.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Hardy, Colin C., and Stephen F. Arno. 1996. The use of fire in forest restoration a general session at the annual meeting of the Society for Ecological Restoration : Seattle, WA, September 14-16, 1995. Ogden, Utah (324 25th Street, Ogden 84401): U.S. Dept. of Agriculture, Forest Service, Intermountain Research Station.

    • 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.
    • 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.

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Citation for data on this website:
Aspen and Mixed Conifer Forest — Inter-Mountain Basins Aspen Mixed Conifer Forest-Woodland.  Montana Field Guide.  Retrieved on , from