Rocky Mountain Subalpine Woodland and Parkland
Provisional State Rank
(see reason below)
State Rank Reason
Blister rust, insects and drought are all affecting these forests. Although decline has not been as widespread as with some other ecological systems, it is expected to continue, especially if winters are mild.
This system includes all subalpine and treeline forest associations of the Montana Rocky Mountains and island ranges. It is characteristically a high-elevation mosaic of stunted tree clumps, open woodlands, and herb- or dwarf-shrub-dominated openings, occurring above closed forest ecosystems and below alpine communities. It includes open areas with stands of whitebark pine (Pinus albicaulis) occurring most commonly on south-, east-, and west-facing aspects, or less commonly, alpine larch (Larix lyallii) on north-facing aspects and in basins with shallow rocky soils. Subalpine fir (Abies lasiocarpa) is the co-dominant in these systems and is often the most prevalent tree species. Engelmann spruce (Picea engelmannii) is usually associated with subalpine fir and occurs as either a climax co-dominant or as a persistent, long-lived seral species in most upper elevation subalpine fir habitat types. Whitebark pine may initiate tree islands at treeline sites, facilitating the establishment and growth of subalpine fir and Engelmann spruce which are less tolerant of harsh climatic conditions (Callaway, 1998; Tomback et al., 2014). Long-term absence of disturbance may enable these more shade tolerant species to succeed whitebark pine and alpine larch at these sites (Arno and Hoff, 1989). Elevations range from as low as 1,981 meters (6,500 feet) in northwestern Montana to 2,682 meters (8,800 feet) in southwestern Montana. At or above treeline, subalpine fir, spruce, and whitebark pine will often exhibit krummholz form and reproduce by layering as a result of the harsh climate and considerable snow accumulation typical of these sites.
The climate is typically very cold in winter and dry in summer. Landforms include ridgetops, mountain slopes, glacial trough walls and moraines, talus slopes, landslides and rockslides, and cirque headwalls and basins. Snow accumulation is high in basins, but ridgetops have little snow accumulation because of high winds and sublimation. In this harsh, often wind-swept environment, trees are usually stunted and flagged from damage associated with wind, blowing snow and ice crystals, especially at the upper elevations. Tree species that occur in the otherwise sparsely vegetated communities of this system are particularly important for wildlife and watershed hydrology as they provide important food sources and slow spring snowmelt, thereby increasing the duration of summer runoff and streamflow (Arno and Hoff, 1989). Fire suppression, disease, insects and climate change are changing the structure, distribution and composition of this system.
Subalpine or upper treeline; forest and woodland; oligotrophic soils.
Whitebark pine-subalpine fir forests and parklands occur throughout the Montana Rocky Mountains and east into the mountain island ranges. This is the most common forest alliance in the drier mountain ranges east of the Continental Divide. It is especially well represented in the Yellowstone Basin and surrounding mountain ranges. The distribution pattern of alpine larch (Larix lyalli) is patchy; the best stands occur near the treeline in the Anaconda-Pintlar, Bitterroot, Cabinet, Whitefish, Swan, southern Mission, Sapphire, and Flint Creek ranges, and in scattered locations in Glacier National Park and at the top of the headwaters of the Teton and Sun River drainages (Arno and Habeck, 1972). Mountain hemlock (Tsuga mertensiana)/subalpine fir is a minor subalpine forest type present in some high mountain cirques along the Montana-Idaho Divide from Lolo to the Cabinet Gorge. Mountain hemlock stands are much more prevalent immediately to the west in Idaho; however, they also occur in small isolated stands in the Whitefish, Mission, and Bitterroot ranges. They are absent from Glacier National Park.
Ecological System Distribution
Approximately 1,549 square kilometers are classified as Rocky Mountain Subalpine Woodland and Parkland in the 2017 Montana Land Cover layers.
Grid on map is based on USGS 7.5 minute quadrangle map boundaries.
Montana Counties of Occurrence
Beaverhead, Broadwater, Carbon, Cascade, Deer Lodge, Fergus, Flathead, Gallatin, Glacier, Golden Valley, Granite, Jefferson, Judith Basin, Lake, Lewis and Clark, Lincoln, Madison, Meagher, Mineral, Missoula, Park, Pondera, Powell, Ravalli, Sanders, Silver Bow, Stillwater, Sweet Grass, Teton, Wheatland
In Montana, these forests form a belt throughout the Montana Rocky Mountains and island ranges. Near the upper elevational limits, these forests and parklands are bordered by alpine meadows and tundra. On especially dry sites east of the Continental Divide, these forests are sometimes bordered by subalpine grasslands. Forests and parklands are diverse in composition and structure due to widely diverse high elevation terrain and extreme climatic conditions. At the upper limits of tree growth, stands and krummholz mats can persist for hundreds of years. This system occurs up to 1,981-2,195 meters (6,500-7,200 feet) in northwestern Montana, 2,225-2438 meters (7,300-8,000 feet) in west-central Montana and island ranges, and 2,469-2,682 meters (8,100-8,800 feet) in southwestern Montana. Soils and parent materials are variable. Alpine larch stands typically develop on granitic and quartzite substrates with little soil development or occasionally on sedimentary materials. Surface soils are usually gravelly loams with large amounts of rock present (Pfister et al., 1977). Whitebark pine-subalpine fir communities can occur on a wide range of parent materials, including calcareous bedrock substrates. Soils are typically gravelly silt loams and silts that range from slightly basic to slightly acidic. Duff layers in both forest types are typically less than 2.5 centimeters (1.0 inch) (Pfister et al., 1977). This forest and woodland system occurs on landforms such as ridgetops, mountain slopes, glacial trough walls and moraines, talus slopes, landslides and rockslides, and cirque headwalls and basins. Snow accumulation is high in basins, but ridgetops have little snow accumulation because of high winds and sublimation. In this harsh, often wind-swept environment, trees are stunted and flagged from damage associated with wind, blowing snow and ice crystals, especially at the upper elevational ecotone.
These forests or patches often originate when Engelmann spruce, alpine larch, or whitebark pine colonize a sheltered site. Alpine larch/subalpine fir communities are prevalent on cool, north- and east-facing exposures west of the Continental Divide. Whitebark pine/subalpine fir communities occur on adjacent, warmer exposures and aspects. Subalpine fir colonizes in the shelter of these speciesand may form a dense canopy by branch layering. This species is capable of remaining dominant within these subalpine and treeline forests due to its longevity and ability to regenerate vegetatively. In the absence of disturbance, it continues to regenerate under shaded conditions. Seed crops are erratic at the lower elevational limit of this system and are virtually absent at treeline. The most common subalpine forest association in Montana is whitebark pine-subalpine fir.
The understories of these forests are usually sparse, but moister sites support mats of ericaceous plants, such as tall huckleberry (Vaccinium membranaceum), dwarf bilberry (Vaccinium myrtillus), or most often, grouse whortleberry (Vaccinium scoparium). Mountain heath (Phyllodoce species) and white mountain heather (Cassiope mertensiana) are commonon sites with more organic matter accumulation. A few taller shrubs such as alpine currant (Ribes montigenum), short fruited willow (Salix brachycarpa), and planeleaf willow (Salix planifolia) may also be present.The herbaceous layer is sparse under dense shrub or tree canopies, but may be dense where the shrub canopy is open or absent. Purple mountain hairgrass (Vahlodea atropurpurea), Hitchcock’s woodrush (Luzula glabrata var. hitchcockii), alpine bluegrass (Poa alpina), Sandberg’s bluegrass (Poa secunda), alpine timothy (Phleum alpinum), pinegrass (Calamagrostis rubescens), Parry’s rush (Juncus parryi) and sedges (Carex species) are the most common graminoids. A wide diversity of forbs are present in open meadows among or adjacent to these forests, typically including species such as arnica (Arnica species), subalpine wandering daisy (Erigeron peregrinus), arrowleaf groundsel (Senecio triangularis), aster (Symphyotrichum species), sibbaldia (Sibbaldia procumbens), glacier lily (Erythronium grandiflorum), rhexi-leaf paintbrush (Castilleja rhexifolia), western windflower (Anemone occidentalis), alpine St. John’s wort (Hypericum formosum), diverse leaf cinquefoil (Potentilla diversifolia), and penstemon (Penstemon species).
Alpine larch stands generally occur at or near upper treeline in north-facing cirques or on slopes where snowfields persist until June or July (Arno and Habeck, 1972). Typical stands are often isolated pockets of open, parklike groves. Alpine larch is considered a pioneer species in these high, north-facing aspects on rocky sites with little soil development, and due to its longevity (up to 1,000 years), is persistent on these sites. Typically, undergrowth in alpine larch stands can be limited due to high rock cover and limited soil development, but will often includes pink mountain heath (Phyllodoce empetriformis), Hitchcock’s woodrush and subalpine fir.
National Vegetation Classification Switch to Full NVC View
Adapted from US National Vegetation Classification
A0631 Larix lyallii Woodland Alliance
CEGL000951 Larix lyallii - Vaccinium scoparium - Luzula glabrata var. hitchcockii Woodland
A3368 Pinus albicaulis Forest & Woodland Alliance
CEGL000127 Pinus albicaulis Woodland [Placeholder]
CEGL000128 Pinus albicaulis / Abies lasiocarpa Woodland
CEGL000129 Pinus albicaulis - Carex rossii Forest
CEGL000131 Pinus albicaulis - Vaccinium scoparium Forest
CEGL000752 Abies lasiocarpa / Pinus albicaulis - Vaccinium scoparium Woodland
CEGL000754 Pinus albicaulis / (Abies lasiocarpa) - Carex geyeri Woodland
CEGL000755 Pinus albicaulis - Festuca idahoensis Woodland
CEGL000756 Pinus albicaulis - Juniperus communis Woodland
CEGL005836 Pinus albicaulis / Abies lasiocarpa - Menziesia ferruginea - Xerophyllum tenax Woodland
CEGL005837 Pinus albicaulis / Abies lasiocarpa - Vaccinium membranaceum - Xerophyllum tenax Woodland
CEGL005838 Pinus albicaulis / Abies lasiocarpa - Vaccinium scoparium - Xerophyllum tenax Woodland
CEGL005839 Pinus albicaulis / Abies lasiocarpa - Vaccinium scoparium - Luzula glabrata var. hitchcockii Woodland
A3640 Abies lasiocarpa - Picea engelmannii - Pinus flexilis Dry-Mesic Rocky Mountain Krummholz Alliance
CEGL000985 Abies lasiocarpa / Picea engelmannii Krummholz
*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
Major disturbances in this system include fire, avalanches, and biotic vectors. Fires in this system have average return intervals of 170 years and are either mixed severity or stand replacing (U.S. Department of Agriculture, 2012). In general, stand-replacing fires occur less frequently, at least where open woodlands limit fire severity and spread (Arno, 1980). In stands where fire return intervals are longer or where fires have been suppressed, shade-tolerant subalpine fir becomes increasingly dominant. Tree species that occur in this system vary in their susceptibility to fire. Subalpine fir has thin bark and experiences high mortality from low-intensity burns (Uchytil, 1991), whereas whitebark pine has moderately thick bark, and mature trees can withstand low severity fires (Fryer, 2002). Lightning damage to individual trees is common, but sparse canopies and rocky terrain historically limited the spread of fire. More recently, stand-replacing fires caused by lightning strikes are becoming more common in part because woodlands have become increasingly dense due to fire suppression. Post-fire regeneration is dominated by shade-intolerant whitebark pine and alpine larch. Clark’s nutcrackers (Nucifraga Columbiana) are the primary disperser of whitebark pine seeds post-fire (Tomback, 2005). Near treeline, establishment of subalpine fir may take decades or longer to establish after fire in part due to the harsh climate characteristic of this system. Often, stand-initiating whitebark pine facilitate the establishment of later-successional species like subalpine fir and Engelmann spruce by ameliorating the harsh climatic conditions otherwise found at treeline sites (Callaway, 1998; Tomback et al., 2014).
Insects and disease are major forces of disturbance within this system. Whitebark pine is affected by white pine blister rust and mountain pine beetle (Dendroctonus ponderosae) and is experiencing marked decline. Infection rates of white pine blister rust, caused by the non-native pathogen Cronartium ribicola, have increased in recent decades. Blister rust infections are more likely to occur in microsites (Smith-McKenna et al., 2013) or years with relatively cool and humid conditions (Sturrock et al., 2011). Mortality due to blister rust is especially high in northwestern Montana, where the moister Pacific maritime climate at high elevations is more conducive to infection than the drier air in the southern mountain ranges (Smith et al., 2012). Blister rust has a tendency to kill cone producing branches in whitebark pine crowns. The resulting reduction in cone production strongly limits whitebark pine reproduction potential (McCaughey and Tomback, 2001). Mountain pine beetles, which historically occurred at endemic levels in lower subalpine forests, are causing an increased incidence of outbreak in treeline communities, causing mortality of mature whitebark pine. Additionally, beetles preferentially select trees with weakened defenses, such as those affected by blister rust or severe drought (Bockino and Tinker, 2012). Subalpine fir is becoming more prevalent in these forests due to high mortality caused by blister rust and mountain pine beetles.
Throughout Montana, both subalpine fir and spruce are affected by western spruce bud worm (Choristoneura occidentalis) attacks, although outbreaks are less common in high-elevation stands (Uchytil, 1991). Large stands of subalpine forests, however, can be killed following several years of drought or unusually mild winters. Subalpine fir in the northern Rocky Mountains is also susceptible to the fungus (Heterobasidion annosum) which causes root rot and may increase vulnerability to other biotic pathogens (Uchytil, 1991). Unlike other species in this system, alpine larch is relatively unaffected by insects or disease (Habeck, 1991).
Climate can also influence ecological processes in this system. Warming climate patterns may result in increased seedling recruitment and tree density at the upper elevation limit of this ecological system (Klasner and Fagre, 2002). Climate may have additional effects on biotic vectors. Mountain pine beetles, which were historically rare in this system due to cold temperatures, have become increasingly common as a result of changing temperature regimes (Bockino and Tinker, 2012). In addition, avalanches, which are common in precipitous mountain areas that receive heavy snowfall, cause stand-initiating disturbances that remove broad swaths of subalpine forest.
In the absence of natural fire, periodic low-severity prescribed burns can be implemented during late fall months to maintain, enhance, and restore this system. Fire facilitates nutrient cycling and encourages whitebark pine dominance in stands where succession by subalpine fir and Engelmann spruce is occurring (Arno and Hoff, 1989). Fire additionally creates open sites favorable to seed caching by Clark’s nutcrackers and exposes mineral soil seedbeds favored by whitebark pine and alpine larch. A long-term study in western Montana and eastern Idaho found that prescribed fire is likely most effective at restoring whitebark pine if burn sites are in close proximity to healthy whitebark stands, or if burning is followed by planting of rust-resistant nursery stock (Keane and Parsons, 2010). When selecting seed sources for supplemental planting, seed transfer guidelines should be followed to avoid maladaptation to site specific conditions (Bower and Aitken, 2008).
Restoration strategies will in part depend on degree of blister rust infection within a stand. Small-scale prescribed burning during late fall after several hard frosts is recommended to prevent succession by subalpine fir and facilitate whitebark pine regeneration by providing open sites on exposed mineral soils suitable for nutcracker seed caching and seedling establishment (Fryer, 2002). Blister rust damage reduces cone production and nutcracker seed caching (McKinney and Tomback, 2007). When blister rust infection within a region is severe, post-burn supplemental planting with genetically rust-resistant nursery stock may be necessary (Keane and Parsons, 2010). Similarly, large scale mountain pine beetle outbreaks may necessitate supplemental planting if regeneration is limited or blister-rust infection of surviving individuals is severe. When outplanting rust-resistant nursery stock is necessary, success can be improved by reducing seedling competition with overstory trees or understory grasses and sedges, and planting seedlings in microsites with favorable growth conditions, including on the leeward side of rocks and stumps (McCaughey et al., 2009).
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:
- 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);
- Evaluating structural characteristics and distribution of each ecological system 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 ecological system;
- 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: mtnhp.org/requests
) 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.
- 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.
- Native Species Commonly Associated with this Ecological System
- Native Species Occasionally Associated with this Ecological System
Original Concept Authors
Montana Version Authors
- Classification and Map Identifiers
Cowardin Wetland Classification:
National Land Cover Dataset:
|Element Global ID
||CES306.807, Northern Rocky Mountain Subalpine Woodland and Parkland
42: Evergreen Forest
4233: Northern Rocky Mountain Subalpine Woodland and Parkland
- Literature Cited AboveLegend: View Online Publication
- Arno, S.F. and R.J. Hoff. Silvics of whitebark pine (Pinus albicaulis). 1989. General Technical Report INT-253. Ogden, UT. USDA, Forest Service, Intermountain Research Station. 11pp.
- Bockino, N.K.and D.B. Tinker. 2012. Interactions of white pine blister rust and mountain pine beetle in whitebark pine ecosystems in the southern Greater Yellowstone Area. Natural Areas Journal 32(1):31-40.
- Bower, A.D. and S.N. Aitken. 2008. Ecological genetics and seed transfer guidelines for Pinus albicaulis (Pinaceae). American Journal of Botany 95(1):66-76.
- Callaway, R.M. 1998. Competition and facilitation on elevation gradients in subalpine forests of the northern Rocky Mountains, USA. Oikos 561-573.
- Fryer, J.L. 2002. Pinus albicaulis. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
- Habeck, R. J. 1991. Larix lyallii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
- Keane, R.E. and R.A. Parsons. 2010. Restoring whitebark pine forests of the northern Rocky Mountains, USA. Ecological Restoration 28(1):56-70.
- McCaughey, W., G.L. Scott,and K.L. Izlar. 2009. Technical note: whitebark pine planting guidelines. Western Journal of Applied Forestry 24(3):163-166.
- McCaughey, W.W. and D.F. Tomback. 2001. The natural regeneration process. pp105-120. In: Whitebark pine communities: ecology and restoration. Washington D.C.: Island Press.
- McKinney, S.T. and D.F. Tomback. 2007. The influence of white pine blister rust on seed dispersal in whitebark pine. Canadian Journal of Forest Research 37(6);1044-1057.
- Smith, C.M., B. Shepherd, C. Gillies,and J. Stuart-Smith. 2012. Changes in blister rust infection and mortality in whitebark pine over time. Canadian journal of forest research 43(1):90-96.
- Smith-Mckenna, E.K., L.M. Resler, D.F. Tomback, H. Zhang, and G.P. Malanson. 2013. Topographic influences on the distribution of white pine blister rust in Pinus albicaulis treeline communities. Ecoscience. 20:(3): 215-229.
- Sturrock, R.N., S.J. Frankel, A.V. Brown, P.E. Hennon, J.T. Kliejunas, K.J. Lewis, and A.J. Woods. 2011. Climate change and forest diseases. Plant Pathology 60(1):133-149.
- Tomback, D.F. 2005. The impact of seed dispersal by Clark’s nutcracker on whitebark pine: multi-scale perspective on a high mountain mutualism. pp. 181-201. In: Mountain Ecosystems. Springer Berlin Heidelberg.
- Tomback, D.F., K.G. Chipman, L.M. Resler, E.K. Smith-McKenna, and C.M. Smith. 2014. Relative abundance and functional role of whitebark pine at treeline in the Northern Rocky Mountains. Arctic, Antarctic, and Alpine Research 46(2):407-418.
- U.S. Department of Agriculture, Forest Service, Missoula Fire Sciences Laboratory. 2012. Information from LANDFIRE on Fire Regimes of Whitebark Pine Communities. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service
- Uchytil, R.J. 1991. Abies lasiocarpa. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
- Additional ReferencesLegend: View Online Publication
Do you know of a citation we're missing?
- Arno, S. F. 1980. Forest fire history in the northern Rockies. Journal of Forestry 78(8):460-465.
- Arno, S.F., and J.R. Habeck. 1972. Ecology of alpine larch (Larix lyallii Parlatore) in the Pacific Northwest. Ecological Monographs 42(4):417-450.
- Klasner, Frederick L., and Daniel B. Fagre. 2002. "A Half Century of Change in Alpine Treeline Patterns at Glacier National Park, Montana, U.S.A.". Arctic, Antarctic, and Alpine Research. 34 (1): 49-56.
- McCaughey, W. 1990. Biotic and microsite factors affecting Pinus albicaulis establishment and survival. M.S. thesis, Montana State University, Bozeman. 78 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.