Alpine Bedrock and Scree
Provisional State Rank
This ecological system is restricted to the highest elevations of the Rocky Mountains, from Alberta and British Columbia south into New Mexico, and west into the highest mountain ranges of the Great Basin. It is composed of barren and sparsely vegetated alpine substrates, typically including both bedrock outcrop and scree slopes, with lichen- dominated communities. In Montana, alpine bedrock and scree are well represented throughout the northern Rocky Mountains and island mountain ranges. Elevations range from as low as 2,285 meters (7,500 feet) in northwestern Montana to 3,500 meters (11,500 feet) in southern Montana. Exposure to desiccating winds, rocky and sometimes unstable substrates, and a short growing season limit plant growth. Typically, there is sparse (less than 10%) cover of forbs, grasses, and low shrubs, with exposed, unstable scree, talus and bedrock constituting the remainder of cover. Diverse crustose and foliose lichen cover is high (often greater than 50%) on exposed talus and bedrock Soils on these windy, unproductive sites are very poorly developed, often only occurring in fractures of bedrock. This system is characterized by a very cold climate during winter, high winds, high UV radiation and high surface daytime temperatures during summer months on south and west facing aspects, and a very short growing season. Most scree- and bedrock-inhabiting plants are highly adapted to this xeric environment and occur as singular plants among the exposed rocks or in bedrock fractures. These species are typically cushioned, matted or succulent, or grow as flat rosettes, often with thick leaf cuticles or a dense cover of hairs. This system often occurs adjacent to or immediately below North American Alpine Ice Fields and intermingles with Rocky Mountain Alpine Fell Fields.
Alpine; talus and scree; rock outcrops; alpine slopes; shallow soils; less than 10% vascular cover.
This system occurs on mountain summits and the steep slopes immediately below summits throughout the Rocky Mountains and island mountain ranges of central and southern Montana. Elevation ranges from as low as 2285 meters (7,500 feet) in northwestern Montana to 3,505 meters (10,500 feet) in southern Montana.
Ecological System Distribution
Approximately 1,440 square kilometers are classified as Alpine Bedrock and Scree 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, Flathead, Gallatin, Glacier, 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
These steep, wind-scoured, loose talus and scree fields and exposed bedrock are often blown free of snow during winter, exposing plants to severe environmental stress. Soil development is very limited, and soils are usually gravelly and rocky. Soils are derived from a variety of parent materials, and can be acidic or calcareous. Organic matter is typically only found in very limited quantities in pockets among boulders, or in fractures or the leeside of the bedrock slabs. This system is characterized by a very cold climate and high winds during winter, and by high winds, high UV radiation and high surface daytime temperatures during summer months, especially on south and west facing aspects. Unstable scree and talus, isolated boulder pockets and exposed bedrock constitute at least half of the cover.
Plant cover is usually less than 10% with exposed, unstable scree, talus and bedrock constituting the remainder of cover. Most scree and bedrock inhabiting plants are highly adapted to this xeric environment and occur as singular plants among the exposed rocks or in bedrock fractures. These species are typically cushioned, matted or succulent, or grow as flat rosettes, often with thick leaf cuticles or a dense cover of hairs. Diverse crustose and foliose lichen cover is high (often greater than 50%) on exposed talus and bedrock. Common lichen genera include Rhizocarpon, Xanthoria, Lecidea, and Umbilicaria species. Mosses are typically found in bedrock fractures and the leeside of bedrock slabs and chutes below the summits, especially on the north and east facing aspects.
Forbs occur singly or in small patches among the exposed talus and scree and in fractures of the bedrock or the leeside of bedrock where organic matter has accumulated. In northwestern Montana, common forbs include yarrow (Achillea millefolium), elliptic leaf penstemon (Penstemon ellipticus), phacelia (Phacelia species), alpine sky pilot (Polemonium viscosum), alpine spring beauty (Claytonia megarhiza), alpine sandwort (Minuartia species), cut-leaf daisy (Erigeron compositus), draba (Draba spp.), boreal crazyweed (Oxtropis borealis), silky crazyweed (Oxytropis sericea), wooly groundsel (Senecio canus), alpine arnica (Arnica alpina), moss campion (Silene acaulis), spotted saxifrage (Saxifraga bronchialis), alpine buckwheat (Eriogonum ovalifolium), alpine forget-me-not (Myosotis alpestris) and Siberian aster (Symphyotrichum sibiricus). Woody species such as arctic dryad (Dryas octopetala), shrubby cinquefoil (Dasiphora fruticosa) and rock willow (Salix vestita) occur in bedrock fractures or the lee side of bedrock and boulders. Saxifrages and ferns also occur in these protected microsites.
Several northern Rocky Mountain endemic species, Montana species of concern, and potential species of concern inhabit this system. In Montana, some arctic species reach their southernmost range limit within this system, while some middle and southern Rocky Mountain species reach their northernmost range limit, particularly in southwestern ranges of the state.
Graminoid cover is usually very low and often occurs within patches and mats of forbs or woody species. In northwest Montana, common species include Dunhead sedge (Carex phaeocephala), spike sedge (Carex nardina), curly sedge (Carex ruprestris), single spike sedge (Carex scirpoidea), black and white sedge (Carex albonigra), spiked woodrush (Luzula spicata), Drummond’s rush (Juncus drummondii), alpine blue grass (Poa alpina), spike trisetum (Trisetum spicatum) and slender wheatgrass (Elymus trachycaulus). In southwestern Montana, other species are common, such as blackroot sedge (Carex elynoides), Parry’s rush (Juncus parryi), Idaho fescue (Festuca idahoenisis), spike fescue (Festuca kingii), and sheep fescue (Festuca ovina) (Cooper et al. 1999).
National Vegetation Classification Switch to Full NVC View
Adapted from US National Vegetation Classification
A3155 Carex elynoides - Carex rupestris - Kobresia myosuroides Rocky Mountain Alpine Turf Alliance
A3741 Aquilegia flavescens - Phacelia hastata Cliff, Scree & Rock Alliance
CEGL005899 Aquilegia flavescens / Senecio megacephalus Sparse Vegetation
CEGL005901 Phacelia hastata / (Penstemon ellipticus) Sparse Vegetation
A4021 Rocky Mountain Alpine Sparse Herb Bedrock & Scree Alliance
CEGL005900 Athyrium americanum / Cryptogramma acrostichoides Alpine Sparse Vegetation
CEGL005902 Saxifraga bronchialis Scree Slope Alpine Sparse Vegetation
CEGL005903 Saxifraga mertensiana Alpine Cliff Crevice
A4022 Rocky Mountain Alpine Nonvascular Bedrock & Scree 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
Historically, stand-replacing fires occurred infrequently in adjacent associated upper elevation subalpine woodlands (Arno, 1980). Lightning strikes can cause fire within these systems, although severity and spread is usually very limited. Changing climatic patterns will impact this system and the range of the peripheral species, northern Rocky Mountain endemics and rare species occurring within it.
This system is fragile due to extreme limited growing season and soil development, but occurs on sites accessable only by off-trail travel and climbing.
Generally, human disturbances are very limited in this system due to inaccessibility.
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