Montana Field Guide

This alpine community consists of exposed rock and rubble with very little vascular plant cover, occurring at or above the upper treeline in the mountains of western and central Montana. It is dominated by barren and sparsely vegetated alpine substrates, including bedrock outcrops, and talus and scree slopes occurring on upper mountain slopes, ridges and summits. Sparse cover of forbs, grasses, low shrubs and krummholz may be present with total vascular plant cover generally less than 10%, occasionally up to 25%. The high coverage of exposed rock limits the potential for additional vascular plant growth. Lichen-dominated communities covering the rock substrate are common and may greatly exceed 25% cover in some areas. The lower elevational limit for the alpine zone varies with latitude and aspect, ranging from about 8,000-9,500 feet in the southern part of the state to 6,000-7,000 feet in northwest Montana. Exposure to desiccating winds, rocky and sometimes unstable substrates, and a short growing season limit vascular plant growth. Unstable scree and talus, isolated boulder pockets and exposed bedrock constitute the majority of the surface cover. This group may occur as small patches intermingled with other alpine vegetation or as large discreet patches. In some areas it may transition seamlessly into G565 Rocky Mountain Cliff, Scree & Rock Outcrops Group below the upper treeline.

This Group is equivalent to the Alpine Bedrock and Scree Ecological System.

Alpine; Treeline; Talus and Scree; Rock Outcrops; Alpine Slopes; Shallow, Patchy Soils; Less than 25% Vascular Plant Cover.

This type occurs in all the higher elevation mountain ranges in Montana that have some area above treeline.

In Montana, G571 is confined to areas within or immediately adjacent to Level IV Ecoregions 15h (High Northern Rockies), 16h (High Idaho Batholith), 17h (Middle Rockies Alpine Zone) and 41b Canadian Rockies Crestal Alpine-Subalpine Zone.

In Montana, G571 occurs within these Major Land Resource Areas: 43A-Northern Rocky Mountains and 43B-Central Rocky Mountains.

Large Patch

This community occurs above treeline in the alpine zone which starts at about 9,000 feet in the southern part of the state to as low as 6,000 feet in northwest Montana. It is composed of barren and sparsely vegetated alpine substrates, including bedrock outcrops, and talus and scree slopes, occurring on upper mountain slopes, ridges and summits. Igneous, metamorphic and/or sedimentary rocks alone or in combination may form the substrate of this type. It may occur on all aspects and slopes though is more common on moderate to steep slopes. Exposure to desiccating winds, rocky and sometimes unstable substrates, heavy snow loads, and a short growing season limit vascular plant growth. Steep, wind-scoured, talus and scree fields and exposed bedrock are often blown free of snow during winter, exposing plants to severe environmental conditions.

Soil development is very limited, and soils are usually very shallow, patchy, and gravelly or rocky. The limited soils can be either acidic or calcareous depending upon the local parent material. Organic matter is typically only found in very limited quantities in pockets among boulders, or in fractures or crevices. This system is characterized by a very cold climate and high winds during winter, and by high winds, and high UV radiation during the summer months. South and west-facing slopes may experience relatively high, daytime, surface temperatures during the summer. Annual precipitation in these alpine environments typically ranges from 30-70 inches with significant amounts of that falling as snow for more than half the year.

Plant cover in this alpine community is often less than 10% with exposed, unstable scree, talus and bedrock constituting the remainder of cover. Sparse cover of forbs, grasses, low shrubs and krummholz may be present with total vascular plant cover less than 25% due to the high cover of exposed rock. Most scree and bedrock inhabiting plants are highly adapted to this harsh 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 rosettes, often with thick leaf cuticles or a dense cover of hairs. Vascular plants growing on loose substrates typically have either an extensive, shallow root and rhizome system or a large taproot that anchors the plant.

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. Forb species occurring in these habitats are many and vary across the state. In northwestern Montana, common forbs include, Common Yarrow (Achillea millefolium), Penstemon ellipticus, Phacelia species, Polemonium viscosum, Alpine Springbeauty (Claytonia megarhiza), Sandworts (Minuartia species), Cut-leaf Daisy (Erigeron compositus), Draba species, Oxytropis borealis, Oxytropis sericea, Senecio canus, Arnica alpina, Moss Campion (Silene acaulis), Spotted Saxifrage (Saxifraga bronchialis), Buckwheat (Eriogonum ovalifolium), Alpine Forget-me-not (Myosotis alpestris) and Eurybia sibirica. Shrubs and subshrubs such as Mountain-avens (Dryas hookeriana), Shrubby Cinquefoil (Dasiphora fruticosa) and Rock Willow (Salix vestita) may be present. In southwestern Montana, common forbs include Common Yarrow (Achillea millefolium), Lanceleaf Stonecrop (Sedum lanceolatum), Draba species, Fleabanes (Erigeron species), Potentilla species, and Alpine Smelowskia (Smelowskia calycina). Several species of ferns may also occur in protected microsites within this habitat across the state.

Graminoid cover is usually very low and often occurs within small patches and mats of forbs or woody species. Common species vary somewhat by geography but include Carex albonigra, Carex elynoides, Carex phaeocephala, Carex nardina, Carex ruprestris, Carex scirpoidea, Luzula spicata, Juncus drummondii, Parry’s rush (Juncus parryi), Idaho Fescue (Festuca idahoenisis), Poa alpina, and Trisetum spicatum. (Cooper et al. 1999; Lesica etal 1997).

Crustose and foliose lichen cover may be high (sometimes greater than 50%) on certain types of 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. Several northern Rocky Mountain endemic species and Montana Species of Concern inhabit these alpine communities.

Currently only two Alliances and four Associations within the National Vegetation Classification are described and attributed with occurring in MT. Additional plant communities probably occur within this Group in MT, either undocumented or undescribed, or not currently attributed to MT.

High winds and desiccation, heavy snow loads, short growing seasons, and unstable slopes and surfaces are the dominant processes in this alpine environment.

Extremely limited growing seasons, limited soil development and often poor access into these habitats limit potential uses and impacts.

K.A. Schulz 2015

S. Mincemoyer, L. Vance, T. Luna

11/25/2024