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Community Field Guide

Scientific Name:
Dryas integrifolia - Carex spp. Dwarf Shrub Herbaceous Vegetation

Common Name:
Entire-leaved avens - sedge spp. Dwarf-shrub Herbaceous Vegetation

Community Description

Summary:
This association is documented only from the alpine zone of the Big Snowy Mountains of north-central Montana, though reconnaissance information places it as well in the Tobacco Root Range of southwestern Montana. Stands occur from 2360-2700 m (7750-8850 feet) elevation on gently sloping topography developed on Madison Limestone. This substrate is resistant to chemical weathering, but has been acted upon by frost to produce stepped terraces, rock polygons, sorted/non-sorted frost boils, and 'spotted tundra' (oval, spaced mats of Dryas integrifolia surrounded by rock rubble) and solifluction lobes on lee slopes. Soils are shallow, alkaline, cobbly and covered by a layer of gravels and rock fragments. The mat-forming dwarf-shrub Dryas integrifolia and turf-forming and perennial sedge Carex rupestris are diagnostic for the type and dominate small vegetated patches that are regularly interspersed in a matrix of unvegetated to sparsely vegetated rocky ground. Carex scirpoidea ssp. pseudoscirpoidea (= Carex pseudoscirpoidea), Saxifraga oppositifolia, Polygonum viviparum, Oxytropis sericea, Androsace chamaejasme and Lloydia serotina have high constancy but their individual cover seldom exceeds 5%. This association, in both floristic and environmental param (with some local variation in the forb component), is highly similar to Dryas octopetala - Carex rupestris Dwarf-shrub Herbaceous Vegetation (CEGL001892) which is found from the Canadian Rockies south to Colorado.

Environment:
This association occurs from 7550 to 8850 feet elevation in the alpine of an isolated mountain range (separated from the main crest of the Rockies by 240 km). The climate is unusual, in that there is a distinct summer peak of precipitation and a winter minimum. Summers are cool and winters cold. The geologic substrate is Madison limestone, and has formed a gentle topography of low relief. The limestone is very resistant to chemical erosion, but is mechanically fractured and has been shaped into numerous frost-patterning phenomena. Soils are very shallow, alkaline and cobbly, with carbonate accumulations in the lower horizons and high clay content. The surface is covered with a layer of small gravel and rock fragments 5-18 cm deep, overlying small ridges of soil. The top soil horizon is characterized by organic enrichment (26% organic matter). The soils are unstable and in a constant state of change due to the action of frost.

Vegetation:
This is an alpine tundra association dominated by the low, mat-forming evergreen shrub Dryas integrifolia and the perennial sedge Carex rupestris. The mats of Dryas and Carex occur within a matrix of active frost-patterned bare soil, cobbles and rocks. Most other species occurring in this association are found within these Dryas mats. In addition to the abundant or constant species, the perennials Aquilegia jonesii, Physaria didymocarpa, Rhodiola rosea (= Sedum rosea), and Saxifraga oppositifolia grow scattered in the rock rubble covering the soil. Richness is relatively low compared to other Rocky Mountain alpine tundras.

Range:
This association is documented only from the alpine zone of the Big Snowy Mountains of north-central Montana, though reconnaissance information places it as well in the Tobacco Root Range of southwestern Montana.

Global Rank: G3Q State Rank: S3

Global Rank Comments:
This type's rank has been lowered from G2? to G3Q. Although this association is apparently restricted to the Big Snowy Mountains of north-central Montana, it is quite abundant and secure within that landscape. There are no existing threats from mining, domestic stock grazing or recreation, the only possible threats to its security. The Q has been added due to the questioned taxonomy of the Dryas sp. If in fact, the Dryas sp. is the more common Dryas octopetala, then the Montana examples (plots) are quite congruent with the description offered for Dryas octopetala - Carex rupestris Dwarf-shrub Herbaceous Vegetation (CEGL001892).

Community References

Identifier:
CEGL001890

Author:
M.S. Reid, mod. S.V. Cooper

Citations:
Bamberg 1961, Bamberg and Major 1968, Bourgeron and Engelking 1994, Driscoll et al. 1984, Tuhy and Jensen 1982, UNESCO 1973

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This information is from the:
Montana Natural Heritage Program
Montana State Library--Natural Resource Information System
1515 East Sixth Ave., Helena, MT 59620-1800
406 444-5354
http://mtnhp.org
mtnhp@mt.gov