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Community Field Guide

Scientific Name:
Dryas octopetala - Polygonum viviparum Dwarf Shrub Herbaceous Vegetation

Common Name:
White dryas - serpent-grass Dwarf-shrub Herbaceous Vegetation

Community Description

Summary:
This association is a minor type that has been substantiated from throughout the alpine of southwestern and central Montana, and is likely to occur as far north as Canada's Jasper National Park and south to Colorado's Front Range. Mean elevation is 2915 m. The three described stands occur on gentle to steep slopes with northern aspects. Soils are typically sandy clay derived from limestone (or other calcareous substrate) and quartzite. Gravel content of soil ranges from 5-30%. Soil moisture content during the growing season is high. Disturbance from solifluction, slumps, and earthflows is common. A dwarf-shrub layer dominates the vegetation cover of this community. Dryas octopetala forms mats that range 30-80% in cover. Salix reticulata (5-20% cover) is common and may codominate. The herbaceous layer is sparse (<20% cover) and is dominated by the forbs Polygonum viviparum, Polygonum bistortoides, Zigadenus elegans, and Oxytropis borealis var. viscida (= Oxytropis viscida). Graminoid cover is low (<5%) and mostly composed of Carex elynoides, Carex rupestris, and Festuca brachyphylla. Moss and lichen cover are high on some plots (>50%). Diagnostic of this alpine association is a dwarf-shrub layer dominated by Dryas octopetala with Polygonum viviparum dominant in the herbaceous layer. This description is based on data from three plots in southwestern Montana.

Environment:
This minor type was found in both the wettest, (Anaconda and Madison) and driest (Tendoy) ranges. Small occurrences of this type were noted but not sampled in other mountain ranges. This vegetation was generally found on northerly facing gentle- to steep-slopes. Evidence of disturbance, including solifluction, slumps and earthflows, were also common. Only trace amounts of rock were exposed but gravel ranged from 5%-30%.

Vegetation:
Mats of Dryas octopetala, ranging in cover from 30% to 80% and Salix reticulata (5%-20% canopy cover) provided the dominant aspect of this community type. Graminoid canopy cover was low, not exceeding 5%, and composed of the common turf species Carex elynoides, Carex rupestris, and Festuca ovina, as well as Poa alpina. Average forb cover was also relatively low, 14%, with dominance shared among the diagnostic species for the type, Polygonum viviparum, Polygonum bistortoides, Zigadenus elegans and Oxytropis viscida. Other forbs with high constancy, low coverage and some degree of fidelity to this type were Lloydia serotina, Senecio crassulus, Smelowskia calycina, Oxytropis campestris and Pedicularis cystopteridifolia. Two plots had moss and lichen coverages in excess of 50% adding to the impression of a smooth blanket of vegetation.

Range:
This association has been substantiated from throughout the alpine of southwestern Montana (Beaverhead Mountains Section) with occurrences in Glacier NP and the Big Snowy Mountains of central Montana. The association is likely to occur as far north as Canada's Jasper NP and south to Colorado's Front Range. Additional inventory will probably find additional occurrences Rocky Mountain Front Range of Montana.

Global Rank: G3? State Rank: S2

Global Rank Comments:
This association has been formally named based on only three sample plots from southwestern Montana ranges (Tendoy, Anaconda-Pintlar, Madison) which lie wholly within the Beaverhead Mountains Section. However, it appears this, or a compositionally quite similar association, occurs in Glacier National Park, Big Snowy Mountains (central Montana) and the Flint Creek Range (immediately north of Anaconda-Pintlar Range) of Montana. The habitats of these sites, notably moist sites on calcareous substrates, match closely those described for southwestern Montana. The Canadian literature also describes similar vegetation types occurring in similar environments. In Colorado, moist Dryas octopetala-dominated fell-fields with Polygonum viviparum have been described, but dwarf Salix spp. were not a component. A formal crosswalking has not been conducted amongst these various representations of what could be one association, but citations are sufficient to reduce its suspected rarity to a G3 rank. An additional factor is that potential threats to this association, grazing by sheep and roading, are minor. Concern could stem from off-road vehicle use (ATVs for example) as these sites are generally fragile, especially when their moisture status is high.

Community References

Identifier:
CEGL001894

Author:
97/10 / S. V. Cooper et al.

Citations:
Bamberg and Major 1968, Bourgeron and Engelking 1994, Cooper and Lesica 1992, Cooper et al. 1997, Cooper et al. 1999, Driscoll et al. 1984, Nesser et al. 1997

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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