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Community Field Guide

Scientific Name:
Geum rossii - Minuartia obtusiloba Herbaceous Vegetation

Common Name:
Ross' avens - alpine stitchwort Herbaceous Vegetation

Community Description

Summary:
This plant association has been documented from southwestern Montana in the East Pioneer and Tobacco Root ranges. Stands are found on thin soils weathered from crystalline parent materials. This type is common on exposed, wind-swept, upper slopes, slope shoulders, saddles and ridgetops at elevations of 2990-3230 m (9800-10,600 feet). Extreme winds create a deflation surface with bare ground and gravel comprising nearly 50%, with much of the remainder cloaked by cushion plants. Soils are slightly acidic, have 35-70% coarse fragments and are predominantly well-drained sandy loams. Structurally this is a cushion plant community with virtually no dwarf-shrub component and a graminoid component reduced to an average of only 4% cover. Only Festuca brachyphylla (= Festuca ovina) exhibits greater than 5% cover and high constancy; Luzula spicata, Carex elynoides and Poa glauca are at least 50% constant, with low coverage. Mean forb cover is 30% with Geum rossii and Minuartia obtusiloba being 100% constant and together constituting about one-quarter to one-half of the total forb cover. Other important cushion plants are Eritrichium nanum, Phlox pulvinata, Douglasia montana, and Silene acaulis. Selaginella densa and Selaginella watsonii are locally abundant. This is the most characteristic cushion plant/fell-field community of southwestern Montana and is identified by the dominance of the diagnostic species Geum rossii and Minuartia obtusiloba, which sets it apart from other cushion plant communities, such as Phlox pulvinata - Trifolium dasyphyllum Herbaceous Vegetation (CEGL001980) and Antennaria microphylla - Artemisia scopulorum Herbaceous Vegetation (CEGL001847). However, there are other Rocky Mountain cushion plant communities, for instance those of the White Cloud Peaks, Idaho, and Beartooth Mountains, Montana, dominated by and named for Geum rossii, which may be similar, if not synonymous, with the community described here.

Environment:
Geum rossii / Minuartia obtusiloba is common on exposed, windswept upper slopes, saddles and ridgetops between 9,800 and 10,400 feet in the Pioneer and Tobacco Root ranges. This type occurred only on soils developed from crystalline parent material. This sparsely vegetated association usually graded into the Carex scirpoidea / Geum rossii turf community having deeper soils and protected exposures.

Vegetation:
Mean graminoid cover was only 4%. Festuca ovina was the only graminoid commonly present in appreciable amounts (canopy cover not exceeding 10%). Luzula spicata and Carex elynoides had low coverage but were frequent, and Carex rupestris and Trisetum spicatum were locally common. Mean cover of forbs was 30%. Geum rossii had the greatest constancy and cover of any forb; Minuartia obtusiloba (formerly Arenaria obtusiloba), Eritrichium nanum, Phlox pulvinata and Silene acaulis were common cushion plants. Selaginella densa and Selaginella watsonii were locally abundant. Trace amounts of the shrubs, Ribes hendersonii and Dryas octopetala, occurred in one stand. Cover of mosses and lichens was less than 1%.

Global Rank: G3? State Rank: S3

Global Rank Comments:
The rank change, from G3 to G3?, reflects the lack of knowledge concerning the association and that it has not been adequately inventoried, even from the region from which it was first described (southwestern Montana). Given that habitat for this type is potentially extensive, that the diagnostic and constituent species exhibit considerable range and that there are virtually no threats to the type, then its rank should probably be lowered to G4 or G5 pending future inventory.

Community References

Identifier:
CEGL001965

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

Citations:
Bourgeron and Engelking 1994, Cooper and Lesica 1992, Cooper et al. 1997, Driscoll et al. 1984, Johnson and Billings 1962, Potkin and Munn 1989, Richardson and Henderson 1999

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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