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Community Field Guide

Scientific Name:
Pseudoroegneria spicata - Bouteloua curtipendula Herbaceous Vegetation

Common Name:
Bluebunch wheatgrass - sideoats grama Mixedgrass

Community Description

Summary:
This mixedgrass association ranges in size from small to large patches which are located on foothills and sideslopes along major drainages between the Tongue and Powder rivers of southeastern Montana. This type is considered a topo-edaphic climax by Hansen and Hoffman (1988) because it occurs on moderate to steep (>45%) slopes the surfaces of which are strewn with large amounts of irregularly shaped, iron oxide porcelainite shale (scoria). The surface resulted from fires in contiguous coal beds (but the soils are conventional loams). The harsh sites of this type result in a unique depauperate community with the lowest total cover and graminoid cover of any southeastern Montana type inventoried by Hansen and Hoffman (1988). However, it still has greater cover and is more productive than those communities associated with bentonite deposits and acid shales. Pseudoroegneria spicata is strongly dominant (canopy cover ranging from 40-60%) with Bouteloua curtipendula exhibiting less than one-fourth this value. Pascopyrum smithii (= Agropyron smithii) and Schizachyrium scoparium are consistently present with cover less than 10%. Forbs are a minor component with Lygodesmia juncea, Echinacea angustifolia and Pediomelum argophyllum (= Psoralea argophylla) having the highest fidelity to the type.

Environment:
This type occurs as small to large patches located on foothills and sideslopes along major drainages between the Tongue and Powder rivers of southeastern Montana; known elevations range between 3100 and 3800 feet. This type is considered a topoedaphic climax by Hansen and Hoffman (1988) because it occurs on moderate to steep (>45%) slopes, the surfaces of which are strewn with large amounts of irregularly shaped, iron oxide porcelainite shale (scoria) that has resulted from ancient fires in contiguous coal beds. The soils are conventional loams but shallow and excessively drained.

Vegetation:
Pseudoroegneria spicata is strongly dominant (canopy cover ranging from 40-60%) with Bouteloua curtipendula exhibiting less than one-fourth this cover value. Pascopyrum smithii (= Agropyron smithii) and Schizachyrium scoparium are consistently present with cover less than 10%. Forbs are a minor component with Lygodesmia juncea, Echinacea angustifolia and Pediomelum argophyllum (= Psoralea argophylla) having the highest fidelity to the type. The shrubs (subshrubs) Rhus trilobata, Gutierrezia sarothrae and Artemisia frigida are consistently present with low coverage values (less than 5%).

Range:
This association has been recorded for only southeastern Montana, though appropriate habitat ostensibly occurs in northeastern Wyoming and westernmost North Dakota.

Dynamics:
Given the low cover and patchiness of this type, fires probably burned in a mosaic fashion with reduced intensity. Pronghorn antelope use these sites for grazing and predator detection.

Global Rank: G3 State Rank: S3

Global Rank Comments:
As currently understood, this type is restricted both geographically and with regard to site parameters. However, appropriate habitat in Wyoming overlaps the distribution of the characteristic species, so inventory may yield more occurrences. Threats to this type could potentially come from domestic stock, but sites are generally somewhat removed from water. These sites are generally not conducive to alien Bromus species, but their potential to support other weeds is unknown.

Community References

Identifier:
CEGL001663

Author:
S.V. Cooper

Citations:
Bourgeron and Engelking 1994, Driscoll et al. 1984, Hansen 1985, Hansen and Hoffman 1988

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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