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Community Field Guide

Scientific Name:
Pseudoroegneria spicata - Eriogonum brevicaule Sparse Vegetation

Common Name:
Bluebunch wheatgrass - short-stem wild buckwheat Sparse Vegetation

Community Description

This sparse vegetation association occurs within the Bighorn Basin of south-central Montana. The habitat consists of very arid, steep, highly eroded and eroding slopes with southern or western aspects. These 'badland' environments form a band on the slopes of the Pryor Mountains from 1280-1525 m elevation. This community likely occurs in similar 'badlands' habitats in adjacent areas in Wyoming. Soils are deep, alkaline sandy clay or clay derived from shale, bentonite, claystone or sandstone interbedded with clay. The soil surface has high cover of gravel and cobbles. Cryptogamic soil crusts may form on gentler, less disturbed slopes. The total vegetation cover is typically less that 25% and is typically codominated by the cool-season, medium-tall bunchgrass Pseudoroegneria spicata (7% mean cover) and the warm-season, perennial forb Eriogonum brevicaule (8% mean cover). Other species may include scattered shrubs, such as Ericameria nauseosa (= Chrysothamnus nauseosus), Gutierrezia sarothrae, Atriplex confertifolia, the grasses Achnatherum hymenoides (= Oryzopsis hymenoides) and Poa secunda, and the forbs Arenaria hookeri, Cryptantha spp. and Machaeranthera grindelioides. Stands are characterized by a sparse herbaceous layer that is codominated by Pseudoroegneria spicata and Eriogonum brevicaule.

This association is apparently restricted to conditions obtaining within the Bighorn Basin Section of Montana. The combination of very arid climate and steep, highly eroded and eroding slopes provides appropriate habitat, therefore this association can be speculated to occur in Wyoming as well. Some very similar conditions obtain in southeastern Montana, but within Montana Eriogonum brevicaule occurs in only Carbon and Big Horn counties.

Global Rank: G3? State Rank: S2

Global Rank Comments:
Characterized in part by its sparse vegetation, this plant association has been described only from the northernmost portion of the Bighorn Basin Section, on the southern and western slopes of the Pryor Mountains. The eight sampled stands occurred predominantly on steep and highly eroded slopes (badlands terrain) of shale, bentonite, claystone or sandstone (interbedded with clay); these substrates weather to deep "soils" of clay to sandy clay texture with high cover of surface gravel and cobbles. The conjunction of badlands substrates of limited exposure with a highly arid mesoclimate produces a unique environment within Montana, though similar environments may exist within Wyoming's portion of the Bighorn Basin Section. Similar associations on comparable substrates occur in southeastern Montana, but Eriogonum pauciflorum replaces Eriogonum brevicaule as the most common forb and the climatic regime is less arid. Threats to this type are virtually non-existent and therefore it cannot be said to be imperiled and deserves a G3 with ? added pending inventory of Wyoming's portion of Bighorn Basin Section.

Community References


S.V. Cooper

Bourgeron and Engelking 1994, DeVelice and Lesica 1993, Driscoll et al. 1984, Lesica and DeVelice 1992

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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