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Community Field Guide

Scientific Name:
Pascopyrum smithii - Bouteloua gracilis - Carex filifolia Herbaceous Vegetation

Common Name:
Western wheatgrass - blue grama - threadleaf sedge Herbaceous Vegetation


Photo by Bonnie Heidel

Community Description

Summary:
This western wheatgrass prairie community occurs throughout much of the northwestern Great Plains of the United States and Canada, on flat or gently sloping terrain. Many stands are on floodplains or gentle valley slopes. Some are on uplands. The soils are clay loam, silt loam, or loam and usually deep and fertile. This community is dominated by medium and short graminoids. The midgrass stratum is dominated by Pascopyrum smithii or Elymus lanceolatus. Common associates include Koeleria macrantha, Hesperostipa comata (= Stipa comata), and Nassella viridula. Hesperostipa comata is more common on the upper slopes and drier upland sites with sandier soils, whereas Nassella viridula is more common on the lower slopes and floodplains with finer-textured soils. The most common short graminoid is Bouteloua gracilis. Other common graminoids include Carex filifolia, Carex inops ssp. heliophila, Carex duriuscula (= Carex eleocharis), and Carex pensylvanica. Forbs do not contribute much of the canopy cover but they are scattered throughout this community. Typical forbs are Tragopogon dubius, Gaura coccinea, Hedeoma hispida, Phlox hoodii and Sphaeralcea coccinea.

In Montana, this association occurs as a prevalent plant association across eastern plains landscapes and at all smaller scales on fine-textured soils. It has Pascopyrum smithii composing a significant portion of the canopy cover, representing mid-height stature and rhizomatous growth form, unless suppressed under drought cycles. Short stature graminoids (grasses and sedges) compose equal or greater cover than the canopy of mid-height grasses.

Environment:
This community is found on flat or gently sloping terrain. Many stands are on floodplains or gentle valley slopes, others are on uplands. Surface layers of soils are usually clay loams, although stands of this type may also be found on loams, silt loams, silty clays and clays (Hanson and Whitman 1938, Hansen and Hoffman 1988). In Alberta and Saskatchewan this association grows on solonetzic soils (with an eluvial horizon above a dense clay horizon high in sodium salts) developed on thin glacial till over Cretaceous shale (Coupland 1961). This community does not appear to be found in mountain valleys (Hanson and Dahl 1956, Jones 1992).

In Montana, this community occurs on deep-soil settings of the plains on loams, silt loams, and clay loams, with or without impeded drainage. It spans the full range of topographic positions in its current vegetation definition, while sorting by topographic position and permeability depending on species dominance phase. This association and the Hesperostipa comata - Bouteloua gracilis - Carex filifolia Association (CEGL002037) could be considered the most common plant associations in the Northern Great Plains (Martin et al. 1998). These two associations, cited by many authors as the climatic climax communities for this region, are manifested by matrix or large patch occurrences frequently found dominating whole landscapes. The Hesperostipa comata defined community is more associated with uplands and the Pascopyrum smithii defined type characterizes sites with higher moisture status, generally occurring at lower positions in the landscape. In Powder River County, the association occurs on gentle slopes ranging from 0-35 % and it is characteristic of the widespread Silty Ecological Site of the 10-14 inch precipitation zone. It is prevalent on gentler slopes within the Elso-Midway-Thurlow and the Elso-Remmit-Ocean Lake soil associations derived from calcareous shales. It also occurs on Silty Ecological Sites on well-drained deep-loam soils of the Elso Ocean Lake association to the north. It is occasional on upland and bench positions with suitable substrate in the Ringling-Cabba-Midway association to the west, a Clayey Ecological Site of the 15-19 inch precipitation zone.

Vegetation:
This community is dominated by medium and short graminoids. Total vegetation cover is usually high (Hanson and Dahl 1956, Hansen et al. 1984). Pascopyrum smithii or Elymus lanceolatus or both (the two species are similar both morphologically and ecologically) and Bouteloua gracilis usually contribute the most cover; however, Bouteloua gracilis cover may vary from codominant to locally absent. Carex filifolia, Carex duriuscula (= Carex eleocharis), and Carex pensylvanica are often secondary species, but they also vary from moderate cover to locally absent. Hesperostipa comata (= Stipa comata) usually is present as a secondary species, but it often codominates on sandy loam soils. In Alberta and Saskatchewan, Hesperostipa curtiseta (= Stipa spartea var. curtiseta) may be as common as Hesperostipa comata. Koeleria macrantha is present in most stands and may contribute substantial cover. The forbs most likely to be found in this association are Phlox hoodii, Sphaeralcea coccinea, Polygonum ramosissimum, Plantago patagonica, Opuntia polyacantha, Artemisia frigida, Antennaria microphylla, and Hedeoma hispida. In southeastern Montana, western North Dakota, and northeastern Wyoming, stands of this association often contain Artemisia tridentata ssp. wyomingensis. Exotic brome grasses, especially Bromus commutatus and Bromus tectorum, are present in many stands of this association and they commonly contribute substantial cover (Hanson and Dahl 1956, Coupland 1961, Hansen et al. 1984, Hansen and Hoffman 1988).

We note that in Powder River County, all combinations of species as co-dominants have been documented.Buchloe dactyloides is also a recurring co-dominant to add to the plant association description. In places co-dominated by Pascopyrum smithii and Buchloe dactyloides, the cover of grasses was high under good range conditions (greater than 70%) and the cover of forbs was low, often including one or more of the following: Agoseris glauca, Hedeoma hispida, Lomatium foeniculaceum , Linum australe , Psoralea argophylla , and Sphaeralcea coccinea . Under degraded range conditions, the cover of annual bromes, Vulpia octoflora and Poa secunda increased, and the cover of Pascopyrum smithii decreased. Forb cover was significant only under degraded conditions, with such non-native or increaser species as Alyssum desertorum , Camelina sativa , Opuntia polyacantha and Plantago eriopoda . In the course of this study, we took ten plots and extensive field notes, with particular emphasis on documenting the vegetation co-dominated by Pascopyrum smithii and Buchloe dactyloides that was extensive on BLM lands.

Range:
This western wheatgrass prairie community occurs throughout much of the northwestern Great Plains of the United States and Canada on flat or gently sloping terrain, ranging from Alberta and Saskatchewan in Canada south to Nebraska and possibly Colorado.

Dynamics:
In the past, fire likely occurred commonly in this type. Vast (singly and in the aggregate) prairie dog (Cynomys ludovicianus) "towns" once developed on the favorable substrates of this type and exploited its vegetation. Prairie dog populations have undergone a precipitous decline since settlement, so much of this type could be in various states of secondary succession, returning from a somewhat denuded state and altered composition created by the prairie dogs (and attendant bison that found nutritious forage here). Fire, both aboriginal- and lightening-caused, was a regular part of this landscape. Fire-return intervals have been considerably lengthened since settlement by European-Americans.

Global Rank: G4 State Rank: S4

Global Rank Comments:
The G4 rank is based on the broad geographic range of this type, and its status as a common vegetation type within that range. Heavy grazing and lack of fire throughout its range may cause many stands to have a high proportion of exotics.

Community References

Identifier:
CEGL001579

Author:
H.C. Hanson and W. Whitman, mod. J. Drake and D. Faber-Langendoen (mod. B. Heidel)

Citations:
Bourgeron and Engelking 1994, Driscoll et al. 1984, Ellison and Woolfolk 1937, Hansen 1985, Hansen and Hoffman 1988, Hansen et al. 1984, Hanson and Dahl 1956, Hanson and Whitman 1938, Johnston 1987, Jones 1992b, Ode pers. comm., Steinauer and Rolfsmeier 2000, Weaver and Albertson 1956

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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