Montana Field Guide

Dry Mixedgrass Prairie is the dominant grassland group across the prairie region in Montana. It is characterized by sparse to dense cover of various short to mid-statured, perennial grasses. Some sites within this group support a short or dwarf-shrub component with a layer of grasses. Dominant species include the following cool season grasses; Needle-and-Thread (Stipa comata), Western Wheatgrass (Elymus smithii), Bluebunch Wheatgrass (Elymus spicatus), Thickspike Wheatgrass (Elymus lanceolatus) and Prairie Junegrass (Koeleria macrantha) Blue Grama (Bouteloua gracilis) and Little Bluestem (Schizachyrium scoparium) are common warm-season grass at some sites. Upland sedges, such as Carex inops ssp. heliophila and Carex filifolia, are important components of some sites. Short and dwarf-shrubs are common components of some mixedgrass prairie communities and as a result, the Dry Mixedgrass Prairies transition readily into shrub-steppe communities of G302 and G310 as well as some Badlands and Sparsely-Vegetated communities. More mesic grassland sites are part of the much less common G141 - Great Plains Mesic Mixedgrass Prairie while sandy sites are part of G889 - Great Plains Sand Prairie. This group is separated from G141 - Great Plains Mixedgrass Prairie Group based on soil moisture and species composition. Stronger constancy and dominance of the short and mid grasses, distinguish this type from the related mesic mixedgrass types. Strong grazing pressures on mesic mixedgrass prairies, which increases the shortgrass component, can blur the distinction between the two types.

This Group includes the majority of the Great Plains Mixedgrass Prairie Ecological System excluding the more mesic communities.

Shortgrass Prairie; Warm and Cool Season Grasses; Graminoids >25% Cover; Great Plains Region

Typical Dominants: Little Bluestem (Schizachyrium scoparium), Blue Grama (Bouteloua gracilis) Needle-and-Thread (Stipa comata), Prairie Junegrass (Koeleria macrantha), Western Wheatgrass (Elymus smithii), Thickspike Wheatgrass (Elymus lanceolatus), Bluebunch Wheatgrass (Elymus spicatus), Carex filifolia and Carex inops ssp. heliophila

This Group occurs in the Great Plains of central and eastern Montana extending west to the foothills of the Rocky Mountains. It is the dominant grassland type across the plains and prairie region.

In Montana, G331 occurs in Level III Ecoregions: 42 (Northwestern Glaciated Plains) and 43 (Northwestern Great Plains).

In Montana, G331 occurs or potentially occurs within these Major Land Resource Areas: 46 Northern and Central Rocky Mountain Foothills, 52 - Brown Glaciated Plains; 53A - Northern Dark Brown Glaciated Plains; 53B - Central Dark Brown Glaciated Plains; 54 - Rolling Soft Shale Plain, 58A,B,C,D - Northern Rolling High Plains, 60A,B - Pierre Shale Plains.

Matrix

This type is generally found in a semi-arid climate with cold winters and hot summer temperatures. Precipitation is most abundant during convective summer storms along with winter snowfall and spring rains. Sites occur primarily on flat to rolling topography with some low-relief hummocky areas. Surficial materials are predominantly glacial till to the north of the Missouri River, with some glacio-lacustrine areas. Glacio-fluvial sediments are common along major river valleys, and eolian materials are prevalent in some areas (Adams et al. 2013). Predominant soils are deep and well-drained to imperfectly drained, and have a thick, dark A horizon. Textures range from loam to sandy loam. Significant areas of Solonetzic soils, characterized by a subsoil hardpan layer with a high proportion of sodium can be found in some areas (Adams et al. 2013).

The vegetation of this group is characterized by a sparse to dense cover of various short to mid-statured, perennial grasses. Both bunchgrasses and rhizomatous grasses are represented, and sites may be dominated by one or the other or contain a mix of both types. Some sites within this group support a short or dwarf-shrub component with a layer of grasses. Dominant species include the following cool season grasses; Needle-and-Thread (Stipa comata), Western Wheatgrass (Elymus smithii), Bluebunch Wheatgrass (Elymus spicatus), Thickspike Wheatgrass (Elymus lanceolatus) and Prairie Junegrass (Koeleria macrantha) Blue Grama (Bouteloua gracilis) and Little Bluestem (Schizachyrium scoparium) are common warm-season grass at some sites. Upland sedges, such as Carex inops ssp. heliophila and Carex filifolia, are important components of some sites. Short and dwarf-shrubs are common components of some mixedgrass prairie communities, including Skunkbush Sumac (Rhus trilobata), Creeping Juniper (Juniperus horizontalis), Rubber Rabbitbrush (Ericameria nauseosa), Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis), Gardner’s Saltbush (Atriplex gardneri), and Winterfat (Krascheninnikovia lanata). The Plains Pricklypear (Opuntia polyacantha) is a common component of this group. Forbs may be sparsely to moderately represented and the diversity can vary widely across the type.

As currently defined, this group includes 6 Alliances and 18 Associations within the National Vegetation Classification in Montana. However, A2302 - Artemisia tridentata/Pascopyrum smithii Shrub Grassland Alliance and its 2 Associations appear to be better placed into G302 - Intermountain Basins Big Sagebrush Steppe with other Wyoming Big Sagebrush Shrub Steppe communities. Additionally, CEGL001330 - Ericameria nauseosa/Pseudoroegneria spicata Shrubland appears to be better placed with G310 - Rabbitbrush - Arid Steppe and Shrubland.

Fire, drought, and grazing constitute the primary dynamics affecting this group (Adams et al. 2013).

Western Wheatgrass and Thickspike Wheatgrass will decline in abundance with grazing pressure, while Blue Grama and Prairie Junegrass cover increases on degraded sites.

See Adams et al. (2013) for a discussion of the recovery of dry mixedgrass prairie following cultivation and abandonment.

S. Menard, L. Allen and J. Drake 2015

S. Mincemoyer

12/4/2024