Montana Field Guide

This is a minor grassland group in Montana occurring in the relatively high elevation basins, valley bottoms and the lower foothills of the Bighorn/Wyoming Basin, and potentially in extreme southwest MT (Beaverhead County) and also near Gardiner in southern Park County. These arid grasslands are composed of drought-tolerant perennial bunchgrasses such as Needlegrasses (Stipa spp.), Blue Grama (Bouteloua gracilis), Sand Dropseed (Sporobolus cryptandrus), Sandberg’s Bluegrass (Poa secunda), and Bluebunch Wheatgrass (Elymus spicatus). Scattered shrubs and subshrubs, such as Wyoming Big Sagebrush (Artemisia tridentata ssp wyomingensis, Saltbush (Atriplex spp.), Broom Snakeweed (Gutierrezia sarothrae), and Winterfat (Krascheninnikovia lanata) are often present. These grasslands are only marginally different from those of G273 Rocky Mountain Low Elevation - Dry Grassland as they overlap extensively in species’ composition. However, they generally occur in more arid sites and are more limited in geographic distribution in the state. Substrates are often well-drained sandy or loam soils derived from sedimentary parent materials but are quite variable and may include fine-textured soils derived from igneous and metamorphic rocks.

This Group does not have a similar Ecological System representative in Montana. The most similar communities include some of the driest communities within the Rocky Mountain Lower Montane, Foothill, and Valley Grassland Ecological System.

Semi-arid to Arid Grasslands; Intermountain Region

Typical Dominants: Indian Ricegrass (Oryzopsis hymenoides), Blue Grama (Bouteloua gracilis), Needle-and-Thread (Stipa comata), Sandberg’s Bluegrass (Poa secunda), and Bluebunch Wheatgrass (Elymus spicatus)

This grassland group is a minor type in MT, occurring in valley bottoms and lower foothills of the Bighorn/Wyoming Basin, and potentially in extreme southwest MT (Beaverhead County) and also near Gardiner in southern Park County.

In Montana, G311 occurs or potentially occurs in Level IV Ecoregions: 17m (Dry Mid-elevation Sedimentary Mountains of the Middle Rockies), 18b (Bighorn Basin), 43v (Pryor-Bighorn Foothills of the Northwestern Great Plains); and 17aa (Dry Intermontane Sagebrush Valleys).

In Montana, G311 occurs or potentially occurs within these Major Land Resource Areas: 32 - Northern Intermountain Desertic Basins; southern part of 46 - Northern and Central Rocky Mountain Foothills and 44B - Central Rocky Mountain Valleys.

Large Patch

These arid grasslands occur in the relatively high-elevations basins, valley bottoms and foothills of southern Montana from 4,500-6,500 feet in elevation. They occur on flat to gently sloping terrain and on steep slopes primarily on warmer, southerly slopes. This group experiences cold temperate conditions with hot summers and cold winters. Annual precipitation is usually from 8-15 inches. A significant portion of the precipitation falls in the summer months during convective storms with the remainder falling during the winter and early spring months. Soils supporting this group vary from shallow to deep, and from sandy to finer-textured loams. They are generally well-drained soils derived from sedimentary parent materials, commonly sandstones and shales but are quite variable and may include fine-textured soils derived from igneous and metamorphic rocks. Some occurrences have a high cover of cryptogams on the soil surface, which tends to increase the stability of the soils during torrential summer rains and heavy windstorms (Kleiner and Harper 1977).

These arid grasslands are dominated by cool and warm-season, perennial bunchgrasses with cover that is sparse to moderately dense. Cool season grasses include Indian Ricegrass (Oryzopsis hymenoides), Needle-and-Thread (Stipa comata), Nelson’s Needlegrass (Stipa nelsonii), Sandberg’s Bluegrass (Poa secunda) and Bluebunch Wheatgrass (Elymus spicatus). Common warm season grasses include Blue Grama (Bouteloua gracilis), Sand Dropseed (Sporobolus cryptandrus) and Purple Three-awn Grass (Aristida purpurea). Scattered shrubs and dwarf-shrubs often are present, especially Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis), Saltbush (Atriplex spp.), Broom Snakeweed (Gutierrezia sarothrae), and Winterfat (Krascheninnikovia lanata). Forb cover is generally sparse but can be relatively diverse. Common forbs are Gaura coccinea, Arrowleaf Balsamroot (Balsamorhiza sagittata), Hymenopappus filifolius, Machaeranthera canescens, Sphaeralcea coccinea, Lappula occidentalis, Lithophragma glabrum, Lupinus pusillus, Opuntia polyacantha, Plantago patagonica, Pediomelum argophyllum, Artemisia campestris, Artemisia dracunculus, Artemisia ludoviciana, and species of Antennaria, Astragalus, Cryptantha, Eriogonum, Gilia, and Lappula. Cryptogams are abundant at some sites. Exotic species such as Bromus tectorum, Draba verna, Lactuca serriola, Salsola tragus, Kochia scoparia, Poa pratensis, Sisymbrium altissimum, and Tragopogon dubius are often present.

In Montana, this group is represented by 3 Alliances and 4 Associations within the National Vegetation Classification. These likely cover most, if not all, the range in vegetation communities present within this group in the state.

Improperly managed livestock grazing may increase soil erosion, decrease cover of palatable plant species in these arid grasslands and increase weedy species (USDA 1937). Annual bromes are problematic weeds in these arid grassland settings, resulting in abundant fine fuels when cured that carry fire and increase the frequency of fires (FEIS 1998).

M.E. Hall and M.S. Reid 2015

S. Mincemoyer

12/4/2024