The system covers much of the eastern two-thirds of Montana, occurring continuously for hundreds of square kilometers, interrupted only by wetland/riparian areas or sand prairies. Soils are primarily fine and medium-textured. The growing season averages 115 days, ranging from 100 days on the Canadian border to 130 days on the Wyoming border. Climate is typical of mid-continental regions with long severe winters and hot summers. Grasses typically comprise the greatest canopy cover, and western wheatgrass (Pascopyrum smithii) is usually dominant. Other species include thickspike wheatgrass (Elymus lanceolatus), green needlegrass (Nassella viridula), blue grama (Bouteloua gracilis), and needle and thread (Hesperostipa comata). Near the Canadian border in north-central Montana, this system grades into rough fescue (Festuca campestris) and Idaho fescue (Festuca idahoensis) grasslands. Remnants of shortbristle needle and thread (Hesperostipa curtiseta) dominated vegetation are found in northernmost Montana and North Dakota, and are associated with productive sites, now mostly converted to farmland. Forb diversity is typically high. In areas of southeastern and central Montana where sagebrush steppe borders the mixed grass prairie, common plant associations include Wyoming big sagebrush-western wheatgrass (Artemisia tridentata ssp. wyomingensis/ Pascopyrum smithii). Fire and grazing are the primary drivers of this system. Drought can also impact it, in general favoring the shortgrass component at the expense of the mid-height grasses. With intensive grazing, cool season exotics such as Kentucky bluegrass (Poa pratensis), smooth brome (Bromus inermis), and Japanese brome (Bromus japonicus) increase in dominance; both of these rhizomatous species have been shown to markedly decrease species diversity. Previously cultivated acres that have been re-vegetated with non-native plants have been transformed into associations such as Kentucky bluegrass (Poa pratensis)/western wheatgrass (Pascopyrum smithii) or into pure crested wheatgrass (Agropyron cristatum) stands.
Dynamic vegetative communities make up this diverse prairie ecosystem. Vegetation is a mixture of mid and short grasses, generally having an average height of 30 centimeters (12 inches). Throughout the Montana portion of this system, rhizomatous western wheatgrass is the dominant component, especially on finer-textured soils and where the moisture balance is favorable. It decreases under prolonged or grazing regimes. Grasses were typically used by large herbivores such as bison, but since European settlement, herbivores such as cattle and sheep have been the primary users of the vegetation.
Near the Canadian border and at higher elevations with greater precipitation, this system grades into grasslands dominated by rough fescue and Idaho fescue. These two tussock grasses are indicative of more mesic sites and characterize the Rocky Mountain Lower Montane, Foothill and Valley Grassland system. In areas of southeastern Montana where the sagebrush steppe lands border the mixed grass prairie, common plant associations include silver sagebrush /western wheatgrass. In these border regions, shrub-loving wildlife such as antelope, mule deer, and sage grouse are common. Previously cultivated acres may have been re-vegetated by non-native plants creating associations such as Kentucky bluegrass/western wheatgrassand pure stands of crested wheatgrass. Sites with a strong component of green needlegrass indicate a more favorable moisture balance, although this is one of the most palatable of the mid-grasses. Needle and thread is also an important component; it increases with coarser soil textures, or under heavy grazing at the expense of western wheatgrass. Extreme overgrazing can result in the loss of western wheatgrass from the system, followed by drastic reductions in needle and thread and ultimately, the dominance of blue grama, Sandberg’s bluegrass (Poa secunda), and prairie junegrass (Koeleria macrantha). Common forbs within this system include yarrow (Achillea millefolium), scarlet globemallow (Sphaeralcea coccinea), western sagewort, (Artemisia ludoviciana), boreal sagewort (Artemisia frigida), silver lupine (Lupinus argenteus), fuzzy beardtongue (Penstemon eriantherus), shining penstemon (Penstemon nitidus), prairie cinquefoil (Potentilla gracilis), Missouri goldenrod (Solidago missouriensis) anddalea (Dalea species). Shrub species may include western snowberry (Symphoricarpos occidentalis), serviceberry (Amelanchier alnifolia), shrubby cinquefoil (Dasiphora fruticosa), creeping juniper (Juniperus horizontalis), silver sage and Wyoming big sagebrush (Artemisia tridentata var. wyomingensis).
Historically, frequent indigenous anthropogenic fires and large numbers of migrating bison and other herbivores contributed to plant species and plant community diversity within this system. In the Northern Great Plains, pre-settlement fire frequency occurred at intervals ranging from 3 to 20 years (Umbanhowar, 1996). The elimination of bison and frequent fire intervals disrupted plant community dynamics, leading to a decrease in plant community diversity.
Communities associated with this ecological system are adapted to soils that may be dry throughout the growing season. They may also occur on shallow soils, particularly Entisols, with parent material and/or bedrock formation close to the surface. Plant communities occurring on Entisols may be drought tolerant, grazing resistant, and winter hardy. Deep-rooted communities are more generally associated with Mollisols. Typically, these communities are tolerant of managed grazing practices, moderate-intensity fires, and fallowed wheat-cropping practices. Prolonged, extreme drought is a major threat to this system, reducing the density and cover of short grasses by as much as 80 percent and the bunchgrasses and native forbs to almost zero (Albertson, 1937). During prolonged drought, native forbs are rapidly replaced by non-native invasive forbs. During the severe droughts of the 1930’s and 1950’s, basal area cover of grasses decreased from 80 to less than 10 percent under moderate grazing regimes in 3 to 5 years (Barbour and Billings, 2000). In short, the dynamics of species changes in this system is a function of climate, but the magnitude of these changes is greatly influenced by the intensity of grazing and fire frequency.
Restoration strategies for this system will depend on site condition; occurrences in good condition can be restored by re-introducing prescribed fires. Periodic prescribed fires in late spring can improve productivity, contribute to species diversity and prevent encroachment of shrub communities, especially Wyoming sagebrush. Prescribed fires and appropriate grazing practices are important restoration tools to improve mixed grass prairie production and contribute to plant community diversity.
Occurrences that are severely degraded, formerly cultivated or reseeded to non-native species will require a combination of restoration techniques to create suitable conditions for native species establishment and natural recruitment. Some restoration sites may require the reintroduction of native dominant grass and forb species. In the past, large areas of this system have been planted to non-native grasses such as crested wheatgrass and smooth brome for farmland reclamation and erosion control. This has resulted in decreased mixed grass prairie species diversity and a reduced ability of native species to colonize and compete on these disturbed, reclaimed sites. Site preparation will requirenoxious species eradication and control for at least 2 seasons before and after reseeding. Pre-restoration techniques are largely accomplished by a combination of fall burning, tilling and in some cases, herbicide applications and addition of nitrogen. Native seedling density has been shown to be 20 times greater when a combination of these techniques is used (Wilson and Gerry, 1994).
Site preparation should involve soil disking techniques that discourage uniform soils and seed beds. Feathering and smoothing topsoil may not be appropriate in rough fescue grassland. Uniform soils may benefit invasive species such as Kentucky bluegrass and smooth brome, while roughened conditions may inhibit their growth, allowing rough fescue and its associated grasses to establish more readily (Desserud, 2006). Increasing the intensity of tilling has increased native species density and establishment (Wilson and Gerry, 1994).
Barbour, Michael G. 2000. North American terrestrial vegetation. Cambridge: Cambridge University Press.
Desserud, Peggy Ann. 2006. Restoration of rough fescue grassland on pipelines in southwestern Alberta. Lethbridge, Alta: Alberta Sustainable Resource Development, Rangeland Management Branch, Public Lands and Forests Division.
Erickson, Albert W, and D B. Siniff. A Statistical Evaluation of Factors Influencing Aerial Survey Results on Brown Bears. Anchorage, Alaska: Alaska Department of Fish and Game, 1963. Print.
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