Montana Valley and foothill grasslands
The Montana Valley and Foothill Grasslands biome spans approximately 9,300 square miles across Montana in the U.S. and Alberta in Canada, situated at altitudes of 1,800 to 5,400 feet. This ecosystem features a diverse climate, with cool and dry conditions interspersed with microclimates that can either capture or lose precipitation, significantly impacting its rich biological diversity. The grasslands are characterized by various plant species, including fescue at higher elevations, bluebunch on steep slopes, and western wheatgrass on lower slopes, alongside shrubs and trees such as Douglas fir and ponderosa pine.
Wildlife in these grasslands has historically included large herbivores, although populations of species like the American bison are now limited. The grizzly bear is a prominent mammal in the area, alongside other species such as white-tailed deer and pronghorn antelope. The biome faces numerous challenges, including habitat loss due to urban development, agriculture, and environmental pressures like climate change, which threaten its ecological integrity. Conservation efforts exist in various protected areas to preserve the remaining natural habitat, highlighting the importance of this unique ecosystem.
Subject Terms
Montana Valley and foothill grasslands
Category: Grassland, Tundra, and Human Biomes.
Geographic Location: North America.
Summary: In addition to the unique biodiversity it harbors, this biome is vital because its valleys provide habitat connectivity across the foothills of the Rocky Mountains.
Located in Montana in the United States and Alberta in Canada, the Montana Valley and Foothill Grasslands biome runs along the foothills and high valleys of the central Rocky Mountains. The ecosystem covers some 9,300 square miles (24,000 square kilometers), and ranges between 1,800 and 5,400 feet (550 and 1,650 meters) in altitude. The grasslands extends from the uppermost flatland reaches of the Missouri River watershed on the Rocky Mountain Front, into the Clark Fork-Bitterroot catchment of the Columbia River system within Montana and parts of Idaho; and in Alberta, along the Oldman, Little Bow, and Bow Rivers, as well as other tributaries of the Peace and Athabasca Rivers.
Climate, Topography, and Vegetation
The climate in the Montana Valley and Foothill Grasslands biome is generally cool and dry. However, there is a mix of moisture microclimates here, with one major factor being the shape, orientation, and elevation of the valleys as they either capture, deflect, or are themselves deprived of precipitation that arrives mainly from the prevailing Pacific Ocean-generated Chinook wind pattern. There are valleys and foothills in the rain shadow, where semiarid conditions maintain; others effectively capture moisture and have habitats that make good use of rainfall. Most areas experience seasonal runoff from snowmelt. The result is broad biological diversity.
Riparian corridors are important because they allow the passage of species across valley bottoms, opening critical habitat linkages for plant and especially animal types between separate mountain ranges. The stream beds and rivers are also key corridors for species that descend seasonally from sheltering elevations; specifically, the wet and high-productivity valleys represent ideal sites for the grizzly bear (Ursus arctos) on its path to annual recolonization of the grassland habitats.
Overall, the mean annual temperature across this biome is 26 degrees F (3.5 degrees C). The summer mean is 57 degrees F (14 degrees C); winter mean hovers at a frosty 18 degrees F (minus 8 degrees C). Mean annual precipitation is approximately 17 inches (425 millimeters).
The dominant grass species here include fescue (Festuca spp.) at higher and wetter elevations, interspersed with bluebunch (Pseudoroegneria spicata) on very steep slopes. Western wheatgrass (Pascopyrum smithii) is most abundant on lower slopes. Mixed in are likely to be such shrubs as creeping juniper (Juniperus horizontalis), shrubby cinquefoil (Dasiphora floribunda), and kinnikinnik (Arctostaphylos uva-ursi). Sagebrush (Artemisia spp.) is a dominant species in many of the semiarid swaths.
While the grasslands are ubiquitous across the drier zones here, shrubland habitat is often seen in niches of higher water availability. Closest to the riparian corridors are found considerable stands of Douglas fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa).
At elevations above the limits of the grassland, forests of quaking aspen (Populus tremuloides) and woodlands of limber pine (Pinus flexilis) are common, often with an understory cover of chokeberry (Prunus virginiana), Woods’s rose (Rosa woodsii), or Saskatoon serviceberry (Amelanchier alnifolia). Below the grassland, where wetter conditions tend to prevail, are often found stands of willow (Salix spp.) and red-osier dogwood (Cornus sericea).
Fauna
The traditional wildlife of this biome once included the remarkably vast herds of the American bison (Bison bison), the elk (Cervus canadensis) and the bighorn shell (Ovis canadensis); the populations of each remain in small numbers. The most iconic mammal today is the grizzly bear, which makes its seasonal descent from the mountainsides in warmer months to forage along the rivers and in grassland habitats. Characteristic species here include white-tailed deer (Odocoilecus virginianus), pronghorn antelope (Antilocapra americana), coyote (Canis latrans), mountain cottontail (Sylvilagus nuttallii), red-tailed hawk (Buteo jamaicensis), and dusky grouse (Dendragapus obscurus).
The Montana Valley and Foothill Grasslands biome supports some fish species and sub-species that are endemic, meaning found nowhere else, or near-endemic. These include the west slope cutthroat trout (Oncorhynchus clarkii lewisi), Yellowstone cutthroat (Oncorhynchus clarkii bouvieri), and the fluvial arctic grayling (Thymallus arcticus), a relict fish species still present from the last glaciation.
The reptile suite features prairie rattlesnake (Crotalus viridis), western skink (Eumeces skitonianus), and greater short-horned lizard (Phyrnosoma hernandesi). The plains spadefoot (Spea bombifrons), boreal chorus frog (Pseudacris maculata), and barred salamander (Ambystoma mavortium) are among the most frequently noted amphibians here.
Human Impact
Historically, the heavy grazing by native, free-ranging herbivores such as buffalo was a continuous influence on the grasslands ecosystem here. This changed rapidly to more intensive stock grazing by domesticated fauna. Draining the wetland areas downhill from the grasslands has been a common practice as the land has attracted more human settlements, with conversion of grasslands to row crops, in effect replacing native species with exotic grasses. Such practices have also opened the door to noxious weed invasion.
The biome is considered a critical one, and generally thought of as in an endangered status, with approximately one-fourth of its area remaining as relatively original, intact habitat, mainly along the East Front of the Rockies from Great Falls, Montana, to near Calgary, Alberta. The most prevalent current threat is the conversion of surviving native habitats into urban and semi-urban areas, which sharply reduces the habitat connectivity for wildlife species. Building projects are concentrated in the Paradise Valley on the Yellowstone River, in the Bitterroot Valley, and in the Gallatin River Valley. Another ongoing threat is groundwater pollution from several Superfund toxic waste sites and various large mining and expanding hydrocarbon drilling operations.
About one-quarter of its area is protected under various conservation schemes; these include the National Bison Range, Pine Butte Swamp, and Red Rock Lakes National Wildlife Refuge in Montana; and in Canada, Banff National Park and Fish Creek Provincial Park, the landmark large urban natural preserve in Calgary.
Lower rainfall, higher temperatures, and more damage from wildfires are among the projected impacts of climate change to the Montana Valley and Foothill Grasslands biome. The results of such trends could include a gradual loss of grasslands to encroaching woodlands and forest—or the opposite could occur, with grasslands mounting somewhat higher elevations as the trees give way.
Interactions at the forest-grassland ecotone (overlap area) are quite complex, and are further complicated by animal behavior, both wild and domestic. Livestock grazing patterns, for example, will be a factor, as many herd animals are quite effective at eradicating young tree shoots along forest fringe areas. During warmer periods in the past, some trees, such as larch, have tended to regenerate faster, and to more successfully move downhill, colonizing areas of grassland.
Certain species adapt by migration far more easily than others to temperature changes in their habitats. Research has shown, for example, that the long-tailed vole, happiest in aspen forests here, will readily move downhill into nearby grassland habitat when such areas are vacated by their montane vole rivals. The montane vole, on the other hand, has shown little if any propensity for moving uphill into the forest zone when the long-tailed vole moves out, and when warming temperatures or other factors make its own grassland habitat untenable.
Bibliography
Foresman, Kerry R. and Alexander V. Badyaev. Mammals of Montana. Missoula, MT: Mountain Press Publishing, 2012.
Kudray, Gregory M. and Stephen V. Cooper. Montana’s Rocky Mountain Front: Vegetation Map and Type Description. Helena: Montana Natural Heritage Program and U.S. Fish and Wildlife Service, 2006.
Restani, Marco. “Resource Partitioning Among Three Buteo Species in the Centennial Valley, Montana.” The Condor 93, no. 4 (1991).
Vance, Linda K. and Tara Luna. “Montana Field Guide—Rocky Mountain Lower Montane, Foothill, and Valley Grassland.” Montana Natural Heritage Program. http://fieldguide.mt.gov/displayES‗Detail.aspx?ES=7112.