Northern Rockies Foothill and Valley Grassland

This ecological system of the northern Rocky Mountains is found at lower montane to foothill elevations in the mountains and large valleys of northeastern Wyoming and western Montana, west through Idaho into the Blue Mountains of Oregon, and north into the Okanagan and Fraser plateaus of British Columbia and the Canadian Rockies. They also occur to the east in the central Montana mountain "islands," foothills, as well as the Rocky Mountain Front and Big and Little Belt ranges. These grasslands are floristically similar to Inter-Mountain Basins Big Sagebrush Steppe (CES304.778), Columbia Basin Foothill and Canyon Dry Grassland (CES304.993), and Columbia Basin Palouse Prairie (CES304.792), but are defined by shorter summers, colder winters, and young soils derived from recent glacial and alluvial material. These grasslands reflect a shift in the precipitation regime from summer monsoons and cold snowy winters found in the Southern Rockies to predominantly dry summers and winter precipitation. In the eastern portion of its range in Montana, winter precipitation is replaced by a spring peak in precipitation. They are found at elevations from 300 to 1650 m, ranging from small meadows to large open parks surrounded by conifers in the lower montane, to extensive foothill and valley grasslands below the lower treeline. In the southern extent, some of these valleys may have been primarily sage-steppe with patches of grassland in the past, but because of land-use history post-settlement (herbicide, grazing, fire, pasturing, etc.), they have been converted to grassland-dominated areas. Soils are relatively deep, fine-textured, often with coarse fragments, and non-saline, often with a microphytic crust. The most important species are cool-season perennial bunchgrasses and forbs (>25% cover), sometimes with a sparse (<10% cover) shrub layer. Pseudoroegneria spicata, Festuca campestris, Festuca idahoensis, or Hesperostipa comata commonly dominate sites on all aspects of level to moderate slopes and on certain steep slopes with a variety of other grasses, such as Achnatherum hymenoides, Achnatherum richardsonii, Hesperostipa curtiseta, Koeleria macrantha, Leymus cinereus, Elymus trachycaulus, Bromus inermis var. pumpellianus, Achnatherum occidentale, Pascopyrum smithii, and other graminoids such as Carex filifolia and Danthonia intermedia. Other grassland species include Opuntia fragilis, Artemisia frigida, Carex petasata, Antennaria spp., and Selaginella densa. Important exotic grasses include Phleum pratense, Bromus inermis, and Poa pratensis. Shrub species may be scattered, including Amelanchier alnifolia, Rosa spp., Symphoricarpos spp., Juniperus communis, Artemisia tridentata, and in Wyoming Artemisia tripartita ssp. rupicola. Common associated forbs include Geum triflorum, Galium boreale, Campanula rotundifolia, Antennaria microphylla, Geranium viscosissimum, and Potentilla gracilis. A soil crust of lichen covers almost all open soil between clumps of grasses; Cladonia and Peltigera are the most common lichens. Unvegetated mineral soil is commonly found between clumps of grass and the lichen cover. The fire regime of this ecological system maintains a grassland due to rapid fire return that retards shrub invasion or landscape isolation and fragmentation that limits seed dispersal of native shrub species. Fire frequency is variable but is presumed to be generally less than 20 years to reduce shrub cover and maintain grassland. These are extensive grasslands, not grass-dominated patches within the sagebrush shrub-steppe ecological system. Festuca campestris is easily eliminated by grazing and does not occur in all areas of this system.

The most important species are cool-season perennial bunchgrasses and forbs (>25% cover), sometimes with a sparse (<10% cover) shrub layer. Pseudoroegneria spicata, Festuca campestris, Festuca idahoensis, or Hesperostipa comata commonly dominate sites on all aspects of level to moderate slopes and on certain steep slopes with a variety of other grasses, such as Achnatherum hymenoides, Achnatherum richardsonii, Hesperostipa curtiseta, Koeleria macrantha, Leymus cinereus, Elymus trachycaulus, Bromus inermis var. pumpellianus (= Bromus pumpellianus), Achnatherum occidentale (= Stipa occidentalis), Pascopyrum smithii, and other graminoids such as Carex filifolia and Danthonia intermedia. Other grassland species include Opuntia fragilis, Artemisia frigida, Carex petasata, Antennaria spp., and Selaginella densa. Important exotic grasses include Phleum pratense, Bromus inermis, and Poa pratensis. Shrub species may be scattered, including Amelanchier alnifolia, Rosa spp., Symphoricarpos spp., Juniperus communis, Artemisia tridentata, and in Wyoming Artemisia tripartita ssp. rupicola. Common associated forbs include Geum triflorum, Galium boreale, Campanula rotundifolia, Antennaria microphylla, Geranium viscosissimum, and Potentilla gracilis. A soil crust of lichen covers almost all open soil between clumps of grasses; Cladonia and Peltigera are the most common lichens. Unvegetated mineral soil is commonly found between clumps of grass and the lichen cover.

This system is found at lower montane to foothill elevations in the mountains and large valleys of northeastern Wyoming and western Montana, west through Idaho into the Blue Mountains of Oregon, and north into the Okanagan and Fraser plateaus of British Columbia and the Canadian Rockies. They also occur to the east in the central Montana mountain "islands" and foothills, as well as the Rocky Mountain Front Range and Big and Little Belt ranges. These grasslands are floristically similar to Inter-Mountain Basins Big Sagebrush Steppe (CES304.778), Columbia Basin Foothill and Canyon Dry Grassland (CES304.993), and Columbia Basin Palouse Prairie (CES304.792), but are defined by shorter summers, colder winters, and young soils derived from recent glacial and alluvial material. These lower montane and valley grasslands represent a shift in the precipitation regime from summer monsoons and cold snowy winters found in the Southern Rockies to predominantly dry summers and winter precipitation. In the eastern portion of its range in Montana, winter precipitation is replaced by a huge spring peak in precipitation. They are found at elevations from 300 to 1650 m, ranging from small meadows to large open parks surrounded by conifers in the lower montane, to extensive foothill and valley grasslands below the lower treeline. In the southern extent some of these valleys may have been primarily sage-steppe with patches of grassland in the past, but because of land-use history post-settlement (herbicide, grazing, altered fire regime, pasturing, etc.), they have been converted to grassland-dominated areas. Soils are relatively deep, fine-textured, often with coarse fragments, and non-saline, often with a microphytic crust.

These are extensive grasslands, not grass-dominated patches within the sagebrush shrub-steppe ecological system. Festuca campestris is easily eliminated by grazing and does not occur in all areas of this system. The most droughty sites produce little and discontinuous fuel and likely have much longer fire regimes. Isolation of grassland patches by fragmentation may also limit seed dispersal of native shrubs leading to persistence of the grassland. Soil drought and herbivory retard shrub and tree invasion resulting in a patchy distribution of shrubs and trees when present.

The high-frequency fire regime of this ecological system maintains a grassland due to rapid fire return that retards shrub invasion or landscape isolation and fragmentation that limits seed dispersal of native shrub species. Fire frequency is presumed to be less than 20 years generally. Johnson and Swanson (2005) presumed fire frequency to be less than 35 years in the Blue and Ochoco mountains of Oregon. Wikeem and Wikeem (2004) compiled average fire intervals for interior grasslands in British Columbia which range from 5-20 years. Klenner et al. (2008) research supports a fire regime of predominantly mixed-severity fires that maintain grasslands in the dry forest and grasslands ecotone in the southern interior of British Columbia.

Biological soil crust cover is important in these grasslands. It alters the composition of perennial species and increases the establishment of native disturbance-increasers and annual grasses, particularly Bromus tectorum and other exotic annual bromes (WNHP 2011). Crust cover and diversity are greatest where not impacted by trampling, other soil surface disturbance and fragmentation (Belnap et al. 2001, Rosentreter and Eldridge 2002, Tyler 2006).

LANDFIRE developed a state-and-transition vegetation dynamics VDDT model for this system which has three classes in total (LANDFIRE 2007a, BpS 1911390). These are summarized as:

A) Early Development 1 All Structures (5% of type in this stage): Graminoid cover is 0-10%. Post-fire, early-seral community dominated by bunchgrasses and forbs. Herbs and forbs will generally have higher cover than pre-burn and may include milkvetch, balsamroot, lupine, yarrow and prairie junegrass. Cover ranges from 0-10%. In the absence of fire or heavy animal impact, this condition succeeds to a mid-development condition (class B). Age ranges from 0-2 years. Idaho fescue may be present but will recover more slowly than the bluebunch wheatgrass after fire.

B) Mid Development 1 Closed (25% of type in this stage): Graminoid cover is 11-30%. Mid-development with moderate canopy closure dominated by bunchgrasses with forb cover generally higher than pre-burn. Typically lasts 5 years.

C) Late Development 1 Closed (70% of type in this stage): Tree cover is 31-100%. Late-development, closed canopy of grasses and forbs. Bunchgrasses dominate with low densities of shrubs (<10%) in some areas, particularly where this BpS transitions to shrub- or tree-dominated communities. Shrub species may include big sagebrush, buckwheat, ceanothus, bitterbrush and snowberry.

This type has frequent replacement fires (fire regime group II). Most species in this type are fire-adapted and respond favorably to these fire types. Where these systems occur within forested ecosystems, fire frequency will be strongly influenced by the surrounding forest's fire regime (e.g., 10-20 years). Where these systems occur below lower treeline, fire frequencies may be longer (e.g., 20-30 years) (LANDFIRE 2007a, BpS 1911390).

The primary land uses that alter the natural processes of the system are associated with livestock practices, exotic species, fire regime alteration, direct soil surface disturbance, and fragmentation (WNHP 2011). Excessive grazing stresses the system through soil disturbance increasing the probability of establishment of native disturbance-increasers and annual grasses, particularly exotic annual bromes (Bromus racemosus, Bromus arvensis, Bromus hordeaceus, Bromus tectorum) and Ventenata dubia on more xeric sites and exotic perennial grasses Bromus inermis, Phleum pratense, and Poa pratensis on more mesic sites (WNHP 2011). Other exotic species threatening this ecological system through invasion and potential complete replacement of native species include Hypericum perforatum, Potentilla recta, Euphorbia esula, and knapweeds, especially Centaurea stoebe ssp. micranthos. Persistent grazing will further diminish native perennial cover, expose bare ground, and increase exotics (Johnson and Swanson 2005). Darambazar et al. (2007) cite Johnston (1962) that when bare ground is approximately 15%, reduced infiltration and increased runoff occurs in Festuca grassland ecosystems. Fire further stresses livestock-altered vegetation by increasing exposure of bare ground and consequent increases in exotic annuals and decrease in perennial bunchgrass. Grazing effects are usually concentrated in less steep slopes although grazing does create contour trail networks that can lead to addition slope failures. Fire suppression leads to deciduous shrubs (Symphoricarpos spp., Physocarpus malvaceus, Holodiscus discolor, and Ribes spp.) and in some areas trees (Pseudotsuga menziesii) to increase (WNHP 2011).

Festuca campestris is highly palatable throughout the grazing season, and summer overgrazing for 2 to 3 years can result in the loss of Festuca campestris in the stand. Although a light stocking rate for 32 years did not affect range condition, a modest increase in stocking rate led to a marked decline in range condition. The major change was a measurable reduction in basal area of Festuca campestris. Long-term heavy grazing on moister sites can result in a shift to a Poa pratensis - Phleum pratense type. Pseudoroegneria spicata shows an inconsistent reaction to grazing, increasing on some grazed sites while decreasing on others. It seems to recover more quickly from overgrazing than Festuca campestris. It tolerates dormant-period grazing well but is sensitive to defoliation during the growing season. Light spring use or fall grazing can help retain plant vigor. It is particularly sensitive to defoliation in late spring. Exotic species threatening this ecological system through invasion and potential complete replacement of native species include Bromus arvensis, Potentilla recta, Euphorbia esula, and all manner of knapweed, especially Centaurea stoebe ssp. micranthos.

Conversion of this type has commonly come from invasive by non-native species such as Bromus tectorum, Centaurea stoebe ssp. micranthos, Centaurea solstitialis, Hypericum perforatum, Poa pratensis, and Prunus cerasifera. These invasive species increase post disturbance including long-term excessive grazing by livestock, or direct soil disturbance from severe trampling by livestock and roads. Altered fire regimes, primarily fire suppression, has allowed succession and conversion to deciduous shrublands (Symphoricarpos spp., Physocarpus malvaceus, Holodiscus discolor, Rosa spp., and Ribes spp.) and in some areas trees (Pinus ponderosa or Pseudotsuga menziesii) to increase (Wikeem and Wikeem 2004, LANDFIRE 2007a, WNHP 2011).

Common stressors and threats include fragmentation from roads, altered fire regime from fire suppression and indirectly from livestock grazing and fragmentation, and introduction of invasive non-native species (WNHP 2011). Potential climate change effects could include a shift to species more common on hotter, drier southern aspects, if climate change has the predicted effect of less effective moisture with increasing mean temperature (TNC 2013).

This lower montane, foothill and valley grassland system occurs throughout the southern interior and southern portion of the Fraser Plateau, as well as the valleys around the Fraser River in the Pavilion Ranges, the Nicola River and the Similkameen River in British Columbia. It also occurs in the mountains and large valleys of northwestern Wyoming and western Montana, east to the central Montana Rocky Mountain Front and mountain "island" ranges, west through Idaho into the Blue Mountains of Oregon.