Columbia Basin Canyon Grassland

These grasslands are similar floristically to Columbia Basin Palouse Prairie (CES304.792) but are distinguished by landform, soil, and process characteristics. They occur in the canyons and valleys of the Columbia Basin, particularly along the Snake River canyon, the lower foothill slopes of the Blue Mountains, and along the main stem of the Columbia River in eastern Washington. Occurrences are found on steep open slopes, from 90 to 1525 m (300-5000 feet) elevation. Annual precipitation is low, ranging from 10 to 25 cm (4-10 inches). Settings are primarily long, steep slopes of 100 m to well over 400 m, with soils derived from residuum and having patchy, thin, wind-blown surface deposits. Slope failures are a common process. Fire frequency is presumed to be less than 20 years. The vegetation is dominated by patchy graminoid cover, cacti, and some forbs. Pseudoroegneria spicata, Festuca idahoensis, and Opuntia polyacantha are common species. Deciduous shrubs Symphoricarpos spp., Physocarpus malvaceus, Holodiscus discolor, and Ribes spp. are infrequent native species that may increase with fire exclusion.

The vegetation is dominated by patchy graminoid cover, cacti, and some forbs. Pseudoroegneria spicata, Festuca idahoensis, and Opuntia polyacantha are common species. Deciduous shrubs Symphoricarpos spp., Physocarpus malvaceus, Holodiscus discolor, and Ribes spp. are infrequent native species that may increase with fire exclusion.

These dry grasslands are distinguished by landform, soil, and process characteristics. Annual precipitation is low, ranging from 12-25 cm (5-10 inches) that occurs mostly in the winter, primarily as rain. They occur in the canyons and valleys of the Columbia Basin, particularly along the Snake River canyon, the lower foothill slopes of the Blue Mountains, and along the main stem of the Columbia River in eastern Washington. Occurrences are found on steep open slopes, from 90 to 1525 m (300-5000 feet) elevation. Landform settings of this grassland are primarily long, steep slopes of 100 m to well over 400 m in length, with colluvial soils derived from residuum and having patchy, thin, wind-blown surface deposits. Bare ground, gravel and rock between bunches are common features due to frequent soil movement and sun exposure. Biological soil crust cover is usually present but generally decreases with increasing vascular plant cover, elevation, loose surface rock, and coarseness of soil. Elk, deer and bighorn sheep are native large grazers in the canyon who used these grasslands, particularly in winter and spring (Tisdale 1986).

This grassland primarily occurs on long, steep slopes. Surface disturbances from slope failure are a common process. Most slips result from saturated soil layers over frozen ground (Tisdale 1986). Fire is the primary disturbance factor. Historically, fire resulted in top-kill and some mortality, although the overall grassland was not changed. Fires were low intensity due to limited fuel and significant internal spacing between fuel patches. Currently, cheatgrass and other introduced grasses often invade these habitats after fire. The historic frequency was 5-20 years. Fire frequency is presumed to be less than 20 years; the return interval may have been as low as 5-10 years (Landfire 2007a).

Biological soil crust cover diminishing or eliminated 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).

In the early 1900s, heavy sheep and cattle grazing led to an increase of shrubs into much of the area, although shrubs generally don't occur in the canyon grassland (Landfire 2007a). Currently, the primary land uses that alter the natural processes of this system are associated with livestock practices, annual non-native species invasion, fire regime alteration, direct soil surface disturbance, and fragmentation (WNHP 2011). Excessive grazing stresses the system through soil disturbance, diminishing or eliminating the biological soil crust, altering the composition of perennial species, and increases the establishment of native disturbance-increasers and annual grasses particularly Bromus tectorum and exotics forbs such as Centaurea solstitialis. Persistent grazing will further diminish perennial cover, expose bare ground, and increase exotic annuals. Darambazar et al. (2007) cite Johnston (1962) that when bare ground is approximately 15% reduced infiltration and increased runoff occur in fescue 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. Due to steepness of terrain, grazing effects are usually concentrated in less steep slopes, although grazing does create contour trail networks that can lead to addition slope failures.

In more mesic canyon steppe, fire suppression leads to deciduous shrubs (Symphoricarpos spp., Physocarpus malvaceus, Holodiscus discolor, and Ribes spp.) and in some areas trees (Pinus ponderosa or Pseudotsuga menziesii) to increase (WNHP 2011). Additional disturbances, such as vehicle tracks, will increase the probability of alteration of vegetation structure and composition and response to fire as discussed above. Invasive perennial exotics such as Hypericum perforatum, Poa pratensis, and Prunus cerasifera are major site stressors. Davies et al. (2009) conclude that sites with heavy litter accumulation (e.g., ungrazed Artemisia tridentata ssp. wyomingensis / Festuca idahoensis - Achnatherum thurberianum community) are more susceptible to exotic annual invasion following fire than those with less litter accumulation. They note that introduced species and changes in climate can change ecosystem response to natural disturbance regimes.

Tisdale (1986) notes that canyon grasslands are "highly stable, with boundaries that are unlikely to change without a sizeable shift in climate." And that "grassland community changes caused by heavy grazing do not appear to have altered their pattern of distribution."

Conversion of this type has commonly come from agriculture (wheat farming) in less steep foothill sites, historically (Landfire 2007a). Currently, conversion is to invasive non-native species such as Bromus tectorum, Centaurea solstitialis, Hypericum perforatum, Poa pratensis, and Prunus cerasifera. These invasive species increase post disturbance including excessive grazing by livestock, or direct soil disturbance from severe trampling by livestock and roads. Altered fire regimes, including frequent fires, result in annual, non-native brome-dominated sites. On mesic sites, fire suppression has allowed succession and conversion to deciduous shrublands (Symphoricarpos spp., Physocarpus malvaceus, Holodiscus discolor, and Ribes spp.) and in some areas trees (Pinus ponderosa or Pseudotsuga menziesii) to increase (Landfire 2007a, WNHP 2011). Common stressors and threats include fragmentation from agriculture and roads, altered fire regime from fire suppression and indirectly from livestock grazing and fragmentation, 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).

Occurs in the canyons and valleys of the Columbia Basin, particularly along the Snake River canyon, the lower foothill slopes of the Blue Mountains, and along the main stem of the Columbia River in eastern Washington, on steep open slopes, from 90 to 1525 m (300-5000 feet) elevation.