The Sagebrush Cooperative

NW High Desert: Sagebrush Systems

Viable sagebrush ecosystems consist of a diverse plant and animal community. With increasingly degraded and fragmented landscapes, interrupted disturbance regimes, and pressure from invasive species, the persistence of these ecosystems and their diverse plant and animal associations is uncertain.

Sagebrush is usually the dominant shrub in the Intermountain West where precipitation is greater than 178 mm and soils are salt free (Cronquist et al. 1972). Sagebrush ecosystems are among the most diverse in number and endemism of native plant and animal species in the Intermountain West. Sagebrush habitats are characterized by limited water resources and periodic droughts. Precipitation is spatially and temporally variable and the distributions of species and ecosystems are greatly influenced by temperature and precipitation regimes. A high proportion of annual precipitation falls as winter snow, and spring snowmelt and runoff provide necessary water resources to maintain stream and river channels that support reproduction and survival of riparian and aquatic species. Elevation of sagebrush communities ranges from 150-3300 m (Rickard and Vaughn 1988, Cronquist et al. 1994)

Sagebrush habitats are generally characterized by the sagebrush overstory which is both spatially and temporally diverse due to the large area occupied by the sagebrush ecosystem (Miller and Eddleman 2001, Schroeder et al. 1999). The dominant sagebrush taxa and level of sagebrush dominance or cover on a site is determined primarily by soils and climate, topography, and disturbance history (West 1983). Sagebrush taxa that dominate the Intermountain West are the big sagebrush (Artemisia tridentata) group represented by the subspecies basin big sagebrush (Artemisia tridentata ssp. tridentata), Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), and mountain big sagebrush (Artemisia tridentata ssp. vaseyana), along with two low sagebrush species; low sagebrush (A. arbuscula), and black sagebrush (A. nova). The big sagebrush subspecies are usually found on well drained moderately deep sandy to clay loam soils. Wyoming big sagebrush is usually found on the warmer, drier sites on elevations ranging between 150 to 1,200 m while mountain big sagebrush is found on relatively cooler sites varying from 1,200 to 3,200 m. The low forms of sagebrush are generally found on shallow or poorly drained soils (Eckert 1957, Fosberg and Hironaka 1964).

Within the range of the Sagebrush Cooperative, 3 geographic subdivisions can be defined within the Northwest High Desert (Miller and Eddlemen 2001). The northern reaches of the Cooperative area are contained within the Columbia Basin subdivision. This area is underlain by vast lava flows, soils are generally sandy or silty loams, precipitation occurs primarily in the winter and spring and the dominant sagebrush species are Wyoming big sagebrush and basin big sagebrush (Rickard and Vaughn 1988). Most of south-central Oregon lies within the Northern Great Basin subdivision. Soils here are predominantly derived from volcanic materials, precipitation occurs primarily in the winter and spring and the dominant sagebrush species are Wyoming big sagebrush, mountain big sagebrush and low sagebrush (Walker and McLeod 1991, West 1983). Eastern Oregon, Northern Nevada and Idaho lie within the Snake River Plain subdivision. Habitat in this area lies upon a variety of soils derived from lava flows, alluvial fans and sedimentary materials (Hironaka 1979, West 1983). Precipitation events in the summer increase from west to east. Wyoming big sagebrush and basin big sagebrush dominate the lower elevations while mountain big sagebrush is found at higher elevations.

Along with the sagebrush overstory that generally defines a sagebrush community, the understory associated with these systems is also important and diverse. The understory can contain several vegetation layers which may include 1) forbs and caespitose grasses (bunch grasses), 2) low growing grasses and forbs, and 3) cryptogametic soil crusts. The understory layers are utilized as food and shelter and are essential to the survival of many of the wildlife species that inhabit sagebrush communities (Miller and Eddleman 2001). Although the high desert regions of the Intermountain West are dominated by sagebrush habitats, a mosaic of other habitats such as riparian meadows, steppe dominated by native grasses and forbs, willow (Salix spp.), and sagebrush habitats with some conifer or quaking aspen (Populus tremuloides) are almost always intermixed in a sagebrush-dominated landscape (Griner 1939, Patterson 1952, Dalke et al. 1963, Savage 1969).

Long-term dynamics of sagebrush ecosystems extend over centuries or millenniums. Shifts in plant associations within sagebrush systems over time have primarily been caused by long term changes in climate and catastrophic disturbances, such as volcanic eruptions, resulting in changes in disturbance regimes and distribution of sagebrush, graminoids (grasses and grass-like plants), pinyon, juniper, and salt desert within sagebrush ecosystems (Antevs 1938, 1948, Davis 1982, Mehringer 1985). The most recent change in climatic patterns impacting sage steppe started in the late 1800s. A warmer, wetter climatic pattern has resulted in conifer expansion into previously sagebrush-dominated habitat that has exceeded anything that has previously occurred during a similar length of time (Miller and Wigand 1994, Miller and Tausch 2001).

Concurrent with climatic shifts in the late 1800s, human settlement of the west brought excessive grazing, fire suppression, invasive species and agricultural conversion to the sagebrush steppe. The result was loss and fragmentation of sagebrush habitat, invasive species dominance, top-soil loss and decline in sagebrush steppe dependent wildlife species. A recent assessment of habitat threats in Great Basin ecosystems identified 207 species of conservation concern associated with sagebrush habitats, including 133 plants, 11 reptiles and amphibians, and 63 birds and mammals (Rowland et al. 2005). Much of the Northwest High Desert has been less affected by human influence and comprises one of the largest remaining blocks of high quality sagebrush steppe in the West. Restoration efforts, education, adaptive management and proper land stewardship can assist with keeping this portion of sagebrush steppe habitat a healthy refuge for wildlife that depend on this ecosystem for survival.