Washington Native Plant Society: The Shrub-Steppe Ecosystem

About the Shrub-Steppe

The Columbia Basin is a cold desert. In this semi-arid environment where shrub-steppe is the dominant ecosystem, annual rainfall and seasonal temperatures control the distribution of plant and animal communities. Drought characterizing regions east of the Cascades is due to the "rainshadow effect". A rainshow is caused when a coastal mountain range captures most maritime moisture moving inland with prevailing westerly winds, so that little precipitation reaches inland areas. The rainshadow effect contributes to large differences in annual precipitation between east and west sides of the Cascades. West of the Cascades, annual rainfall ranges from 33 to 42 inches per year, whereas the eastside receives as little as 3 to 6 inches per year at the lowest elevations, and at higher elevations up to 16-18 inches per year. In addition, summer and winter inland temperatures are not attenuated by the ocean as on the west side of the Cascades, so that summer highs regularly top 100 degrees, and winter lows are below freezing.

Plants and animals adapt in surprising and interesting ways to the harsh, semi-arid conditions. Cacti store water in fleshy stems. Many plants have summer and winter dormancy adaptations, such as large, deep below-ground storage organs. A waxy coating on the leaves of some species such bitterroot limits water loss through leaf tissue. Sagebrush has developed tiny, silvery hairs that deflect the drying wind.