Washington Native Plant Society: Natural Processes in the Shrub-Steppe

Natural Processes of the Shrub-Steppe

The primary historical ecological processes at work in the shrub-steppe ecosystem are drought and fire. Shrub-steppe plant species have developed particular adaptations to low annual precipitation and summer drought conditions. Species' varying abilities to persist in different soil moisture regimes, for example, influences their distribution on the landscape. Similarly, the frequent fire regime in the shrub-steppe creates a patchywork of shrub-dominated areas and grass-dominated areas. Hot, dry conditions and flammable vegetation have historically resulted in late summer and early fall fires that are estimated to have occurred every 30-70 years. Bunchgrasses and other species with below-ground storage organs are adapted to fire; their root systems are not killed by fire allowing them to resprout quickly. Some species, such as sagebrush, are killed by fire. Sagebrush does not resprout and must recolonize by seed dispersed from adjacent unburned areas. Recolonization by sagebrush is slow; estimates are between 50-100 years, depending on characteristics of a burned area. This difference in fire resilience creates large areas of steppe, bunchgrass and wildflowers where fire has removed sagebrush; and large areas of shrub-steppe, or unburned areas. Together these processes create the complex habitat mosaic known as the shrub-steppe ecosystem.