Relationship between Animal Activity and Bare Areas Associated with California Sagebrush in Annual Grassland

Abstract

Thickets of California sagebrush support large populations of small mammals which eliminate grassland vegetation from the vicinity of the shrubs. The effect of the shrubs is density dependent, with greatest effect at more than 50% canopy coverage and virtually no effect at 25% cover and less. The amount of grassland exclusion diminishes rapidly with distance from the shrub stands, but extends beyond the well-defined border zone as rabbit trails. Although scattered shrubs do not exclude grassland vegetation, they apparently protect the grass under their canopies from grazing by cattle. The extent of the bare areas fluctuates greatly over periods of years. The areas denuded by small mammals are populated by diminutive species which do not live in the unbroken grassland, and show a greater species diversity than unbroken grassland.