BENEFITS OF PROTECTIVE FENCING TO PLANT AND RODENT COMMUNITIES OF THEWESTERN MOJAVE DESERT, CALIFORNIA

Human disturbance in the western Mojave Desert takes many forms. The m ost pervasive are livestock grazing and off-highway vehicle use. Over the past few decades several areas within this region have been fenced to preclude human disturbance. These areas provide opportunities to s tudy the impact of human activities in a desert ecosystem. This paper documents the response of plant and small mammal populations to fencin g constructed between 1978 and 1979 at the Desert Tortoise Research Na tural Area, Kern County, California. Aboveground live annual plant bio mass was generally greater inside than outside the fenced plots during April 1990, 1991, and 1992. The alien grass Schismus barbatus was a n otable exception, producing more biomass in the unprotected area. Forb biomass was greater than that of alien annual grasses inside the fenc e during all three years of the study. Outside the fence, forb biomass was significantly higher than that of alien grasses only during sprin g 1992. Percent cover of perennial shrubs was higher inside the fence than outside, while no significant trend was detected in density. Ther e was also more seed biomass inside the fence; this may have contribut ed to the greater diversity and density of Merriam's kangaroo rats (Di podomys merriami), long-tailed pocket mice (Chaetodipus formosus), and southern grasshopper mice (Onychomys torridus) in the protected area. These results show that protection from human disturbance has many be nefits, including greater overall community biomass and diversity. The significance and generality of these results can be further tested by studying other exclosures of varying age and configurations in differ ent desert regions of the southwestern United States.