28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

Plant Community Structure Associated with Livestock Watering Sites in the Central Mojave Desert

J. R. Matchett¹, M. L. Brooks¹, and K. H. Berry^2
1U.S. Geological Survey, Western Ecological Research Center 1160 N. Stephanie, Henderson, Nevada 89074
²22835 Calle San Juan de Los Lagos, Moreno Valley, California 92553

Domestic livestock have grazed the Mojave Desert for over 150 years. Recently, land management agencies have reduced grazing and focused efforts on restoring degraded rangelands. Assessments of plant community changes caused by grazing are lacking in this region, but are required when defining restoration objectives. We quantified plant community structure along a grazing disturbance gradient associated with livestock watering sites in a recently closed grazing allotment. Annual and perennial plants were sampled in interspace and beneath-shrub microhabitats at 0, 50, 200, and 800 m from the edge of 10 watering sites during two years of contrasting rainfall (1998 annuals, 2000 annuals and perennials). Annual plant trends were significant only during 1998 when rainfall was high. Annual plant cover decreased 36% between 0 and 50 m from watering sites, primarily due to declining cover of the aliens Erodium cicutarium and Schismus spp. However, cover of another less abundant alien, Bromus madritensis ssp. rubens, increased with distance from watering sites, indicating that not all alien annuals were more abundant closer to the sites. In contrast, native annual plant cover increased 156% between 0 and 200 m. Within interspaces, total annual plant richness (0.02 m² > scale) increased 68% between 0 and 50 m, and 33% between 50 and 200 m, due to increasing numbers of native species. Beneath-shrub annual richness increased 33% between 0 and 800 m. Perennial cover declined 50%, and perennial richness declined 30, 37, and 48% (at 100, 300, and 600 m2 scales) between 0 and 50 m from watering sites. Structural diversity of perennial plants was unchanged along the gradient, although perennials in the <0.5 m² cover class were less common near watering sites. Our findings suggest that grazing impacts on plant community structure are greatest within 50 to 200 m from watering sites in the central Mojave Desert.