PARENT SESSION
Poster Session #6: Conservation Ecology.
Monday, August 6, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

The impact of simulated grazing on native and non-native plants.

Kimball, Sarah¹, Schiffman, Paula¹, ¹

ABSTRACT- Management of California's few remaining valley grasslands aims to increase the cover of native plants relative to aliens. At Carrizo Plain National Monument, cattle grazing is used as a restoration tool to give native plants a competitive advantage. However, European species evolved with livestock while California grasslands were assembled without grazing herds. Thus, cattle may impact natives more negatively than non-natives. We tested this hypothesis by simulating two aspects of grazing, clipping and mulch removal. Plots were unclipped, clipped once, clipped twice, clipped three times, or unclipped with mulch removed. Species richness, percent cover, and reproductive output were recorded. Focal species were also grown in pots and were unclipped, clipped once, or clipped twice. The height, number of leaves, and number of fruits were measured to determine the compensatory responses. Native species richness was significantly impacted by clipping. Clipping significantly decreased native percent cover and even the relative percent cover of native plants. The native grasses Poa secunda and Vulpia microstachys were harmed by clipping. In contrast, the European species Erodium cicutarium and Bromus madritensis were unaffected by clipping in the field. In pots, Bromus madritensis was able to over-compensate following clipping, while native species did not compensate. Mulch removal negatively affected the percent cover and relative percent cover of natives. In conclusion, cattle grazing harms native species in California grasslands.

KEY WORDS: Carrizo Plain National Monument, non-native plants, grazing, grassland