Interactions between livestock grazing, soil characteristics, and vegetation composition in coast range grasslands in central California

Despite a long history of livestock grazing in California grasslands, little is known about the impacts of grazing on soil characteristics and how these soil characteristics and vegetation composition may be linked. Using a ten-year-old, replicated livestock exclosure experiment in coast range garsslands in the Santa Ynez Valley, California, we evaluated the impacts of grazing across three different sites each of which contained 4, 50 x 50 meter exclosures that had not been grazed by livestock for ten years. Areas outside the exclosures were grazed annually with a short duration, moderate intensity winter/spring grazing regime. All sites were dominated by non-native annual grasses although patches of native perennial grasses were scattered throughout most areas. Soil sampling was stratified by ‘native perennial’ versus ‘non-native annual’ grass patches. We found that grazing affected soil characteristics in the annual but not the native perennial grass patches: bulk density of soil in non-native annual grass stands was higher in grazed compared to ungrazed plots while C:N ratios and late spring soil moisture were lower in grazed plots. Nitrogen mineralization potential was not affected by grazing but was higher in non-native annual than native perennial grassland soil samples. Vegetation responses to the exclosures varied strongly between the three sites with few differences between grazed and ungrazed plots in two of the sites and strong differences in the third site. At this site, ungrazed plots had low diversity and were largely dominated by ones species of thatch forming, non-native grass. Overall, native perennial grasses were more common in grazed than ungrazed plots. Potential reasons for variation in grazing effects will be discussed.