Anthropogenic disturbance regimes and coastal sage scrub recovery: Comparing the long term impacts of grazing and cultivation in Southern California.

摘要

Coastal sage scrub (CSS) is a unique and highly threatened vegetation community in coastal Southern California and northern Mexico, with 90 percent lost to development, agriculture, and invasive species. Understanding CSS recovery is critical to its survival. This study looks at the long-term effects of grazing and cultivation in southern California by tracking the extent of exotic grassland in two valleys in the Santa Monica Mountains over sixty years. The rates of native shrub return in a grazed valley were compared to those in a cultivated valley. Transects compared physical differences of stable and recovering grassland-shrubland boundaries. Native shrubs returned to the grass valley that was grazed nearly one and one-half times faster than the valley that was cultivated. Cultivation may result in a type conversion of CSS to a new steady state of exotic annual grassland. The field transects showed that stable and recovering boundaries had different physical characteristics.