Biodiversity varies considerably in Southern Californian riparian vegetation. The intermediate disturbance hypothesis posits greater diversity in settings that are subject to moderate-intensity disturbance. Flood intensity tends to vary systematically in watersheds, potentially imposing patterns of biodiversity. In two study watersheds, species richness increases with flood severity. Diversity, or heterogeneity, is less predictable: Biodiversity patterns in these watersheds are complicated by atypical patterns of flood severity. Although riparian diversity may be intimately dependent on flood disturbance, the relationship is predictable only with due attention to the physiographic details of individual stream networks.

This paper studies riparian vegetation species diversity in relation to flood disturbance on Piru and Sespe creeks, tributaries to the Santa Clara River, near Ventura, California.