Impact of a flood on southern California riparian vegetation

This study assesses flood impacts on riparian vegetation in two watersheds within the Transverse Ranges. Data collected in 1993 were compared to basel ine data from 1990 to measure the effect of a 1992 flood. T-tests were used to test for significant post-flood changes in overall vegetation character istics, and vegetation change was regressed on drainage area to test for sp atial variation in flood impacts. Results of means comparisons for the over all data set suggest that the impacts of the flood were insignificant. Howe ver, these results in part are artifacts of data agglomeration, as regressi on results suggest that changes in total cover and diversity are spatially varied, with profound impacts at some downstream sites. The relative cover of mast species remained constant, reflecting an environment in which frequ ent floods help to maintain a vegetation assemblage that is not entirely fl ood resistant, but at least uniform across species in its degree of resista nce.