VULNERABILITY OF RIPARIAN VEGETATION TO CATASTROPHIC FLOODING - IMPLICATIONS FOR RIPARIAN RESTORATION

In this study, we examined the site-specific effects of a large episod ic flood on the riparian vegetation within the floodplain of the San L uis Rey River in southern California. Using multispectral airborne vid eography, we quantified percent cover of riparian vegetation, cultivat ed agricultural land, urban surfaces, upland vegetation, bare soil, an d water within 22 sections of floodplain, both before and after a larg e flood (January 13, 1993). We also quantified the amount of these cov er types within bands of the watershed 1 km wide x 5 km long directly upstream of each floodplain site. The amount of riparian vegetation de stroyed by the flood within each section varied from nearly zero to al most 40% of pre-flood coverage. The magnitude of loss in riparian vege tation was most strongly related to the amount of riparian vegetation initially present in the floodplain and the amount of urban surfaces i n the nearby watershed. These results suggest that riparian vegetation within the San Luis Rey River floodplain is generally at high risk of destruction from large floods, and that this risk is exaggerated in a reas with high urban development. We infer from these results that sit es near existing large areas of intact riparian vegetation and away fr om urban development will have the highest potential for successful lo ng-term restoration.