Large woody debris protects woody plants from browsing in restoration following Elwha dam removal.

The increasing number of dams approaching the end of their useful lives compels a need for knowledge about how to conduct riparian restoration associated with dam removal. One of the most difficult challenges following dam removal is restoring native vegetation to drained reservoir beds, which can be impeded by ungulate browsing. Woody plant growth can be slow in dry nutrient-poor reservoir sediment, and browsing can impede forest establishment further. We evaluated the potential for large woody debris (LWD) to limit ungulate browsing on riparian trees and shrubs following dam removal in the Elwha ecosystem. We studied LWD mitigation of browsing in the largest former Elwha reservoir and a comparable valley upriver. We measured browse intensity in randomly located plots stratified by LWD extent, from no LWD to complete LWD enclosure. We compared effects of LWD on browse pressure using analysis of variance. LWD reduced browse intensity three-fold in both study areas, but only in plots fully surrounded by LWD. Protection from browse was greatest for plant species preferred by ungulates. These results suggest an effective strategy for restoring forests at dam removal sites and other riparian restoration projects. LWD can protect plants from browsing, but only when it entirely surrounds plants. Planting within LWD clusters or placing LWD clusters in restoration sites can facilitate establishment of forest islands, potentially advancing restoration progress by decades