Effects of herbivory as an ecological constraint of willow growth at a restored riparian corridor

A critical component of nearly all riparian restoration projects is the rapid successful recovery of native vegetation. The dynamic conditions and diverse biotic community supported by riparian ecosystems can present numerous constraints to restoration efforts. This study investigated stunted growth of arroyo willow (Salix lasiolepis) cuttings planted along the banks of Redwood Creek as part of the National Park Service’s Muir Beach Restoration Project to restore habitat for special status species in California. Based on observations of deer browsing, as well as signs of extensive biomass removal, I designed a field experiment using exclusionary fencing to test the significance of deer browse on growth of recently planted willows. My study design consisted of measuring the difference in growth (height, mean canopy diameter, estimated aerial percent cover, and volume) in relation to three factors (exclusionary deer fencing, side of bank, and willow age) during the 2013 growing season. Results of my study indicate that deer herbivory was a critical stressor contributing to limited growth of recently planted willow cuttings along the restored banks of Redwood Creek. The main effect of exclusionary fencing was very highly significant for all four growth metrics; however, it had the greatest beneficial effect on younger willows in their second growing season along the right bank. Exclusionary fencing can be used as a cost-efficient method for restricting browsing by wild herbivores at riparian restoration sites, most effective when implemented for protecting willows during their first two growing seasons or until they are resilient to the effects of herbivory