Abstract
Overabundant deer and other large herbivores can degrade ecosystems and hamper restoration efforts. We examined the recovery of forest understory vegetation and tree regeneration following intensive deer management at Duke Farms, a 1108-ha preserve in central New Jersey, USA, severely degraded by extremely high densities of deer (> 80 km(-2)) and non-indigenous plant species. A 2004 deer cull followed by sustained hunting pressure reduced deer densities to 3.8 km(-2) inside a 260-ha deer exclosure, and similar to 14 km(-2) outside. We monitored understory conditions between 2008 and 2019 in both areas using rapid presence/absence assessment techniques and compared stem density measures with regional and historical datasets to assess tree regeneration. Native vegetation rebounded rapidly, increasing in vertical density at browse height by 4.9% per year inside the exclosure and 2.0% outside, while non-native vegetation increased 3.0% and 2.4% per year, respectively. Larger (> 30 cm) native tree seedlings became 12x and 5x more abundant inside and outside the exclosure, respectively, relative to nearby forests lacking aggressive deer management. Native shrubs and palatable herbs that were virtually eliminated before deer culling began, however, remain scarce. Our results demonstrate that reducing deer densities can enhance our ability to restore forested habitats, even in extremely degraded sites where the region as a whole remains severely impaired. Simple methods may be used to track these improvements, but both management and monitoring must be sustained, and forest understories may need to be augmented by actively planting native species and/or controlling non-native species to ultimately succeed.