Two steps forward, two steps back: Hunting pressure reductions reverse gains made by browse-sensitive plants

Browsing by overabundant white tailed deer ( Odocoileus virginianus ) alters plant community composition through time, increasing fern and grass abundance while decreasing forb abundance and recruitment of some tree species. We investigated whether intentional reduction of deer density reduced or even reversed negative effects on plant communities, resulting in increased abundance and diversity of browse-sensitive or preferred forage plants in forest understories. We measured understory species richness and abundance, tree regeneration, and growth proxies of three phyto-indicator species for 20 years, a period when deer management changed in intensity. During increased hunting pressure in Kinzua Quality Deer Cooperative, deer densities decreased from approximately 10 deer/km 2 to 5 deer/km 2 for 14 years before increasing to approximately 8 deer/km 2 when hunting pressure was relaxed. During reduced deer pressure, understory plant diversity increased, abundance of browse-sensitive growth forms and tree species increased, and growth proxies for phyto-indicators. However, subsequent increases in deer density and browsing pressure reversed gains in species richness, abundance of browse-sensitive growth forms, and growth proxies for two phyto-indicators while causing plateaus in the regeneration of tree seedlings and saplings. Interestingly, time lags in recovery and reversal differed widely, depending on the species and direction of the change. These results suggest that reducing deer browsing intensity on a landscape will allow browse-sensitive growth forms and species to begin increasing in abundance and increase overall community diversity, but these increases may be quickly reversed if deer densities rise again. Variable time lags complicate management decisions and require a clear formulation of goals and target species. • Sustained reduction in deer browsing pressure for 10 + years can result in increases in understory species richness and community diversity. • Herbaceous phyto-indicators and woody plants both respond to sustained decreases in deer density. • Subsequent increases in deer density and browse pressure reduce species richness and community diversity.