Deer browse susceptibility limits chestnut restoration success in northern hardwood forests

Abstract

Efforts to develop American chestnuts [Castanea dentata, (Marsh.) Borkh], with improved resistance to the chestnut blight fungus, Cryphonectria parasitica (Murr.) Barr, and Phytophthora root rot, caused by Phythophthora cinnamomi Rands, are ongoing. Establishing founder populations of improved chestnut will require understanding the ecological and silvicultural requirements of the species. In areas where white tailed deer (Odocoileus virginianus Zimmerman) hinder tree regeneration success, understanding how browsing will affect the establishment of planted chestnut is critical. We evaluated the impact of browsing by deer on survival, growth and competitive status of hybrid chestnuts planted in 15 northern hardwood sites in Pennsylvania. We found that after six years, chestnuts planted in fences were 65 percent taller and 35 larger in basal diameter than chestnuts in unfenced areas. Browsing by deer shifted the competitive dynamics faced by the chestnuts by favoring slower growing, browse tolerant species and reducing the heights of competing woody stems. Nevertheless, the competitive status of chestnuts in unfenced plots remained stagnant over time due to repeated browsing, while it increased in fenced plots over time. Our results suggest that fencing or other means of reducing herbivory will be necessary to protect planted chestnuts in areas with moderate or high deer densities.