Initial conditions influence effects of prescribed burns and deer exclosure fences on tree regeneration and understory diversity in Appalachian oak-dominated forests

Abstract

Sustaining oak-dominated forests that support regionally important biodiversity in the Appalachian Mountains is a substantial challenge for land managers due to mesophication – a region-wide phenomenon in which forest composition shifts from oaks to shade tolerant, mesic species such as maples. To inform oak forest management that includes biodiversity preservation as a management objective, we established a two treatment factorial design experiment at two sites to determine the effects of prescribed fire and deer herbivory on tree regeneration and understory plant diversity in dry oak-dominated forests. Data were collected before and after treatments were applied. Prescribed burns altered species composition to favor fire-adapted species and deer exclosure fences protected woody and herbaceous species sensitive to deer browse at both sites, however the initial conditions in the forests profoundly influenced the effects of these treatments. Prescribed fires promoted oak seedlings over maple seedling where oak seedlings were well stocked. Conversely, burning favored maple seedlings to the detriment of oak seedlings in areas where chronic over-browsing resulted in a depauperate understory. Although fire reduced understory plant cover at both sites, overall understory species richness was not affected by burning. This suggests that prescribed fire did not have detrimental effects on forest understory diversity, although herbaceous species diversity was significantly reduced by burning the site with an initially depauperate understory. Fencing resulted in large increases in species richness and cover of understory plants, including more than doubling the cover of tree seedlings and the abundance of tall seedlings in fenced plots, as well as shifts in understory composition towards species sensitive to deer browse. The herbaceous layer in this study contained nearly 6 species for every one species found in the tree canopy, reaffirming the importance of the herbaceous layer in the biodiversity of Appalachian oak-dominated forests. These results provide guidance to managers of protected areas seeking to enhance oak regeneration while maintaining or promoting native plant diversity in the forest understory.