Many landscapes in West Virginia have lost native tree species due to a history of human disturbances. Of particular concern are native species that were removed and are not returning through natural regeneration. We predicted that the lack of recruitment of native tree species was due to two barriers to recruitment that occur in degraded forests around the world (1) herbaceous competition, and (2) herbivory. In order to identify barriers to tree recruitment, we established plots in forest and field environments with two site treatments, planted seedlings of four economically important native tree species, and monitored natural tree regeneration. Tree species chosen for re-introduction were: Castanea dentata (American chestnut), Quercus rubra (red oak), Acer saccharum (sugar maple), and Picea rubens (red spruce). Seedlings were monitored for survival and growth in the presence or absence of 1) herbicide application to reduce competing ground vegetation and 2) fences to exclude Odocoileus virginianus (white-tailed deer).
Results/Conclusions
After three growing seasons (2005 - 2007), red spruce had the greatest overall survival (64%) and mean height growth (9.5 cm). Red spruce performance was resistant to both deer and herbaceous competition, and performance was consistent in field and forest condition. Thus, red spruce was distinguished as not limited by site factors, but apparently limited by seed dispersal and/or germination. In contrast, the other three species tested had very low to zero survival when exposed to deer. American chestnut had low survival and growth across all treatments, suggesting basic climate and/or soil limitations. Vigorous natural regeneration of Prunus serotina (black cherry) occurred in forest plots with both herbicide and deer exclusion (1.2 stems/m2). Thus, black cherry was distinguished as having the most vigorous natural regenerating when multiple site factors (deer, herbaceous vegetation) were excluded. Our study identified a full range of responses from the species tested, from no site factor barriers to predominantly one barrier, to two interacting barriers, to fundamental barriers, demonstrating the individualistic response of species and the importance of testing multiple recruitment barriers and species at once.
