Effects of pine-hardwood management practices on forest regeneration and woody species diversity at the Savannah River Site, South Carolina, USA

In 1989, mixed hardwood-pine forest sites at the Savannah River Site in South Carolina were chosen by USDA Forest Service employees for use in a study of the effects of a combination of forest management practices on woody species composition and diversity. The sites were surveyed for species composition, harvested commercially, burned using several severities, and planted with pine seedlings during 1990. In 1991 and 1993 the sites were surveyed again by Forest Service employees for post-disturbance species composition. I recovered and compiled the earlier pre- and post-disturbance data, and resurveyed the sites in 2002 to compare the immediate effects and the possible persistence of effects of the management treatments on woody species composition and diversity over an 11 year period. The treatment combinations represented a range of disturbances: two harvesting treatments (dormant and growing season commercial clearcuts), three site preparation bum treatments (high severity bum, low severity bum, or no bum), and two pine regeneration treatments (planting of Pinus taeda L. seedlings and natural regeneration). Twelve sample plots, representing all possible treatment combinations, were established in each of three replications for a total of 36 plots. Woody stems were counted and identified in samples in each of the 36 plots at ages one, three, and 11 years. I compared density and diversity values (Shannon-Wiener diversity, richness, and equitability) among treatment combinations using analysis of variance (ANOV A). The most significant effects on species density and diversity were evident one growing season after the harvest. Season of harvest had the most significant effect on both species densities and diversity, while bum severity had a significant effect on diversity alone. At age three, the same patterns were detected, but were weaker and insignificant. By age 11, Quercus and Carya densities differed significantly between the two harvesting treatments, indicating that this treatment had a lasting effect on these tax.a. Significant differences for the remaining tax.a were no longer evident at age 11. The replicates themselves (physically similar at the time of establishment) were significantly different, in many cases, when considered independently. This indicates that physical site characteristics, likely related to pre-harvest species composition might have had a stronger underlying influence on post-disturbance species composition and diversity than the management treatments. Overall, the results suggest that mixed hardwood-pine forests in the Atlantic Coastal Plain (ACP) consist of species able to vigorously recolonize following disturbances as severe as clearcutting. Although these types of management disturbances might have immediate effects on woody species composition and diversity, the results suggest that these effects are minimal over time in the absence of additional disturbance. If the desired outcome is to minimize changes in diversity and species composition, these strategies can be employed with probable success in mixed hardwood-pine forests of the ACP. However, more research should be conducted that explores management disturbances,that are more intense and frequent (e.g., conversion to pine plantations )-these types of practices are becoming more and more common in ACP ecosystems as the demand for wood and wood products increases