Uneven-aged Management of Longleaf Pine Forests Using Selection Silviculture

Abstract

Approximately 38 million hectares were dominated by longleaf pine (Pinus palustris Mill.) forests in the Southeastern United States prior to European settlement. Frequent disturbances, especially fire, made this species dominant, and also created an uneven-aged, irregular forest structure in the region. However, with the arrival of Europeans, exploitation of longleaf forests began, large areas were cleared, and as a result, about 97% of longleaf forests were lost to agriculture or conversion to other dominant species such as loblolly pine (Pinus taeda L.). Although a concern about the restoration of longleaf ecosystems has increased in recent years, practical methods to accomplish this goal are only beginning to be implemented. Beginning in the 1950s, many of the original restoration studies on regeneration of longleaf pine focused on even-aged (EA) silvicultural techniques because these techniques were considered logical and appropriate for use with shade and competition intolerant species such as longleaf pine. Those methods were successful for regenerating stands, but, the unique longleaf ecosystem has not been fully restored by these approaches. Natural uneven-aged (UEA) longleaf pine ecosystems exhibit a rich biodiversity; however, ecological values such as biodiversity, recreation, aesthetics and wildlife are not fully restored by the regular structure created with EA techniques. At the same time, the UEA mosaic of small EA groups that were present in natural longleaf forests suggests that UEA methods should be successful if we can determine the timing and intensity of disturbance. I believe that residual basal area (RBA) may be an important factor in longleaf pine seedling establishment and sapling recruitment into the canopy. Thus, in this study, the effects of varying levels of RBA (9.2, 13.7, and 18.4 m2 ha-1) on longleaf pine germination, survival, establishment and growth under selection silviculture using single-tree selection based on the Proportional-Basal Area (Pro-B) method were observed. There was a statistically significant relationship between the number of germinants and RBA during the germination period and the following three growing seasons. Mortality of germinants was not affected by RBA during the first two growing seasons following germination. In addition, RBA did not affect either mortality or growth of planted seedlings during the first and second growing seasons. However, RBA influenced the impact of a growing season fire on the survival of germinants and planted seedlings at year two. In the third growing season, RBA negatively affected the size of both germinants and planted seedlings. Survival rate and number of seedlings at the end of third growing season suggest that UEA methods may be successful for regeneration and restoration of longleaf pine forests, and an alternative to EA methods in longleaf pine forests. Moreover, the comparison of RBA and stocking suggests that stocking may be a better indicator when allocating growing space in longleaf pine forests. Additional measurements are needed to determine the efficacy of UEA methods in these forests. Current data aims to broaden our understanding of how overstory density affects seedling germination, growth, and mortality within longleaf pine forests of southeastern USA.