Monday, August 2, 2010: 2:10 PM
408, David L Lawrence Convention Center
Background/Question/Methods Restoration of the longleaf pine (Pinus palustris) ecosystem is a principle objective of land managers in the southeastern United States, where upland pine sites historically dominated by longleaf pine have been replaced with loblolly pine (Pinus taeda). In natural systems, longleaf pine regeneration is often most successful within canopy gaps, largely due to reduced competitive pressure from canopy trees. Management practices that mimic natural systems may be desirable for restoration of longleaf pine within loblolly pine stands that currently provide ecosystem services. In this study, we investigated the dynamics of planted longleaf pine seedling survival and growth in relation to resource availability within canopy gaps created by harvesting in loblolly pine stands. Our study design is a randomized complete block, with gaps of three different sizes (diameters of 40m, 60m, and 80m) in each of six blocks established within loblolly pine dominated stands across Fort Benning, GA, USA in 2007. Longleaf pine seedlings were planted in rows oriented north/south across each gap in January 2008. Four rows of seedlings were selected and root collar diameter (RCD) of each surviving seedling was measured for two growing seasons. We measured light availability, soil moisture, and water potential of longleaf pine seedling tissue (a measure of moisture stress) at 10-m intervals across each 80m diameter gap.
Results/Conclusions After the first growing season, survival was significantly affected by gap position, with the greatest mortality near the gap center (p < 0.0001). Generally, seedling root collar diameter was not significantly affected by gap position at the end of the first growing season, but RCD was largest near gap center after two growing seasons. Light availability increased with distance from forest edge, and light levels were significantly greater in the northern half compared to southern half of gaps (p = 0.0419). First year mortality was found to be significantly, positively related (p < 0.0001, R2 = 0.2657) to light availability. Gap position did not have a significant effect on either soil moisture or water potential of longleaf pine seedlings in the first growing season, although soil moisture was negatively related to seedling moisture stress (p < 0.0001, R2 = 0.1268). Our results suggest a relationship between site exposure and seedling mortality that may be associated with increased moisture stress; generally, these results contribute to our understanding of gap dynamics in southern pine forests and may have implications for longleaf pine restoration in canopy gaps.
Results/Conclusions After the first growing season, survival was significantly affected by gap position, with the greatest mortality near the gap center (p < 0.0001). Generally, seedling root collar diameter was not significantly affected by gap position at the end of the first growing season, but RCD was largest near gap center after two growing seasons. Light availability increased with distance from forest edge, and light levels were significantly greater in the northern half compared to southern half of gaps (p = 0.0419). First year mortality was found to be significantly, positively related (p < 0.0001, R2 = 0.2657) to light availability. Gap position did not have a significant effect on either soil moisture or water potential of longleaf pine seedlings in the first growing season, although soil moisture was negatively related to seedling moisture stress (p < 0.0001, R2 = 0.1268). Our results suggest a relationship between site exposure and seedling mortality that may be associated with increased moisture stress; generally, these results contribute to our understanding of gap dynamics in southern pine forests and may have implications for longleaf pine restoration in canopy gaps.