The continued management of mature longleaf pine ecosystems in the southeastern United States carries many challenges when so few examples of old-growth longleaf pine remain, and these are compounded by the unprecedented climatic shifts expected in this region in the coming century. Understanding the sensitivity of mature longleaf pine to various potential stressors, including precipitation extremes, increasingly hot growing seasons, and the impact of tree-to-tree competition within neighborhoods, is increasingly important. We compiled a dendrochronological record of mature longleaf pines (n>130), dating back to the early 20th century, from a study site in southwestern Georgia. In order to explore the differentiating effects of climate, competition, and soil on annual growth (and particularly on responses to drought), we built a statistical model of annual growth as a function of an individual’s size, the degree of competition within its neighborhood (i.e. a radius of 20 meters from the targeted individual), the temperature and precipitation experienced within a given year, and the moisture capacity of the soil in which it grows.
Results/Conclusions
Our longleaf pine ring chronologies displayed sensitivity to annual summer precipitation and climatic aberrations such as drought and flooding events. Interestingly, our model detected no effect of intra-neighborhood competition on the annual growth of our sampled trees; similarly, basal area density in our sampled neighborhoods had no significant effect on average annual growth over the last decade. We posit that this is a consequence of the relatively low average basal area density maintained in our stands by frequent prescribed fire. We did detect a site effect wherein trees in more xeric sampling areas displayed higher sensitivity to summer precipitation than trees in more mesic areas. Climate and soil characteristics appear to have a greater impact on annual growth than intra-stand competition. Results have implications for future management of longleaf pine savanna ecosystems, where hardwood thinning and removal is frequently a priority.