Factors influencing loblolly pine stand health in Fort Benning, Georgia, USA
Loblolly pine (LBP; Pinus taeda L.) stands provide two-thirds of the existing federally protected red-cockaded woodpecker (RCW; Picoides borealis) habitat in Fort Benning, Georgia, USA. However, LBP in this area is suspected to face a forest decline issue, which may risk the sustainability of the RCW population. Land managers are attempting to convert LBP stands to longleaf pine (Pinus palustris Mill.), which once dominated the landscape; however, the transition has to be gradual so current RCW habitat is maintained until longleaf pine stands sufficiently support RCW populations. It is critical to identify environmental factors influencing LBP health and convert LBP stands under poor environment to longleaf pine first. We installed 90 plots (30 x 30m2) in mature (>38 years) loblolly pine forests and measured aspect, slope, soil texture, soil (pH, organic matter, cation exchange capacity, and exchangeable phosphorus, potassium, magnesium, and calcium) and foliar (nitrogen and phosphorus) nutrient, diameter at breast height, light exposure, and crown vigor class (CVC; 1 = good, 2 = fair, and 3 = poor). Stand age, site index, and burning and thinning history were retrieved from existing inventory data. Our results show that site index was the main factor in determining LBP health. Site index showed significant correlation with percentage of LBP in CVC1 (p = 0.04) and CVC3 (p = 0.07). Percentage of LBP in CVC3 tended to decrease as soil texture became finer. Poorer site index and coarser soil likely resulted in water stress during periods of drought leading to higher %CVC3 LBP. Based on these results, conversion to longleaf pine should start from LBP stands on coarser soil (or lower site index) at Fort Benning.