Models to predict whole-disk specific gravity and moisture content in planted longleaf pine from cutover and old field sites

Abstract

Efforts to restore longleaf pine across the southeast United States have occurred on two distinct site types: cutover forests and old agricultural fields. We measured wood and bark physical properties of unthinned planted longleaf pine from 16 stands across Georgia, ages 12 to 25, with eight stands sampled from each site type. Three-hundred and twenty trees were felled and 3572 disks collected from within the trees. Wood and bark specific gravity (SG), moisture content (MC), and proportion of bark were measured. Non-linear mixed effects models were developed to predict the variation in wood and bark SG with respect to relative height, age, and site type. Cutover sites had higher whole-tree wood SG (0.504 vs 0.455) and bark SG (0.374 vs 0.347) than old agricultural fields. The models explained 50% and 37% of the variability in wood and bark SG, respectively. Moisture content models were fitted as a function of SG for wood (R2 = 0.87) and bark (R2 = 0.71). Bark thickness, dry mass, and green volume were higher for cutover forest sites. Trees sampled included both defect-free and defect-containing trees; however, no significant differences in the wood physical properties were found. These results provide important information for the utilization of plantation longleaf pine.