Loblolly pine (Pinus taeda) trees experiencing dieback have altered resin canals, earlywood, and latewood relative to asymptomatic trees

Loblolly pine ( Pinus taeda L . ) stands along the fall line between the Piedmont and Coastal Plain physiographic regions periodically experience dieback events whereby gradual dying of tree branches, shoots, and/or roots can occur, ultimately resulting in tree mortality. The objective of this study was to compare resin canal features and wood properties of loblolly pine trees from planted stands along the fall line in Georgia, aged 21–30 years, with and without signs of dieback. Seven symptomatic and seven asymptomatic stands were selected for sampling. Increment cores were collected at breast height (1.37 m) from ten each of the following tree-types: 1) “healthy” trees from asymptomatic stands; 2) “healthy” trees from symptomatic stands; and 3) “unhealthy” trees from symptomatic stands. Radial ring-level properties, including basal area growth (basal area increment), resin canal size (cross-sectional area), specific gravity (SG) values for the earlywood, latewood, and the entire ring, and ultrasonic velocity (USV), were determined from a total of 210 cores. Models were developed to predict each property as a function of tree group and cambial age. Compared to asymptomatic healthy trees, symptomatic unhealthy trees had significantly lower basal area growth, higher earlywood SG, lower latewood SG, and smaller resin canals. Ring SG and USV were not different between tree-types, however basal area weighted USV was higher in the asymptomatic healthy trees. No traumatic resin ducts were found. Altogether, this study provides detailed information on the wood properties and resin canal features of loblolly pine trees experiencing dieback relative to those from asymptomatic stands.