Forest health along a wet sulfate/ph deposition gradient in north-central pennsylvania

Abstract

A well-defined gradient of wet atmospheric depositions characterized by SO4, NO3, H, and NH4 ions has been described in north-central Pennsylvania. The forests of this region are of the oak/hickory type as they extend across the Allegheny Plateau. Sulfate levels along a 160-km west-east gradient varied from approximately 40 kg/ha to 25 kg/ha in the western and eastern portions, respectively. The objective of this research project was to determine if forest trees along the gradient showed anomalous characteristics that might be related to acidic atmospheric deposition. Trees were relatively healthy across the gradient, as measured by observations of crown transparency, twig dieback, and trunk condition. No general relationship was apparent between overall tree health and deposition patterns. Specific disorders noted at greater frequencies at the high deposition portion of the gradient included the presence of insect borers on white oak trunks and early fall coloration of red maple. Disorders observed at greater frequencies at the low deposition portion of the gradient included twig and branch dieback of red oak, white oak, and red maple; chlorosis of red oak; and thrips injury of red maple. A direct cause-and-effect relationship between the pollution gradient and these disorders has not been established.