Modeling thinning effects on ring width distribution in loblolly pine (Pinus taeda)

Abstract

Measurements were made on loblolly pine (Pinus taeda L.) from permanent sample plots to study the effects of thinning on ring width distribution and to develop a ring width prediction model. Thinning significantly increased ring width over most of the tree bole, and its effects tended to persist over the 12 years since thinning. Significant regional variation in average ring width was evident, with average ring width tending to decrease from the Highlands, to the Coastal Plain, to the Piedmont. A ring width prediction model that accounts for position in tree, tree size, stand, and site factors as well as thinning effects was developed. While ring width showed considerable variation within trees and among trees, the model predicted a substantial portion of the variation in ring width. The model can be used to obtain reasonably good volume estimates in individual growth rings, thus enabling the direct evaluation of the effects of silvicultural treatments on volume production. The data used in this study consisted of correlated observations; hence, direct covariance modeling was used to address biases in the standard error of estimates and hypothesis tests.