Absolute and relative changes in tree growth rates and changes to the stand diameter distribution of Pinus taeda as a result of midrotation fertilizer applications

Abstract

Silvicultural treatments have the potential to change the diameter distribution of a stand, which can alter the final product mix of the stand. Growth and yield models need to account for these changes in the diameter distribution to assess the economic viability of the silvicultural operations. We investigated how the diameter distribution of Pinus taeda L. stands changes as a result of midrotation fertilization. Data from 43 installations of a nitrogen and phosphorus midrotation fertilizer trial series established in the southeastern United States were used in the study. The results indicated that both the absolute growth response and the relative growth response of individual trees were greater among the larger trees. A three-parameter Weibull distribution fitted at each study site was used to investigate how the parameters of the distribution changed with time and treatment. The location and scale parameters of the Weibull distribution were both affected by fertilization. Stand variables, such as site index, age, stand density, and mean diameter at time of fertilization, also affected the location and scale parameters. The shape parameter was not affected by any of the treatments in this study.