Evaluating the effect of black and white Colobus monkeys on the performance of forest plantations in Western Uganda

Abstract

Tree defects are injuries and growth patterns that reduce the tree’s structural strength, wood quality and lead to growth failure. While studies suggest that a combination of multiple defects lead to growth failure, Individual defects may or not lead to growth failure. The extent to which defects affect forest plantation performance in Uganda is not known. In this study, the various defects on pine trees were assessed and the number of trees with and without defects was compared. The relationship between both monkey defects and non-monkey defects with wood volume was determined. In addition, the effect of defects on tree log quality was examined. The study was conducted in three compartments of pine plantations in Mafuga Central Forest Reserve in Western Uganda. Each compartment was divided into coupes, making a total of 5 coupes. The trees in each coupe were measured for diameter at breast height and were examined for any defects. Measured trees were marked to avoid errors like double counting or skipping. This study revealed several categories of defects including; debarking, broken tops forking of trees or multiple branching, tree sweeps, rotten trees and dead trees. Generalized linear models showed that number of trees with defects was significantly lower than those without defects (χ2 = 20.762, df = 1, p < 0.001). The most common monkey defect on pine trees was debarking while the least common was dead trees. Among the non-monkey defects, non-useable was the most common and fire damage was rare. There was a significant variation in wood volume with monkey defect (df = 5, p < 0.001). The study also demonstrated that monkey defects influence the quality of logs. The results of this study suggest that the pine plantations in Mafuga central forest reserve are well managed but also highlight an urgent need to address the various causes of defects with a view of reducing timber volume and quality lost due to defects.