Determining the effect of tree size, bark-wood bond strength and tree form on the productivity of an excavator-based harvester in Acacia mearnsii in the KwaZulu-Natal forestry region of South Africa

Abstract

The aim of this study was to determine the effect of tree size, bark-wood bond strength and tree form on the productivity of cut-to-length harvesting of Acacia mearnsii, using an excavator-based harvester with a SP Maskiner harvester head in the KwaZulu-Natal forestry region of South Africa. Tree diameter and height measurements were used to determine individual tree volumes, after which the trees were classified into different bark-wood bond strength and tree-form classes. Time studies were carried out to determine harvester productivity. The results showed that tree size plays a crucial role in the productivity of the harvester, but bark-wood bond strength and tree form also influence productivity. The harvester productivity varied from 5.5 m³ per productive machine hour (PMH) in 0.05 m³ trees to 16.9 m³ PMH⁻¹ in 0.25 m³ trees The bark-wood bond strength did not influence harvester productivity when handling small trees of less than 0.1 m³. In small trees, the productivity of the harvester was also not affected by different form classes, but as tree size increased, there was greater productivity variation between the different form classes.