A comparison of harvester productivity and stump volume waste in coppiced and planted eucalyptus grandis pulpwood compartments in the KwaZulu-Natal forestry region of South Africa

Over the past decade the South African forestry industry has gradually experienced the ramifications of labour scarcity, increases in labour costs, the effect of HIV and AIDS and increasing timber demand. Consequently, this has led to an increase in the mechanisation rate, especially in timber harvesting operations. Due to the labour challenges in South Africa, mechanised forestry equipment has increasingly been required to operate in complex forest conditions, such as coppiced compartments, where they have not operated before. It therefore occurs that harvesters are either used in certain coppiced compartments with uncertain productivity expectations, or the harvesters are not used in these compartments due to a lack of productivity knowledge. The influence that certain factors have on harvester productivity and stump volume loss – factors such as coppice regeneration practices and stem form – is poorly understood and has not been quantified. No scientific research exists regarding the effects of coppice compartments on the productivity of a harvester and the amount of stump volume waste. This research aimed at determining the influence of tree volume, tree form, stem felled first and distance between stems on the productivity of an excavator based harvester in coppiced double, coppiced single and planted Eucalyptus grandis pulpwood compartments. Furthermore, the research determined whether there was any stump volume waste, and quantified how much of it was due to excessive stump heights by the harvester. Through regression analysis, productivity equations were derived to make productivity predictions in both coppiced and planted compartments. All stumps were evaluated for waste and the average stump volume waste in coppiced double, coppiced single and planted trees was determined. The research results showed that planted trees had the highest productivity across all tree sizes, followed by coppiced single trees and then coppiced double stems. When harvesting a 0.2 m3 tree, the mean harvester productivity was 8.7 m3 per PMH in coppiced double trees, 13.8 m3 per PMH in coppiced single trees and 16.1 m3 per PMH in planted trees. In coppiced double stems the productivity was not significantly influence by the distance between stems. However, the productivity was significantly influenced by the stem felled first. The regression results showed that if the smaller stem was felled first, the productivity would increase if the larger stem’s volume was less than 0.18 m3; however where the larger stem was greater than 0.18 m3, the relationship was reversed. In addition, the productivity for both coppiced single trees and coppiced double stems were significantly influenced by stem form. The poorly formed trees had low productivity compared to the trees with good form. The stump volume findings showed that coppiced double stems had the highest average stump volume waste per stump, with 0.00307 m3 waste, followed by coppiced single trees (0.001954 m3) and planted trees (0.001650 m3). The average stump volume waste per stump with…