Productivity and cost of whole-tree harvesting without debarking in a Eucalyptus nitens plantation in Tasmania, Australia

Abstract

There is increasing interest worldwide in using tree harvesting biomass as an energy source. Bark retained on logs is commonly used as an energy source, but is generally removed from eucalypt logs during harvest. In order to evaluate the potential use of eucalypt bark as fuel, there is a need for information on the productivity and cost implications of retaining eucalypt bark during harvest operations. The study examined the impact of retaining bark on logs on the productivity and costs of a whole-tree to roadside harvesting system in a short-rotation Eucalyptus nitens plantation in Australia being harvested for pulp logs. Trees were felled and bunched with a feller-buncher in spring, then left infield for four weeks to promote bark adhesion and reduce bark loss. A skidder extracted the trees to roadside where a processor processed them to predominantly 10 m logs. Machine productivities were calculated from estimated tree and log volumes and cycle times recorded from video recordings. The feller-buncher’s productivity (65 m³ PMH₀⁻¹) was less than expected as it appeared to be underpowered to handle the larger trees on the study site. The skidder’s productivity (56 m³ PMH₀⁻¹) was comparable to those reported in studies under similar conditions and with bark retained. The roadside processor’s productivity (25 m³ PMH₀⁻¹) was lower than expected.This was believed to result from the operator separately stacking 10 m and 5 m logs, and the lower feed speed resulting from slippage due to the reduced feed roller pressure used in the study to reduce bark loss. Future research could identify feed rollers that increase feed speed while retaining bark. Harvest system costs (AUD18 GMt⁻¹) were similar to those reported for a eucalypt roadside processing trial where bark was removed. These results suggest that retaining bark on the logs at roadside did not affect the harvesting system’s productivity or costs.

Keywords: Whole tree to roadside, harvest system, bark, bioenergy, biomass, Eucalyptus nitens, Australia