Fibre volume losses of eight softwood clearfell harvesting systems in South Africa
A study of both fibre volume loss and related opportunity cost was performed across the South African softwood sawtimber industry to gain information on the actual utilisation of useful fibre and potential loss or gain of opportunity in terms of potential revenue from both field practices and policy. The study quantified volume losses from high stumps, felling and crosscut saw kerf, log allowances, excessive removal of merchantable wood, incorrect log trimming allocation, and utilisable wood left in-field. Eight treatments were examined: four terminated with merchandising at roadside landing and four at merchandising yards. Within the treatments, felling was either motor-manual or mechanised and compartments were classed by average compartment tree size (less than or greater than 1 m 3). Total wood utilisation was found to be 92.07%. Stumps were found to be 7 cm higher than necessary and volume losses because of high stumps were 0.79% and 0.07% for mechanical and motor-manual felling, respectively. For felling saw kerf losses, mechanical felling showed 0.92% loss, whereas motor-manual felling resulted in only 0.15% loss. Incorrect log trimming allowance provided for 0.60% loss. Excessive trimming of logs resulted in 2.02% loss. Volume lost because of crosscutting saw kerf was low at 0.20%, but tops not being extracted resulted in 2.57% loss. Using SIMSAW 6 simulations, these volume losses translated into an additional annual harvested volume of 421 722 m 3 or additional 1 278 ha harvested area, R166 million log value and R393 million net lumber value loss. Total loss was lowest (6.49%) in the average tree size class less than 1 m 3, which was mechanically felled regardless of merchandising location. For the majority of volume loss categories, motor-manual felling caused greater loss when compared to mechanical felling methods. Log trimming allowance consumed 80 604 m 3 annually. The results indicate that the human element may have a greater impact on fibre and value losses than the system choice. Further research is recommended to quantify the effect of the human element. © 2012 Copyright NISC (Pty) Ltd.