A comparison between two alternative harvesting systems in the thinning of fast-growing pine plantations under the conditions of low labour cost

A comparative study was conducted in the second commercial thinning of a 12-year-old slash pine (Pinus elliottii Engelm.) plantation in South Africa. The goal of the study was to compare semi-mechanized tree-length harvesting with fully mechanized cut-to-length (CTL harvesting) in terms of: compliance with silvicultural prescriptions, value and volume recovery, productivity, cost and residual stand damage. The two systems were tested on 32 adjacent plots with a mean surface of 4000 m2 each. Plots were randomly allocated to the two treatments, so that each treatment was replicated 16 times. The experiment consisted of a classic time study, followed by the visual inspection of all plots for determining damage frequency and severity. While mechanization allowed a dramatic (tenfold) increase in worker productivity, it also resulted in a proportional increase in team cost, which offset the large efficiency benefit and ended up with both methods incurring similar production cost (180-200 ZAR m3). However, mechanized CTL harvesting resulted in a significant reduction in residual stand damage frequency (from 5.2 to 2.9%) and severity (28% smaller wounds). Mechanized CTL is preferable, because it can reduce the frequency and severity of residual stand damage. In social terms, however, mechanization reduces employment potential but promotes job quality, while conventional harvesting solutions can employ many more people, but offer low-paid, tiresome and potentially hazardous jobs.