New Techniques For Pre-Commercial Thinning -- Time Consumption and Tree Damage Parameters

High costs, increasing density and height of young stands at the time of pre-commercial thinning, and difficulty in attracting personnel to do motor-manual work have called for the development of new techniques for pre-commercial thinning. In the study reported here a new motor-manual and mechanized pre-commercial thinning technique was compared to the conventional brush saw technique in terms of time requirements and damage caused to crop trees. The motor-manual tools tested were a hacksaw and two pole saws with modified chainsaw blades. The mechanized machine prototype was built especially for pre-commercial thinning, and was equipped with a new type of crane tip-mounted device based on a cutting-squeezing technique. Our expectations were that, compared to the brush saw, themechanized approach would be less time-demanding in dense and/or large diameter stands, but more main stems would be damaged. Furthermore, a motor-manual device with a larger cutting area than the conventional brush saw blade should allow faster operation in dense and large diameter stands, without damaging higher numbers of main stems. To test these beliefs, a rig was built that enabled the tools to be compared in experimental stands with different densities and diameters of secondary stems. One of the pole saws and the mechanized prototype machine were competitive with the conventional brush saw in terms of both time requirements and frequency of damage to main stems, especially in dense (i.e. >15000 stems ha-1) and large diameter (>4 cm) stands. The pole saw was competitive despite having a less powerful engine. The mechanized prototype showed more homogenous time consumption, with lower variation than the other tools. Further field studies are needed to compare the tools in economic terms