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UBC Theses and Dissertations

A geometric model of skyline thinning damage Ormerod, David William


In thinning, physical damage to the residual trees may result from abrasion during felling and yarding. The amount of damage is primarily a function of the stand geometry, the thinning prescription, and the felling strategy, under a given extraction system. In terms of controlling the level of damage, there are two interdependent aspects to the problem. One is to prescribe a desirable thinning that is compatible with the extraction system. The other is to efficiently engineer the extraction under the given silvicultural constraints. For skyline thinning it is assumed that a geometric model of the stand, and of the extraction system, provides a framework for examining potential physical damage, in terms of this interdependence. Based on a three-dimensional model, skyline thinning is simulated, and indices of potential damage are enumerated. For a sample stand of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), the potential damage is studied as a function of the prescription, and the system parameter that determines the felling directions. Three different selection prescriptions are examined; a Low, a Crown, and a Graded. The synthetic data is discussed in terms of frequency distributions, and as a function of the parameter mentioned. It is demonstrated that the system is very sensitive to this parameter. While the effect of the different prescribed thinnings might be thought to be intuitively obvious, some enigmatic phenomena are apparent. It is proposed that such a study is a means of examining both the silvicultural and engineering aspects of the problem of physical damage in the residual stand, for a skyline thinning system. It is hoped that such deliberation will provide a rational framework to determine the effect of this damage upon thinning regimes.

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