Modelling the effect of thinnings on the diameter distribution of even-aged Maritime pine stands

The purpose of this study was to compare the performance of three different methods of modelling the effect of thinnings on the future diameter distribution of even-aged Maritime pine stands ( Pinus pinaster Ait.). The study material was sampled from a regional spacing study in Galicia (Spain) consisting of 80 diameter distributions before and after thinning. In the first two methods, the management-based modifications are predicted in terms of the change of the diameter distributions described using the three-parameter Weibull probability-density function. These cases require the applications of least squares analyses to predict future Weibull parameters as a function of the thinning type. The third method, which does not require regression analysis, is based on a distribution-independent approach whereby the survival rate of a tree is predicted directly from the relative cumulative diameter distribution before thinning and the thinning weight. For the criteria evaluated in the present paper, the second and third methods have shown superior qualities. However, the second method has an additional advantage that can define a validity range of thinning types as a function of a specified prediction error.