Growth model for larch in pure and even-aged stands

摘要

A distance independent tree growth model has been determined for pure and even-aged larch stands (Larix sp.) growing in Walloon Region (South Belgium). This model has been built from 2578 larches (Japanese. European and Hybrid larches) in 99 stands.It enables to predict tree circumference increment from circumference, dominant height, basal area, age and site index of stands. Estimating increments of 1283 larches in 48 stands has been used to validate the model that gives unbiased estimates of theincrements (mean error = -0.002 cm with standard deviation of 0,60 cm). The mean absolute error of estimates is 0,46 cm.year~(-1). The model has also been tested to predict the increment of larches in French experimental plots having very different silvicultural treatments. The residues of these estimations depend on the stand basal area: the lesser the stand basal area, the higher the residues of the estimation. A correction factor, linked to basal area through a Bailey and Clutter curve, has been introduced to extend the validity of the model to stands with a basal area lower than 12 m~2 ha~(-1). This factor does not affect the increment estimations if the stand characteristics are close to mean value of the sample used to build the model (correction factor close to 1). The introduction in the model of competition indexes distance dependant or site qualitative variables does not significantly improve the growth model.