%0 Research article
%T Percentile based basal area diameter distribution models for Scots pine, Norway spruce and birch species
%A Kangas, Annika
%A Maltamo, Matti
%D 2000
%J Silva Fennica
%V 34
%N 4
%R doi:10.14214/sf.619
%U https://silvafennica.fi/article/619
%X Information about diameter distribution is used for predicting stand  total volume, timber volume and stand growth for forest management  planning. Often, the diameter distribution is obtained by predicting the  parameters of some probability density function, using means and sums  of tree characters as predictors. However, the results have not always  been satisfactory: the predicted distributions practically always have a  similar shape. Also, multimodal distributions cannot be obtained.  However, diameter distribution can also be predicted using  distribution-free methods. In the percentile method, the diameters at  certain percentiles of the distribution are predicted with models. The  empirical diameter distribution function is then obtained by  interpolating between the predicted diameters. In this paper, models for  diameters at 12 percentiles of stand basal area are presented for Scots  pine, Norway spruce and birch species. Two sets of models are  estimated: a set with and one without number of stems as a predictor.  Including the number of stems as a predictor improved the volume and saw  timber volume estimates for all species, but the improvements were  especially high for number of stems estimates obtained from the  predicted distribution. The use of number of stems as predictor in  models is based on the possibility of including this characteristic to  measured stand variables.