%0 Research article
%T Modelling percentile based basal area weighted diameter distribution
%A Kangas, Annika
%A Mehtätalo, Lauri
%A Maltamo, Matti
%D 2007
%J Silva Fennica
%V 41
%N 3
%R doi:10.14214/sf.282
%U https://silvafennica.fi/article/282
%X In percentile method, percentiles of the diameter distribution are  predicted with a system of models. The continuous empirical diameter  distribution function is then obtained by interpolating between the  predicted values of percentiles. In Finland, the distribution is  typically modelled as a basal-area weighted distribution, which is  transformed to a traditional density function for applications. In  earlier studies it has been noted that when calculated from the  basal-area weighted diameter distribution, the density function is  decreasing in most stands, especially for Norway spruce. This behaviour  is not supported by the data. In this paper, we investigate the reasons  for the unsatisfactory performance and present possible solutions for  the problem. Besides the predicted percentiles, the problems are due to  implicit assumptions of diameter distribution in the system. The effect  of these assumptions can be somewhat lessened with simple ad-hoc  methods, like increasing new percentiles to the system. This approach  does not, however, utilize all the available information in the  estimation, namely the analytical relationships between basal area, stem  number and diameter. Accounting for these, gives further possibilities  for improving the results. The results show, however, that in order to  achieve further improvements, it would be recommendable to make the  implicit assumptions more realistic. Furthermore, height variation  within stands seems to have an important contribution to the uncertainty  of some forest characteristics, especially in the case of sawnwood  volume.