%0 Research article
%T Calibrating predicted tree diameter distributions in Catalonia, Spain
%A Palahí, Marc
%A Pukkala, Timo
%A Trasobares, Antoni
%D 2006
%J Silva Fennica
%V 40
%N 3
%R doi:10.14214/sf.332
%U https://silvafennica.fi/article/332
%X Several probability density functions have been used in describing the  diameter distributions of forest stands. In a case where both the stand  basal area and number of stems per hectare are assessed, the fitted or  predicted distribution is scaled using only one of these variables, with  the result that the distribution often gives incorrect values for the  other variable. Using a distribution that provides incorrect values for  known characteristics means wasting information. Calibrating the  distribution so that it is compatible with the additional information on  stand characteristics is a way to avoid such wasting. This study  examined the effect of calibration on the accuracy of the predicted  diameter distributions of the main tree species of Catalonia. The  distributions were calibrated with and without considering the  prediction errors of the frequencies of diameter classes. When  prediction errors were assumed, the calibration was done with and  without making allowance for estimation errors in the stand level  calibration variables. Calibrated distributions were more accurate than  non-calibrated in terms of sums of different powers of diameters. The  set of calibration variables that gave the most accurate results  included six stand variables: number of trees per hectare, stand basal  area, basal-area-weighted mean diameter, non-weighted mean diameter,  median diameter, and basal area median diameter. Of the tested  three-variable combinations the best was: number of trees per hectare,  stand basal area, and basal-area-weighted mean diameter. Means were more  useful calibration variables than medians.