Improving height prediction of regrowth eucalypts by incorporating the of site trees in a modified Chapman-Richards equation

Abstract

Summary Height and diameter equations were developed using the Chapman-Richards function for 30 species in the regrowth forests of southeast New South Wales. These species included all commercial species of eucalypts and non-commercial small tree species of acacia and allocasuarina in the region. To improve prediction accuracy, the mean height and mean diameter of 50 largest regrowth trees/ha were incorporated in a modified Chapman-Richards function: where H and D represent total tree height in m and diameter at breast height in cm, H50 and D50 are the mean height and mean diameter of 50 largest trees/ha in m and cm respectively, a, b, c and d are parameters. Detailed evaluation of prediction accuracy through resampling showed that the incorporation lead to unbiased and more precise prediction for tree height and stem volume of most species and for stand volume of the regrowth forests. The common practice of calibrating height prediction from species-specific individual tree height-diameter equations against measured stand height can underestimate total stand volume between 3%and 5%.