The use of tree level vs. stand level data in forest planning calculations — does it really matter?

This study examined how the type of compartment inventory data affects the outcome of forest planning calculations. The inventory data alternatives were tree level data vs. a set of stand characteristics. When stand characteristics were used the diameterdistribution of trees was predicted from the stand variables. For this, prediction models for the parameters of the diameterdistribution of stand basal areawere developed for seven main tree species in Catalonia. An optimisation approach was used to find the coefficients of the parameters models. The predicted diameterdistribution was either scaled to yield the measured total stand basal area, or calibrated with the help of more than one stand characteristics. Individual tree data were used as a reference method to which the stand level data and the alternative ways to derive the diameterdistributions were compared. The methods were compared in terms of calculated inventory results, growth predictions and treatment prescriptions (harvest removals per compartment) for the province of Lleida in Catalonia. The results showed that tree- and stand-level inventory data give very similar results. Calibration of the predicted diameterdistribution improved the accuracy of forest planning calculations. When stand basal area, number of trees per hectare and basal-area- weighted median diameterwere used to calibrate the diameterdistributions the results were rather close to those based on tree level inventory data.