Linking process-based and empirical forest models in eucalyptus plantations in Brazil.

The 3-PG model (Landsberg and Waring, 1997) was parameterized to predict potential productivity across 170 000 ha of Eucalyptus grandis hybrid plantation distributed in 19 regions in eastern Brazil. The regions were defined on the basis of meteorological measurements made by automatic weather stations. Mean annual increments estimated by the model for a 6-year rotation were compared with available observations made annually in permanent sample plots (PSPs). The goodness of fit between estimated and observed growth was determined by R2=0.92. Comparisons between model estimates and measurements such as basal area and total volume are presented. An empirical model called E-GROW ARCEL was developed and fitted using PSP data from the same region. The model is based on recovering the parameters of the Weibull probability density function by matching their moments to estimated stand level variables. Stand models were fitted for projections of stand basal area, mortality, dominant height, tree height, DBH (diameter at breast height) variance and stem taper. Volume of log types in the DBH distribution can be estimated. Mean annual increment (MAI), one of the outputs of 3-PG, was used to establish a hybrid approach, linking the two models by matching the relationship between MAI and site index from E-GROW ARCEL. Growth curves and yields are generated. The hybrid approach is being established as a basis for decision making and management of fast-growing E. grandis hybrid plantations in eastern Brazil.