Douglas-fir’s productivity for growth zones in the Argentinean Patagonian Andes

Abstract

The objective of this study was to evaluate different growth zones of Douglas-fir [Pseudotzuga menziesii (Mirb.) Franco] in the Argentinean Patagonian Andes and to characterize them based on their potential productivity. Three preliminary zones were defined based on their precipitation regimes, since this is the most important climatic factor in the region. These zones lied within the isohyets that goes from 600 to 1,000 mm of annual precipitation, other from 1,000 to 1,400 mm, and the third one from 1,400 mm and up. For each zone and for the whole region, site and top height functions were adjusted by using stochastic differential equations. The database was obtained from stem analysis of 126 trees. These trees were selected from 71 temporal plots established on 64 stands. Height growth and site index functions were fit for the whole region and for each growth zone. The height growth was modelled by a stochastic differential equation in wich the deterministic part is the Richards model. All parameters are estimated by a maximum likelihood procedure. The polymorphyc model with the free origin was the best. The evaluation of the models defined for each zone and their comparison with the use of a regional model was made through graphic and statistical analyses (likelihood ratio test). The results showed that the regional model was not satisfactory to predict productivity of Douglas fir for the whole Patagonian region. Therefore, the growth zones and the functions of site and dominant height growth which have been presented are recommended as the better predictors of the potential productivity of Douglas-fir plantations growing in Patagonia.