Resumo

GOMEZ-GARCIA, Esteban; CRECENTE-CAMPO, Felipe  e  DIEGUEZ-ARANDA, Ulises. Above-ground biomass equations for birch (Betula pubescens Ehrh.) and pedunculate oak (Quercus robur L.) in north western Spain. Madera bosques [online]. 2013, vol.19, n.1, pp.71-91. ISSN 2448-7597.

The aim of this study was to develop models for above-ground biomass estimation for birch (Betula pubescens Ehrh.) and pedunculate oak (Quercus robur L.) in Galicia (northwest of Spain). Data from a destructive sampling of 50 birch trees and 50 pedunculate oak trees, that provided total dry biomass weight and dry biomass weight by components: wood, bark, branches over 2 cm, branches between 0,5 cm and 2 cm, branches under 2 cm, and leaves, was used. Different models were fitted for each above-ground component and the best of them was chosen in a first step. All the models were refitted simultaneously by use of Nonlinear Seemingly Unrelated Regressions (NSUR) to ensure the additivity of the biomass equations. Weighted regression was necessary to correct the heterocedasticity of residuals. Not serious problems with multicollineality were observed. Finally, a system of seven equations for the different above-ground biomass components, and for the total biomass, was obtained for each species. These equations explained at least 79% of the observed variability. For total biomass the equations explained 98% and 97% of the observed variability for birch and oak, respectively. The developed biomass equations are recommended in substitution of the existing regional biomass equations.

Palavras-chave : Addivity; simultaneous fitting; Galicia; heterocedasticity; multicollineality.