[en] One of several procedures for estimating carbon stocks in forests is the estimation of tree or stand biomass based on forest inventory data. The two approaches normally used to convert field measurements of trees to stand biomass values are allometric biomass equations and biomass expansion factors (BEFs). BEFs are used in published National Forest Inventory results in which biomass is not estimated or as a complement of growth models that do not include biomass predictions. In this paper, the effectiveness of BEFs for estimating total stand biomass in Portuguese Eucalyptus globulus plantations was analyzed. Here, BEF is defined as the ratio of total stand biomass (aboveground biomass plus root biomass) to stand volume with bark. To calculate total biomass, an equation was developed to estimate root biomass as a function of aboveground biomass. Changes of BEF with stand variables were analyzed. Strong relationships were observed between BEF and stand age, stand basal area, stand volume and dominant height. Consequently, an equation to predict BEF as a function of stand variables was fitted, and dominant height was selected as the predictor stand variable. Estimates of total stand biomass based on individual tree allometric equations were compared with estimates obtained with a constant BEF (0.77), used in the Portuguese National Inventory Report on Greenhouse Gases, and with estimates obtained using the dominant height-dependent BEF equation developed in this work. The BEF prediction model proposed in this work may be used to improve E. globulus Portuguese biomass estimates when tree allometric equations cannot be used.

[es] El objetivo es estimar las reservas de carbono en los bosques mediante la comparaci&oacute;n de dos m&eacute;todos: ecuaciones alom&eacute;tricas de biomasa y los factores de expansi&oacute;n de la biomasa (BEF). Las estimaciones de la biomasa total del rodal, basado en las ecuaciones alom&eacute;tricas de &aacute;rboles individuales se compararon con las estimaciones obtenidas con unos factores de expansi&oacute;n constante de la biomasa (BEF) de 0.77, utilizados en el Informe del Inventario Nacional de Portugal de gases de efecto invernadero, y con las estimaciones obtenidas utilizando la ecuaci&oacute;n de altura dominante de BEF desarrollada en este trabajo. En este trabajo se analiz&oacute; la eficacia de la BEF para estimar la biomasa total del stand en portugu&eacute;s plantaciones de Eucalyptus globulus. Aqu&iacute;, el BEF se define como el cociente de la biomasa total del stand (biomasa a&eacute;rea m&aacute;s la biomasa de ra&iacute;ces), situ&aacute;ndose el volumen con corteza. Para el c&aacute;lculo de la biomasa total, se desarroll&oacute; una ecuaci&oacute;n para estimar la biomasa de ra&iacute;ces en funci&oacute;n de la biomasa sobre el suelo. Se analizaron los cambios de BEF con las variables del rodal. Se observ&oacute; una gran relaci&oacute;n entre el BEF y la edad del rodal, el &aacute;rea basal, el volumen y la altura dominante. Por lo tanto, se ajust&oacute; una ecuaci&oacute;n para predecir el BEF en funci&oacute;n de las variables del rodal, seleccionando la altura dominante como la variable independiente predictora. El modelo de predicci&oacute;n de BEF propuesto en este trabajo puede ser utilizado para mejorar las estimaciones de biomasa de E. globulus portugueses cuando las ecuaciones alom&eacute;tricas de &aacute;rboles no se pueden utilizar.