LINEAR AND NONLINEAR FUNCTIONS OF VOLUME INDEX TO ESTIMATE WOODY BIOMASS IN HIGH-DENSITY YOUNG POPLAR STANDS

Biomass estimations are very important in short rotation high density stands, but usually require some destructive sampling. This paper disc usses the potential use of allometric relationships based on volume in dex (height x diameter squared) for accurate and non-destructive estim ations of stem biomass. When using this approach, one implicitly assum es a constant conversion factor from stem volume index to real stem vo lume as well as a constant wood infradensity (stem dry mass versus fre sh volume), both assumptions being questionable. Our results on five d ifferent poplar clones grown at two different sites (Afsnee, near Gent , Belgium and Orsay, near Paris, France) and under two different cultu ral management regimes underscore the following points: i) stem diamet er measured at 22 cm aboveground and in two perpendicular directions i s a relevant parameter to compute volume index in high density poplar stands; ii) power function regression equations fit the stem volume in dex versus stem dry mass relationship better than simple linear regres sions; iii) attention should be paid to variation in wood infradensity , which ranged from 0.35 to 0.44 kg dm(-3) in our study.