Allometric equations of select tree species of the Tibetan Plateau, China

Abstract

The Tibetan forest is one of the most important national forest zones in China. Despite the potentially important role that Tibetan forest will play in the Earth’s future carbon balance and climate regulation, few allometric equations exist for accurately estimating biomass and carbon budgets of this forest. In the present study, allometric equations, both species-specific and generic, were developed relating component biomass (DW) to diameter at breast height (DBH) and tree height (H) for six most common tree species in Tibetan forest. The 6 species were Abies georgei Orr., Picea spinulosa (Griff.) Henry, Pinus densata Mast., Pinus yunnanensis Franch., Cypresses funebris Endl. and Quercus semecarpifilia Smith.. The results showed that, both DBH-only and DBH2H based species-specific equations showed a significant fit (P<0.05) for all tree species and biomass components. The DBH-only equations explained more than 80% variability of the component biomass and total biomass, adding H as a second independent variable increased the goodness of fit, while incorporating H into the term DBH2H decreased the goodness of fit. However, not all DBH-H combined equations showed a significant fit (P<0.05) for all tree species and biomass components. Hence, the suggested species-specific allometric equations for the six most common tree species are of the form ln(DW) = c + αln(DBH). The generalized equations of mixed coniferous component biomass against DBH, DBH2H and DBH-H also showed a significant fit (P<0.05) for all biomass components. However, due to significant species effect, the relative errors of the estimates were very high. Hence, generalized equations should only be used when there are too many different tree species, or there is no species-specific model of the same species or similar growth form in adjacent area.