Abstract:We developed allometric relationships between tree size parameters (stem diameter at breast height (dbh), at ground surface (D0) and tree height) and leaf, stem, small-root (diameter <5 mm) and total root biomass in various tropical secondary-forest trees in Sarawak, Malaysia. In total, 136 individuals from 23 species were harvested to measure above-ground parts. Root systems of 77 individuals of 16 species were also excavated. The coefficients of correlation for the obtained allometric relationships between tree diameter and plant-part biomass showed high values, ranging from 0.83 to 0.99. In addition, there were few interspecific differences in relationships for all biomass parts, except for leaves. We also found relatively high coefficients of allometric relationships between tree height and plant-part biomass ranging from 0.83 to 0.94. Comparison of above- and below-ground biomass equations for various tropical rainforests implies that our allometric equations differ largely from the equations for tropical primary forests. Thus, choosing both above- and below-ground allometric equations for biomass estimation in tropical secondary forests of South-East Asia requires careful consideration of their suitability.

Although allometric equations can be used to accurately estimate biomass and/or carbon stock in forest ecosystems, few have been developed for logged-over tropical rainforests in Southeast Asia. We developed allometric relationships between tree size variables (stem diameter at breast height (dbh) and tree height) and leaf, branch, stem and total above-ground biomass in two logged-over tropical rainforests with different soil conditions in Sarawak, Malaysia. The study sites were originally classified as mainly lowland dipterocarp forest and have been selectively logged in the past 20 years. In total, 30 individuals from 27 species were harvested to measure above-ground parts. The correlation coefficients for the allometric relationships obtained for total above-ground biomass as a function of dbh had high values (0.99), although the relationships for leaf biomass had a relatively low coefficient (0.83). We also found relatively high coefficients for allometric relationships between tree height and plant-part biomass, ranging from 0.82 to 0.97. Moreover, there were no differences for allometric equations of total above-ground biomass between study sites. A comparison of equations of above-ground biomass in various previously reported tropical rainforests and pan-tropic general equations imply that our allometric equations differ largely from the equations for tropical primary forests, early successional secondary forest, and even for the general models. Therefore, choosing the biomass estimation models for above-ground biomass in the logged-over forests of Southeast Asia requires careful consideration of their suitability.

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