Modelling the scaling of belowground biomass with aboveground biomass in tropical bamboos

Bamboo forests cover approximately 1% of the total global forest area and thus hold great potential in climate change mitigation. Quantifying the contribution of bamboo forests to ecosystem level carbon storage is challenging because it is composed of a complex system of rhizomes and roots. The belowground biomass (BGB) is an important indicator for ecosystem carbon storage as well as forest assessment and management. Therefore, the objectives of this study are to (1) determine patterns of variation in BGB to AGB ratios with clump formation, stand age and species, (2) quantify allometric scaling between BGB and AGB in the different species, and (3) develop species-specific and generalized biomass estimation models relating BGB with AGB. The highest BGB to AGB ratio (0.92: 1) was recorded in Pseudostachyum polymorphum while the smallest (0.11: 1) was found in Dendrocalamus hamiltonii. The clump-forming species (Schizostachyum dullooa and D. hamiltonii) allocated significantly smaller biomass to belowground parts relative to aboveground parts than Melocanna baccifera and P. polymorphum that form widely spaced culms. In the species that form widely spaced culms, BGB scaled with AGB isometrically (beta = 1), while in the clump-forming species the exponent indicated positive allometry (beta > 1). The best generalized model relating BGB with AGB was ln(BGB) = -9.0 + 0.82(ln((DH)-H-2)). The best species-specific model for total biomass (TB) was the allometric model with diameter at breast height (D) alone.