General estimation models for above- and below-ground biomass of teak (Tectona grandis) plantations in Thailand

To estimate above- and below-ground biomass in teak ( Tectona grandis ) plantations throughout Thailand, we developed general allometric relationships between tree size parameters (stem diameter and height) and tree biomass (of leaves, stems, and roots). Trees were harvested from 18 plantations within the native range of teak in Thailand and across the area covered by these plantations. Allometric equations for total above- and below-ground biomass showed no significant inter-site differences and high correlation coefficients (0.90–0.99). This similarity across sites may be due to similarities in wood density among different age and/or size of teak trees. The majority of previous biomass estimation models for teak trees gave higher estimated values for both above- and below-ground biomass, suggesting that they should not be applied within Thailand. To estimate belowground biomass using root: shoot ratio (RSR), we evaluated RSR among stands of various ages and sizes. We further identified differences in RSR between Thailand and other regions. Estimated RSR varied among stands and decreased significantly with stand age and average tree size. This relationship suggests that belowground biomass can be estimated from aboveground biomass using RSR. However, RSR values differed among countries and regions. In summary, general allometric equations and RSR value can be used to accurately estimate above- and below-ground biomass in teak plantations across Thailand.