Establishment of allometric models and estimation of biomass recovery of swidden cultivation fallows in mixed deciduous forests of the Bago Mountains, Myanmar

We established allometric models for fallow forests following swidden cultivation, to estimate biomass accurately in the fallows around a village in the Bago Mountains, Myanmar. By harvesting 160 individual trees from 53 species and 132 sample culms from four bamboo species, allometric equations were determined between tree/culm size variables, such as diameter at breast height (D130) and tree/culm height (H), and plant biomass components such as trunk/culm, branch, and leaf biomass in the fallows. The correlation coefficient for the allometric model for total above-ground tree biomass as a function of D1302H was high (0.956), although the value for leaf biomass was relatively low (0.626). In addition, best-fit allometric relationships for four bamboo species were established. All allometric models involving total above-ground biomass for all bamboo species had significantly high R2 values: 0.817 for G. nigrociliata, 0.877 for B. polymorpha, 0.910 for B. tulda, and 0.963 for D. strictus. A comparison between the present models and previously reported equations for above-ground biomass for tropical forests revealed that our allometric models followed the general trend for biomass estimation, with substantial differences among forest types. In addition, our results suggest that when allometric models are developed using destructive sampling methods, either all mixed species combined or select dominant species can be used, although the optimal approach would include models with all species combined to estimate biomass accumulation for mixed-species forests. Using the best-fit allometric models for trees and bamboo, we estimated tree and bamboo biomass at the community level, supplemented by understory and vine biomass. Biomass accumulation in the study area generally increased with fallow age, with a large contribution of bamboo in the fallows. To estimate biomass of secondary forests accurately, especially fallow forests, relevant allometric relationships and the intensity of swidden cultivation must be considered.