Improved allometric equations for estimating biomass of the three Castanopsis carlesii H. forest types in subtropical China

Abstract

Estimation of forest biomass is of great significance for determining the most effective way to analyze carbon storage and dynamics. To enhance the accuracy of such estimations, the development of locally not pantropically—derived reliable allometric models is advised whenever possible, especially for dominant and widely distributed tree species, such as in the Castanopsis carlesii H. (C. carlesii) forests in subtropical China. Here, C. carlesii allometric equations were developed and applied to examine for three subtropical forests: a natural primary forest, an artificial-assisted naturally regenerated secondary forest and a C. carlesii plantation. To develop these allometric equations, destructive measurements of architecture and biomass of above- and below-ground components were undertaken for 33 sample trees from 10 dominant species, with stem diameters (at 1.30 m, or above buttresses) ranging from 4 to 67 cm. The mixed-species regressions with only the diameter at breast height as a predictor gave the best-fitting allometric relationship for biomass estimation of foliage, branch and coarse roots; the inclusion of tree height gave the best-fitting allometric relationship for estimation of stem and total biomass. Adding wood density did not improve model performance. Dominant-species regression for C. carlesii was able to predict biomass well using only diameter at breast height as a metric, but adding height and wood density slightly improved the goodness-of-fit, indicating that wood density and tree height may be crucial factors in above- and below-ground biomass models of these subtropical forests. The mixed-species regressions were able to predict well the total biomass of both primary and secondary forests, while the dominant-species models gave a better fit for estimating biomass of the C. carlesii plantation. The biomass estimates of the secondary forest was significantly higher than those of the C. carlesii plantation, indicating that intense forest regeneration practices might cause the reduction of above- and below-ground forest biomass. Therefore, distinct models for the biomass estimation of mixed forests and pure plantation are likely to be needed to improve the accuracy of both biomass assessment protocols and estimations of C sequestration for subtropical forests.