Biomass allocation patterns and allometric models of Ginkgo biloba

Based on the Ginkgo biloba plantation in northern area of Jiangsu Province, eastern China, 13 sample trees with different diameters at breast height (DBH) were selected, and used to analyze the relationships between above- and below-ground biomass and their allocation patterns. At the individual tree level, allometric models for each component biomass were developed based on independent variables of DBH, tree height (H), D²H and D^aH^b. The best fitting models were identified by the fitting and test results of parameter estimation, the statistical parameters used in this paper were adjusted determination coefficient (R_adj²), sum of squares for error (SSE), statistics estimating the standard deviation SEE, mean relative deviation (ME), mean relative deviation absolute (MAE), mean estimated error (MPE). The results showed that the whole variation range for plant biomass of the 13 ginkgo trees was 28.50-320.27 kg for each tree. Relative proportions of stem, branch, leaf, and root to total tree biomass were 49.4%-56.6%, 12.1%-18.9%, 3.8%-5.5%, and 26%, respectively. The aboveground biomass was significantly linearly correlated with belowground biomass. The slope of the fitted linear model was 0.35. Results showed that the majority leaf and branch biomass occurred in the middle canopy layers, with significant difference between the middle, upper and lower layers in combined biomass of leaves and branches, and there was no significance between upper and lower layers. For all sample trees, about 70% of roots were observed in the 0-1.0 m soil layer. With soil depth increasing, the root biomass decreased exponentially. At branch level, allometric models based on two variables (i.e. BD and BL) of branch biomass explained more than 95% of the variations in data. The results showed that D was a best independent variable in estimating the biomass of leaf, branch, aboveground section than the rest variables, and D-H was the best in estimating stem, root and total tree biomass. The mean value of proportion of different biomass components showed an order of stem > root > branch > leaf. The middle canopy layers occupied the maximum ratio in vertical and horizontal distribution of branch and leaf biomass, and these results were in consistence with the isometric biomass allocation theory. Allometric models based on independent variables of DBH, and H would be suitable for predicting the above- and below-ground component biomass of ginkgo, and the calculation of ginkgo biomass and carbon storage.