Estimation Of Individual-Tree Biomass Based On Effective Crown Data Using Terrestrial Laser Scanning

Biomass reflects the state of forest management and is critical for assessing forest benefits and carbon storage.The effective crown is the region above the lower limit of the forest crown that includes the maximum vertical distribution density of branches and leaves;this component plays an important role in tree growth.Thus adding the effective crown information to biomass equations can enhance the accuracy of the derived biomass.Because the forest crown has spatial heterogeneity both horizontally and vertically,and the complex structure leads to Directly measure the effective crown is time-consuming and laborious.Crown parameters cannot be accurately measured by traditional field measurements.Terrestrial laser scanning(TLS)can obtain detailed information about the three-dimensional forest structure from the crown layer to the understory,which makes it possible to reconstruct the real spatial structure of individual-tree.Six sample plots in a larch plantation(ranging in area from 0.06 ha to 0.12 ha and in number of trees from 63 to 96)at the Mengjiagang forest farm in Huanan County,Jiamusi City,Heilongjiang Province,China,were analyzed in this study.TLS was used to obtain three-dimensional point cloud data on the trees,from which crown parameters at different heights were extracted.These parameters were used to determine the position of the effective crown.Moreover,effective crown parameters were added to biomass equations with tree height as the sole variable to improve the accuracy of the derived individual-tree biomass estimates when the DBH of the individual-tree of the remote observation ground is difficult to obtain.The results showed that the crown parameters extracted in this paper were strongly correlated with biomass.And the-minimum crown contact height was very similar to the effective crown height,and an increase in model accuracy of the effective crown parameter was apparent(with Ra2 increasing from 0.846 to 0.910 and root-mean-square error(RMSE)decreasing from 0.372 kg to 0.286 kg).The optimal model for deriving biomass included tree height,crown length from minimum contact height,crown height from minimum contact height,and crown surface area from minimum contact height.This article promotes the application of TLS in the extraction of crown parameters,emphasizes the important role of effective crown in forestry resource monitoring,and even provides new ideas for forest biomass derivation using remote sensing for Earth observations.