Abstract
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. Adding the effective crown to biomass equations can enhance the accuracy of the derived biomass. 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. Terrestrial laser scanning (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. The results showed that the minimum crown contact height was very similar to the effective crown height, and an increase in model accuracy was apparent (with R a 2 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. The novelty of the article is that it improves the fit of individual-tree biomass models by adding crown-related variables and investigates how the accuracy of biomass estimation can be enhanced by using remote sensing methods without obtaining diameter at breast height.
Highlights
Forest ecosystems are dominated by trees and other woody plants
Detailed descriptions of crown information based on laser pulses emitted and received by Terrestrial laser scanning (TLS) and the strong correlations between crown parameters and biomass could explain why crown parameters extracted from point cloud data were strongly correlated with biomass
Because TLS has the advantage of describing the spatial structure of trees in detail, crown parameters of three different heights were extracted, and a multiple stepwise regression was performed to determine the position of the effective crown
Summary
Forest ecosystems are dominated by trees and other woody plants. As an important natural resource on Earth, forests bring economic, ecological, and social benefits and are of great significance to human livelihoods, economic development, and social progress. Used crown size parameters include crown length, crown width, crown volume, and crown surface area. The crown profile is a predictor of crown size and can reflect crown length, crown ratio, crown width, crown surface area, crown volume, leaf surface area, and biomass distribution [2,3,4]. Adding crown surface area to the allometric growth equation for estimating the biomass of tropical trees can greatly enhance prediction accuracy, trees with a diameter at breast height (DBH) greater than 95 cm [6]. When crown surface area was added to the biomass equation with tree height as the only dependent variable, the coefficient of determination (R2) of the equation increased from 0.898 to 0.966 [8]
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