Analysis of Taper Functions for Larix olgensis Using Mixed Models and TLS

Abstract

Terrestrial laser scanning (TLS) plays a significant role in forest resource investigation, forest parameter inversion and tree 3D model reconstruction. TLS can accurately, quickly and nondestructively obtain 3D structural information of standing trees. TLS data, rather than felled wood data, were used to construct a mixed model of the taper function based on the tree effect, and the TLS data extraction and model prediction effects were evaluated to derive the stem diameter and volume. TLS was applied to a total of 580 trees in the nine larch (Larix olgensis) forest plots, and another 30 were applied to a stem analysis in Mengjiagang. First, the diameter accuracies at different heights of the stem analysis were analyzed from the TLS data. Then, the stem analysis data and TLS data were used to establish the stem taper function and select the optimal basic model to determine a mixed model based on the tree effect. Six basic models were fitted, and the taper equation was comprehensively evaluated by various statistical metrics. Finally, the optimal mixed model of the plot was used to derive stem diameters and trunk volumes. The stem diameter accuracy obtained by TLS was >98%. The taper function fitting results of these data were approximately the same, and the optimal basic model was Kozak (2002)-II. For the tree effect, a6 and a9 were used as the mixed parameters, the mixed model showed the best fit, and the accuracy of the optimal mixed model reached 99.72%.The mixed model accuracy for predicting the tree diameter was between 74.22% and 97.68%, with a volume estimation accuracy of 96.38%. Relative height 70 (RH70) was the optimum height for extraction, and the fitting accuracy of the mixed model was higher than that of the basic model.

A Novel Approach to Characterizing Crown Vertical Profile Shapes Using Terrestrial Laser Scanning (TLS)

“…In this study, the extraction accuracy of CRs at different heights was analyzed explicitly with reference to the branch factor data measured in a field containing 30 planted Korean pine trees harvested via destructive harvesting (Table 2). The extraction accuracy was low in the RDINC range of 0-0.15, stabilized from an RDINC of 0.15, and it remained at approximately 91%, which is consistent with the findings of Li [86]. Although trunk diameter extraction was not performed in this study, it was studied in the vertical direction using point cloud data; so, it can be compared with the results of Li's study for mutual verification.…”

“…Hook., respectively, but they did not provide specific extraction accuracies because they did not have actual field measurement data for reference. Li [86] et al extracted the trunk diameters of Larix olgensis at different heights in the vertical direction based on TLS data, and they found that the accuracy of the trunk diameter extraction decreased sharply when the relative height exceeded 0.9. In this study, the extraction accuracy of CRs at different heights was analyzed explicitly with reference to the branch factor data measured in a field containing 30 planted Korean pine trees harvested via destructive harvesting (Table 2).…”

“…To reduce the influence of the trees' height on the extraction accuracy, the maximum CR extraction accuracy was analyzed in this study in the RDINC range [86]. RDINC ranges were grouped at 0.05 intervals, and then the radius values calculated from the largest branches of each whorl in 30 sampled trees served as reference values to compare and analyze the maximum CR actually measured in each RDINC range and the maximum CR extracted from the point cloud data.…”