Volume modeling and yield for Liriodendron tulipifera based on terrestrial laser scan data

  Objective  Liriodendron tulipifera is an excellent timber species. It is of great significance to study the volume model of L. tulipifera wood and analyze the yield of merchantable timber under different densities for the efficient cultivation of L. tulipifera plantation.

  Method  In this study, the terrestrial laser scan (TLS) data was obtained in the multi-density L. tulipifera plantation area in Jiangsu Province of eastern China. The single tree parameters (DBH, tree height H, volume V) were extracted for the various densities (2 m × 2 m, 3 m × 3 m, 4 m × 4 m, 5 m × 5 m) of the L. tulipifera sample stand. The single entry volume model was conducted and the taper equation model was established. The timber yield of each density stand was calculated by the taper equation.

  Result  The quadratic formula with one variable: V=0.000\;3 D^2 + 0.006\;5 D-0.036\;9 was obtained as the single entry volume model for L. tulipifera wood in the study area. The model’s coefficient of determination (R²) was 0.884. After the test of residual standard deviation (S_EE), systematic error (T_RE), mean relative error (M_SE), precision estimation (ρ) and other indicators, there was no obvious systematic deviation, so the model can be used to estimate the volume of L. tulipifera in the study area. This study selected the improved Schumacher’s equations as taper equation for different afforestation densities, the model’s R² was 0.924, root mean square error (RMSE) was 1.454, and M_SE was 0.050, ρ was 0.910, etc. Furtherly, the taper equation was used to make multi-diameter grade wood in the multi-density afforestation forest sample plots. It was found that the output rate of large-diameter timber was the highest (39.582%) under 4 m × 4 m density planting forest, the output rate of small-diameter timber was the highest (81.250%) under 2 m × 2 m density planting forest, and the maximum composite yield was 4 m × 4 m density planting forest (98.650%).

  Conclusion  For L. tulipifera plantation under the multi-density management, the yield of large-diameter timber in the open forest is the largest, while the small-diameter wood is the main diameter class in the dense forest. The single tree parameters obtained based on the ground laser point cloud could be intuitively studied for the forest manager, which has a positive impact on the improvement of the production and management level of the plantation and the improvement of the work efficiency of the forestry workers.