基于TLS的抚育间伐对长白落叶松干形的影响

Effects of thinning on Larix olgensis plantation stem form based on TLS

【目的】探究利用地基激光雷达技术(Terrestrial Laser Scanning,TLS)评价树干形状的可行性,并分析不同间伐方案对人工黄花落叶松(长白落叶松,Larix olgensis)干形的影响。【方法】在黑龙江省佳木斯市孟家岗林场选取5块采用不同间伐处理方案的长白落叶松人工林样地进行地基激光雷达扫描,对预处理后的点云进行单木分割与单木枝干分离,并进一步提取出单木胸径、树高及不同高度处直径等参数,最终计算单木干形的指标并进行理论造材,分析不同间伐方案对人工长白落叶松干形及林分经济价值的影响。【结果】通过与样地实测单木数据对比,基于TLS数据提取得到的单木特征参数精度较高,胸径提取的平均误差仅为-0.39 cm,平均绝对误差百分比达到2.86%,树高提取的平均误差为-0.26 m,平均绝对误差百分比为3.12%;所有间伐措施均能提高林木的胸径和材积,而树高在不同间伐方案之间没有明显差异;林木的干形指标如胸高形数(f_(1.3))、胸高形率(q_(2))及材积分配方式等在不同的间伐方案中表现有所不同,两次高强度间伐的方式使树干材积更多地分配在树干中部;同一林分内不同大小的树木之间干形并无显著性差异;不同的间伐方案对树木根张程度并无影响;不同的间伐方案均可以不同程度的提高林分经济价值。【结论】地基激光雷达对单木参数提取精度较高,能够在无损情况下获取较为准确的单木干形特征;不同间伐方案对树木干形及林分经济价值有不同程度的影响,两次高强度间伐可以最大限度地提升林分的经济价值。

【Objective】The study explored the feasibility of terrestrial laser scanning(TLS)technology to evaluate the stem form,and analyzed the influence of different thinning measures on the stem form of Larix olgensis plantations.【Method】Five sample plots of L.olgensis plantations with different thinning measures in the Mengjiagang Forest Farm,Jiamusi City,Heilongjiang Province,were used to acquire TLS data.The preprocessed point clouds were first segmented into individual trees and classified into stem and non-stem points.Parameters that included diameter breast height,tree height,and diameter at different heights were further extracted.Finally,the indices of individual tree stem forms were calculated,theoretical timber was made,and the effects of different thinning measures on L.olgensis plantation stem form and stand economic value were analyzed.【Result】Compared to field-measured trees,the accuracy of individual tree characteristic parameters extracted based on TLS data was satisfactory.The error results of diameter breast height showed that ME was only-0.39 cm,MAPE was 2.86%,ME extracted from tree height was-0.26 m,and MAPE was 3.12%.All thinning measures improved the diameter breast height and volume growth of individual trees.There was no significant difference in tree height among the different thinning measures.The stem form indices of trees,such as and the volume distribution mode,differed in the different thinning methods,with the stem volume more distributed in the middle of the stem.Stem forms of different sizes did not significantly differ at the same site.The different thinning methods had no effect on the degree of tree root extension.Different thinning measures improved the economic value of stands in different degrees.【Conclusion】TLS exhibits high precision in extracting parameters of individual trees and can be used to obtain the dry shape characteristics of individual trees without destructive sampling.Different thinning measures have different effects on tree stem form and economic value of stands.The two high-intensity thinning measures can maximize the economic value of stands.These results provide a reference for forestry production practices in northeast China.