ABSTRACT

Damage to the understory of shelterwood systems during generational succession is an issue that has been debated for a long time. In this study, we analyzed the spatial relationship between damaged understory trees and harvested trees during the final cutting in a shelterwood forest stand dominated by Chamaecyparis obtusa (cypress) in central Japan. We surveyed the positions of all cypress trees and observed the final cutting operation. By measuring the felling direction, the physical contact between the harvested trees and understory trees was reproduced using the Geographic Information System (GIS). Logistic regression was performed using the extracted frequencies of physical contact as explanatory variables and variables important for reproducing the spatial pattern of the damaged understory were selected. The model selection indicated that the damage to the understory could be explained by the contact between the understory trees and the crowns and trunks of felled trees. The understory height was relatively ineffective in explaining the spatial damage pattern. The model could reproduce the spatial distribution of damage rates more realistically than conventional models which depend on the distance from stumps or roads. It was quantitatively revealed that controlling the felling direction was an important factor in mitigating understory damage.

摘要

在世代传承过程中对防护林系统林下林木的破坏是一个争论了很长时间的问题。在这项研究中，我们分析了在以Chamaecyparis obtusa为主的防护林林分最终砍伐期间受损林下树木和采伐树木之间的空间关系（柏树）在日本中部。我们调查了所有柏树的位置，并观察了最后的切割操作。通过测量砍伐方向，使用地理信息系统 (GIS) 再现了采伐树木和林下树木之间的物理接触。使用提取的物理接触频率作为解释变量进行逻辑回归，并选择对再现受损林下空间格局重要的变量。模型选择表明，对林下林木的破坏可以通过林下林木与被砍伐树木的树冠和树干之间的接触来解释。林下高度在解释空间破坏模式方面相对无效。与依赖树桩或道路距离的传统模型相比，该模型可以更真实地再现损坏率的空间分布。定量表明，控制采伐方向是减轻林下损害的重要因素。