ABSTRACT Soil disturbances are unavoidable in ground-based skidding operations and it is well-known that the extent and severity of disturbances increase with increasing traffic frequency of harvesting equipment and soil conditions (e.g. soil moisture at the time of harvesting). It is unclear, however, how different traffic intensities and soil moisture contents affect the extent, size and intensity of damage inflicted upon residual trees and how these factors might further interact with the layout of skid trails. Skid trail layout in this study is concerned with the horizontal course of the trail that encompasses straight sections and curves of different deflection angles (i.e. narrower and wider curves). Due to expected rolling of logs and vehicle off-tracking in curves, we hypothesised that damage to residual trees would be greater in curves than on straight sections of skid trails and that damage would be greatest in the narrowest curves. We further hypothesised that the relationship between tree damage and curvature would hold regardless of traffic intensity and soil condition. To test these hypotheses, we conducted a survey of the residual stand damage caused by ground-based skidding operations for different trail curvatures and traffic intensities at two Hyrcanian forest sites in northern Iran with different soil conditions. The studied treatment combinations included three curvatures of the skid trail (i.e. narrow curve with a deflection angle of 60°–75°, wide curve with a deflection angle of 110°–130°, no curve (straight trail)), and three traffic frequencies (low, medium and high traffic intensity) of a rubber-tyred cable skidder operated on a clay soil with 18% soil moisture content (Site 1) and a clay-loam with 33% soil moisture content (Site 2). The percentage of damaged trees varied between 45% (Site 1) and 68% (Site 2). The results showed that the number of damaged trees as well as the distance from the skid trail edge to which trees were damaged increased significantly at both sites with increasing traffic frequency, increasing curvature (i.e. narrowing curve) and their interaction. Further, location, size and intensity of damage to residual trees varied significantly with curvature, traffic intensity and soil condition. At each traffic frequency, narrow curves exhibited more damaged trees and damaged trees were found at greater distances to the edge of the skid trail than in wide curves. The average damage area was 86 cm2 and 125 cm2 in Sites 1 and 2, respectively. The significant effect of trail curvature on the location, size and intensity of damage of residual trees has major implications for the design of a skid trail system capable of preserving residual tree quality.

中文翻译：

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滑道曲率对残余树木损伤的影响

摘要 在地面集材作业中，土壤扰动是不可避免的，众所周知，扰动的程度和严重性随着收割设备的交通频率和土壤条件（例如收割时的土壤湿度）的增加而增加。然而，目前尚不清楚不同的交通强度和土壤水分含量如何影响对残留树木造成的损害程度、大小和强度，以及这些因素如何进一步与滑道布局相互作用。本研究中的滑道布局涉及包括直线段和不同偏转角的曲线（即更窄和更宽的曲线）的水平路线。由于原木的预期滚动和车辆在弯道中偏离轨道，我们假设弯道对残留树木的破坏会比滑道的直线段更大，并且在最窄的弯道中受到的破坏最大。我们进一步假设，无论交通强度和土壤条件如何，树木损坏和曲率之间的关系都将成立。为了验证这些假设，我们在伊朗北部具有不同土壤条件的两个希尔卡尼亚森林地点对不同路径曲率和交通强度的地面滑移作业造成的残余林分损害进行了调查。研究的处理组合包括三种曲率的滑道（即偏转角为 60°–75° 的窄曲线、偏转角为 110°–130° 的宽曲线、无弯道（直线路径））和三种交通频率（低，中等和高交通强度）的橡胶轮胎电缆集材机在土壤含水量为 18% 的粘土（场地 1）和土壤含水量为 33% 的粘壤土（场地 2）上运行。受损树木的百分比在 45%（站点 1）和 68%（站点 2）之间变化。结果表明，随着交通频率的增加、曲率（即变窄的曲线）及其相互作用的增加，两个站点的受损树木数量以及树木受损的滑道边缘的距离显着增加。此外，残树受损的位置、大小和强度随曲率、交通强度和土壤条件而显着变化。在每个交通频率下，窄曲线显示出更多受损的树木，并且与宽曲线相比，在距滑道边缘更远的距离处发现受损树木。站点 1 和站点 2 的平均损坏面积分别为 86 cm2 和 125 cm2。路径曲率对残留树木的位置、大小和损坏强度的显着影响对于能够保持残留树木质量的滑道系统的设计具有重要意义。