Assessment of topsoil disturbance caused by different skidding machine types beyond the margins of the machine operating trail

Abstract

Forest soil disturbances are unavoidable in ground-based skidding operations and it is well-known that the extent, duration, and severity of disturbances increase with increasing trafficking from harvest equipment and slope gradient. It is unclear, however, how different types of harvest equipment affect the extent of disturbance along the margins of skid trails.The aim of this study was to investigate changes in topsoil (0–10 cm depth) physical properties beyond the margins of skid trails in mountainous terrain in response to skidding with three different skidder types with varying tire ground pressure. Three skidder types (rubber tired “Timberjack 450C” skidder (site RT1), rubber tired “TAF E655” skidder (site RT2), “Onezhets 110” crawler skidder (site CS)), two levels of trail gradient (≤20% and >20%), four levels of traffic frequency (4, 8, 15, and 40 passes), and four distances of buffer strip zones (0.5 m intervals from 0 to 2 m in distance) on both sides of the skid trail edges were analyzed. Results showed that topsoil bulk density increased with greater traffic intensity for all skidder types and on both slopes. With increasing traffic intensities topsoil physical properties gradually deteriorated in zones that were further from the skid trail margin. While this process occurred faster on steeper slopes (i.e., fewer passes were required), the pattern was consistent for all three machine types. Consequently, the area adversely affected by skidding machines increased with increasing harvest traffic, with soil conditions within the first 0.5 to 1 m along the skid trail margin more similar to the skid trail itself and the conditions >1 m more similar to untrafficked areas. The significant effect of skid trail slope gradient on increased soil disturbance provides land managers with important information for designing skid trail systems that protect soil physical properties to maintain overall site productivity. The adverse effects of the extent and degree of soil disturbance can be controlled by operation constraints that include reducing tire pressure to the minimum allowable weight, installing larger diameter tires to increase the length of the machine footprint, increasing the number of axles or decreasing the number of equipment passes.