Shoja Ramin, MSc

Forest operations can lead to increased runoff and soil loss on roads and skid trails. The aim of this study was to evaluate the effectiveness of two erosion control treatments applied to different segments of skid trails following six natural rainfall events. A total of 162 plots 10 m long by 4 m wide were established in a Hyrcanian deciduous forest to assess soil runoff and soil loss following ground-based harvesting traffic. The experimental setup consisted of three levels of traffic intensity (three, eight and 16 skidder passes), two levels of slope gradient (≤20% and >20%), three classes of curvature (narrow = high deflection angle, 60°–70°; wide = low deflection angle, 110°–130°, and straight trail segments), and three classes of mulch cover (bare soil, sawdust cover, and rice straw cover). Each treatment combination was replicated three times, yielding 972 soil samples. The average surface runoff volume and soil loss differed significantly between the switchbacks and the straight trail segments and depended strongly on the degree of curvature, with severity of adverse effects increasing with curve tightness. Mulch cover treatments had a significant ameliorating effect on the surface runoff volume and soil loss throughout the skid trail. The average runoff and soil loss from the skid trails treated with sawdust cover (SC) (0.24 g m-2 (mm) and 0.49 g m-2, respectively) were lower than on trails covered with rice straw (RSC) (0.45 g m-2 and 1.19 g m-2, respectively), which were, in turn lower than on untreated bare soil (BS) trail segments (0.70 g m-2 and 2.31 g m-2, respectively). Surface runoff volume was significantly positively correlated with soil loss and both were positively correlated with dry bulk density and rut depth and negatively correlated with litter mass, total porosity, and macroporosity. Surface cover is a successful measure for controlling erosion losses following skidding disturbances, particularly in the switchback curves of trails on steep slopes where erosion potential is high.