Plot-Scale Effects of Ground-Based Skidding on Runoff and Soil Loss in Relation to Slopes and Leaf-On and Leaf-Off Periods in the Mixed Broadleaf Forests

Soil compaction and loss of surface litter from skid trails reduced the water absorption capacity in mineral soils, which reduced water infiltration and increased runoff, which then caused surface erosion. We hypothesized that ground-based skidding, different slope angle classes (0–20% and 20–40%), and forest canopy cover (leaf-on and leaf-off period) would be significantly effect on runoff and sediment loss. In order to measure the total runoff and the sediment loss, quadruplicate bounded runoff plot (2 m2) was established on the skidding and the control sites, and two different slope angle classes on each site (totally 16 runoff plots with 20 rainfall events) in the Gorazbon district in Hyrcanian deciduous forests following Timberjack 450C skidding operations (32 machine passes) over one-year. The natural rainfalls were measured due to get more useful data. The skidding and the leaf-on and leaf-off period had statistically significant effects on runoff and sediments (P < 0.05). There was a statistically significant difference between runoff and sediment loss in different leaf-on and leaf-off periods, with leaf-off period having the highest sediment loss, while the leaf-on period had the least. The slope angle classes and its interactions had no significant effect on runoff and sediment loss. The highest runoff of just over 1.6 mm was from a skid trail with a 20–40% slope in the leaf-off period, and the highest sediment production was 6.95 g in the skid trail with a 20–40% slope in the leaf-off period. In the Hyrcanian deciduous forest, fallen leaves (leaf-off period) were coincided with the highest and most erosive rainfall, which resulted in an increase in runoff and sediment yield.