Impact of different parts of skid trails on runoff and soil erosion in the Hyrcanian forest (northern Iran)

Abstract

Mechanical logging and skid trail construction in mountainous areas are associated with soil compaction and erosion risks. In this research, surface runoff and soil loss were studied at plot scale in different parts of skid trails in the Darab Kola mountain forests (northern Iran) using rainfall simulation experiments (20min at intensity of 54mmh−1). Rainfall simulations were carried on different parts of skid trails: [i] in the wheel tracks, [ii] in the central part between tracks, and [iii] in adjacent undisturbed forest floor as control. At each plot, 30 soil samples (0–20cm deep) were collected for physical and chemical characterizations.Although forest floor showed a relatively low response to simulated rainfall, results show that skid trails in the study area have a deep impact in the hydrological and erosional response of slopes at plot scale. Significant differences in runoff rates and soil erosion rates between wheel tracks/central parts of skid trails and undisturbed forest floor have been found. Although sediment concentration in runoff of skid trail parts was, on average, not different from that of forest soils, higher runoff rates in skid trail parts contribute to increase soil erosion risk. Soil texture and decreased bulk density, soil organic matter content and stability of aggregates are the main soil characteristics contributing to enhanced runoff generation and soil erosion risk in skid trails.Skid trails in the Darab Kola mountain forests are a source of sediments and runoff, which can cause in- and off-site impacts. Proper planning of forestry activities in the area should consider using erosion control measures in unpaved forest roads, especially in sensible forest areas and steep road segments. Insloping should help undisturbed forest soil areas to capture most of runoff flow and detached sediments, decreasing the severity of impacts in the study area.