Estimating the Amount of Runoff and Soil Erosion According to the Soil Properties and the Slope of the Skid Trails. Case Study: Loveh Forest, Golestan Province

Background: In recent decades, the escalating impacts of climate change, coupled with increasing anthropogenic pressures particularly in forest ecosystems-have raised significant concerns regarding the degradation of vital natural resources, such as soil and water.Among these pressures, logging operations, especially timber extraction via skid trails, result in substantial physical disturbances to the soil structure and surface hydrological behavior.These activities, create conditions conducive to enhanced surface erosion and runoff generation through soil compaction, reduction of vegetative cover, and increased effective slope.Hydrological and geomorphological processes, such as the transformation of rainfall into runoff and sediment transport, are strongly influenced by soil properties, slope gradient, rainfall intensity, and landuse practices.Consequently, examining both the individual and interactive effects of these factors, particularly in ecologically sensitive forested regions, is essential for formulating sustainable land management strategies.This study aims to quantitatively and qualitatively assess the influence of soil properties and slope gradients on runoff generation, sediment yield, and rill erosion along skid trails in Compartments 106 and 107 of the Loohe Forest Management Plan in northern Iran.The research endeavors to enhance our understanding of the environmental implications of timber extraction and provide a scientific foundation for the sustainable management of soil and water resources.Methods: To meet the study objectives, the skid trails were categorized into five slope classes: less than 5%, 5-10%, 10-15%, 15-20%, and 20-25%.Three treatment types: (1) wheel track (machinery path), (2) trail centerline, and (3) undisturbed control area (natural forest without anthropogenic interference) were identified within each slope class.Soil samples were collected at three depths (0-10 cm, 10-20 cm, and 20-30 cm) from each treatment using steel cylinders.Physical soil parameters, including texture, bulk density, porosity, and gravimetric moisture content, as well as chemical properties (such as organic matter content and electrical conductivity), were analyzed in this research.To simulate hydrological processes, a rainfall simulator was employed to deliver precipitation at an intensity of 65 mm/h for 30 min, reflecting a 10-year return interval for the region.Hydrological and erosional variables, including runoff volume, time to runoff initiation, runoff coefficient, sediment concentration and yield, and rill dimensions (depth and width), were measured and recorded after simulated rainfall application.Statistical analysis of the data was conducted using the Analysis of Variance (ANOVA) and mean comparison tests at a 5% significance level to evaluate both main and interaction effects.Results: The results indicated statistically significant differences (p < 0.05) among treatments (wheel track, trail center, and control) and slope classes for most of the measured variables, including runoff volume, sediment yield and concentration, runoff coefficient, runoff initiation time, and rill erosion intensity.The highest values of runoff and sediment yield were recorded in the wheel track treatment, identified as the most compacted and disturbed area due to repeated machinery traffic, particularly on slopes exceeding 20%.In contrast, the control plots, characterized by natural vegetation and the absence of mechanical disturbance, exhibited the lowest values across all variables.Soil compaction in the wheel tracks, evidenced by increased bulk density and reduced porosity, resulted in a marked decrease in infiltration capacity, thereby promoting increased surface runoff.The interaction between soil properties and slope gradient significantly influenced the hydrological and erosional responses; steeper slopes amplified the negative effects of soil compaction on runoff and sediment production.