Effect of vegetation cover percentage on runoff and soil loss of interill erosion in forest road cutslope (Case study: Kohmiyan Forest, Azadshahr)

Roads provide access to forest resources for properly management of timber production, transportation, forest protection and ecotourism. Also, forest roads are known as one of the main sources of sediment production in forest watersheds. Globally, soil erosion is one of the most important environmental problems which is threaten soil and water resources. Therefore, it is necessary to investigate on soil erosion of forest roads and determination of its quantity rate. The measurement of soil erosion rates under natural rainfall conditions is costly and time consuming. Data provided by rainfall simulation and static site measurements can be used to predict erosion rates under natural conditions, especially for erosion rates from forest roads. Various studies were investigated the factors affecting water erosion in forest roads and their results had shown a significant correlation among slope percentage, vegetation cover percentage, climate, Physical and chemical soil characteristics, road traffic with the amount of soil erosion. This study, specifically, aimed to assess the effect of vegetation cover on soil erosion, runoff production and sedimentation.
This study was done to investigate the effects of vegetation cover of cut-slope forest road on erosion variables such as runoff amount, sediment concentration, soil loss, time to runoff and runoff coefficient in Kohmiyan Forest of Azadshahr. It was conducted five treatments of vegetation cover including 0, The results indicated that the average amount of runoff in five levels of vegetation cover including bare ground, less than 25%, 25-50%, 50-75% and 75-100% were 24.7,17.82, 12.78, 5.23 and 2.64 l/m2, average amount of sediment concentration were 15.66, 9.41, 7.37, 5.07 and 2.39 g/l and average time of runoff were 12.00,75.00, 150.00, 238.75 and 365.75 and runoff coefficient were 47.8, 35.62, 25.71, 10.58 and 5.27 percent, respectively. The results statistically showed significant differences between amount of runoff and soil loss due to vegetation cover of road cut-slope. The results of Tukey test indicated significant differences among mean runoff and sediment of five level and decrease with increased road cut-slope of vegetation cover percentage.
The effect of vegetation cover on the cut-slope road is completely significant on the amount of runoff, sediment concentration, soil loss, time to runoff and runoff coefficient. In other words, the amount of runoff and soil loss has a reverse and significant relationship with vegetation cover percentage. Vegetation cover percentage has had a positive impact and role in the reduction of the amount of runoff and sediment in the forest roads.