In this research, one of the most important functions and services of the forest, the function of maintaining soil nutrients in the forests of the Dalab watershed in Ilam province, has been valued. First, the amount of erosion and sedimentation in the study area was checked using the modified MPSIAC model in the current condition. By developing two scenarios of converting the (current) natural forest with 30 to 50% canopy cover to bare land through scoring the model, the changes in the amount of erosion and sedimentation were estimated. Next, the amount of soil nutrients was determined by soil sampling and laboratory analysis. Then, taking into account the difference in the amount of erosion in the state of natural forest (current) with 30-50% canopy cover and bare land, the amount of each nutrient element in the soil, and the loss of soil nutrients was also calculated. Then, using the replacement cost method, the service value of forest ecosystem soil nutrient maintenance was estimated. The results showed that the studied forest can maintain 2.52 tons of phosphorus, 35.55 tons of potassium, and 251.96 tons of nitrogen per year with an approximate value of 2,275,700 million rials per year and prevent its loss due to erosion. Also, the value of each hectare of forest for this function was estimated at 88.13 million rials. The estimation of the value of this ecosystem service in Zagros forests indicates the very effective role of forest ecosystems in controlling erosion and protecting soil nutrients.

Forest machinery traffic on forests causes significant changes in increasing the bulk density, reducing porosity, ventilation and reducing water infiltration rate which resulted in an increasing surface runoff. According to the results of previous studies on the effect of mulch on reducing runoff in laboratory conditions, The aim of the present study was to determine and compare the amount of runoff produced in untreated skid trail, undisturbed forest (control area), and the skid trail plots covered by sawdust, under natural conditions in Namkhaneh District, Kheyrud Forest to find useful strategies to reduce the effects of forest utilization in order to maintain the function of forest water protection and reduce runoff. In this study, the runoff plots (6 m2) were triplicate established and runoff collected by pipes in the outlet plots were measured based on natural rainfall conditions. The results revealed that applying sawdust mulch to the skid trail decreased runoff compared to the untreated skid trail, and the runoff amount in undisturbed forest, untreated skid trail and sawdust mulch treatments were 0.40, 1.44 and 0.71 mm, respectively. The highest and the lowest amount of runoff were found for untreated skid trail and undisturbed forest treatments, respectively. Also, by application of sawdust mulch, the amount of runoff produced reduced by 48.4%, while the amount of runoff before the use of mulch in skid trail was 72.2% higher than the intact forest. Also, the runoff produced in skid trail control treatment was 51.1% higher compared to sawdust treatment.