Assessment of the soil-protecting services of the forest ecosystem: a case study in Ilam catchment, Iran

The natural forests of western Iran play a key role in delivering services and goods to local society. Nonetheless, this forest ecosystem, despite its importance, is threatened by natural factors and anthropogenic activities, resulting in decreasing soil quality and soil erosion. The present research aimed to assess the effects of the forest ecosystems on soil erosion control in Ilam catchment in southwest Iran. For this purpose, after estimating the soil loss in natural conditions (NC), we predicted the amount of soil erosion under two scenarios: (i) convert natural forest with 20% canopy cover to destructed forest with 0% canopy cover (SC.1), (ii) increase forest cover by 40% (SC.2). Our results indicate that the estimated mean soil erosion was within the range of 9.36 t ha^-1 yr^-1 in irrigated and garden use to about 256 t ha^-1 yr^-1 in bare soils under NC. We found that when converting natural forest to destructed forest, the mean annual soil erosion rate increased 105.75 t ha^-1 yr^-1, 118.1 t ha^-1 yr^-1, and 19.57 t ha^-1 yr^-1 in the dense forest, sparse forest, and Agri-Forest use, respectively. These results show the protective effect of the forest against soil erosion.