Estimating the economic value of the role of vegetation in controlling soil erosion (Case Study: Kechik Watershed)

Preservation of soil and prevention of occurrence and intensification of erosion are the most important functions of natural ecosystems. This issue is especially important in steep and mountainous areas. Soil conservation function, like many other ecosystem services, lacks a market to determine value. Natural ecosystems are one of the important economic resource for many developing countries that contribute to the development of regions and communities by producing goods and services. This study was conducted in 2019 with the aim of investigating the role of natural ecosystem in Kechik area in controlling soil erosion and determining the economic value of soil protection based on soil fertility maintenance function.

In order to estimate soil erosion quantitatively , the RUSLE model, which inputs include rain erosion factor, soil erodibility factor, length and degree of slope factor, vegetation factor and protective operations factor, was used in GIS environment. To calculate the economic value of soil fertility maintenance function, soil retention and soil nutrient content including nitrogen, phosphorus and potassium in the area were estimated and its economic value was calculated using the alternative cost approach.

The results of soil erosion by RUSLE method showed that the range of soil erosion in the region varied between 0 to 239.2 tons per hectare per year and its average was estimated at 7.94 tons per hectare per year. The value of the main elements preserved in the soil of the whole basin was equal to 9.21 billion Rials per year and the value of each hectare of the region's ecosystem was estimated at 2.55 million Rials per year. Also, the analysis of erosion data in IDRISI Selva software showed that the factor of length and degree of slope with a correlation coefficient of 93% and a coefficient of determination (R2) of 0.87 had the greatest effect on estimating annual soil erosion.

The result of this study states that the value obtained per hectare of forest is 3.39, rangeland 2.84 and dry land 2.16 million rials per year, which shows the more value of rangeland ecosystem than dry lands. Due to the positive effects of vegetation, the need for special attention to rangeland and forest vegetation to reduce soil erosion is felt and it is recommended that biological and soil protection programs to reduce soil erosion damage in areas with high erosion sensitivity in the region.