Negative impacts of nomadic livestock grazing on common rangelands' function in soil and water conservation

摘要

There is a great deal of pressure on common rangelands through excessive usage of forage resources. It brings private benefits for local communities while imposing ecological and economic damages to ecosystem services as community products. This is evident especially in arid environments where ecosystems are often in poor conditions. Khafr and Sivar rangelands were selected in central regions of Iran to calculate the external costs caused by ecosystem service loss due to nomadic utilisation system. Water and soil conservation services were considered in this study as two major ecosystem services provided by rangeland ecosystems. The impacts of nomadic livestock grazing on soil conservation service was determined by estimating soil erosion in pre and post grazing conditions using MPSIAC model and the impacts on water conservation function was evaluated by calculating the runoff volume before and after grazing through the empirical CN method. The economic value of these ecosystem services was estimated using replacement cost approach. Direct benefits of nomads from livestock grazing was studied using a questionnaire-based approach and structured questionnaires. Economic justification of this utilisation system was revised finally considering the economic damages to ecosystem services as external costs. Results showed that ecosystem service losses as hidden social costs are significant under the current utilisation system. The annual damage to water and soil conservation services was 794,839 US$, as part of the negative externalities of the nomads. Meanwhile, the annual net present value of direct benefits of nomadic livestock grazing were only 601,562 US$, and combining annual external costs with the private costs reduced the net present value of the system to - 193,276 US$ per year. As a conclusion, it should be noted that contrary to the importance of the nomadic system from cultural and social aspects, the current system is not economically justified in arid, poor and common rangelands. This highlights the need for appropriate policy to maintain both ecological and socio-cultural values.