عنوان مقاله [English]
Due to its multifunctional nature agriculture play important roles in ecological processes such as carbon sequestration, flood control, groundwater recharge, nutrient cycling, and purifying water, soil and air in addition to providing food, feed and fiber. These cover almost all ecological services provided by natural ecosystems, including provisioning services, regulating services, supporting services and cultural services (MEA, 2005). Provisioning services are the products obtained from ecosystems, including food, fiber and fuel. Regulating services are the benefits arising from the regulation of ecosystem processes, such as climate regulation, water purification, pollination and the control of pests and diseases. Cultural services are the non-material benefits people obtain from ecosystems, as spiritual enrichment, recreation and aesthetic experiences. Supporting services are those services necessary for the production of all other ecosystem services, such as soil formation and nutrient cycling (Norris et al., 2010). However, most of these services are not recognized and their values are hidden to the society. On the other hand, unlike natural ecosystems that only produce positive ecological services, agro-ecosystems also contribute to some negative externalities e.g. emission of greenhouse gases, leaching of chemicals into soil and water resources and reduction of biodiversity that should be taken into account (Norris et al., 2010). Economic valuation of these services makes them attractive for the society and policymakers to pay more attention towards conservation of ecosystem services. In Iran, studies on ecosystem services are scared and in global scale researches are mainly focused on natural ecosystems. In this study the economic value of ecological services as well as negative environmental externalities of wheat fields were estimated in the Khorasan Razavi province.
Materials and methods
Information was extracted from questionnaires collected from 40 fields varying in area, management and inputs level. Using these data economic value of feed and food, carbon sequestration, oxygen production, biodiversity, water retention and tourism together with greenhouse gas emission and nitrogen and phosphorous leakage as environmental externalities was quantified. Calculations were based on standard methods described by Millennium Ecosystem Assessment. Economic values were estimated as international dollar as proposed by De Groot et al. (2012) and reported as equivalent national price.
Results and discussion
The mean value of the total agroecosystem services of wheat fields excluding externalities, were estimated as 66.85×106 Rls.ha-1.y-1. The value of non-marketable services was 3.46 times more than food and feed and on average atmospheric services (oxygen production and carbon sequestration) contributed up to 62% of total value while biodiversity and provisional services included 9.3 and 21% of total, respectively and the other services below 5%. Net value of services was increased with increasing field size. However, doubling field size resulted in 50% increase in net value because larger fields were more intensified leading to higher negative impacts. Economic value of services was significantly dependent on wheat total dry matter and yield. Nonlinear relation was found between wheat yield and total value of services where a break point was found at yields above 4 t.ha-1. However, negative externalities were increased linearly with increasing both total dry matter and grain yield.
Results of this study indicated that despite to intensive management wheat production systems of Khorasan province are able to provide several regulating and supporting services and their economic value is 3-4 folds higher than provisional services harvested as grain and feed. However, negative externalities will be increased in more intensified fields with higher yield. Feeding a growing human population is obviously critically important and can only be done by recognizing and embracing the concept that food production systems are embedded within ecosystems. They depend on ecosystem services and have ecosystem impacts. Promotion of multifunctional characteristics of agroecosystems to maintain high yield together with ecological services, should be considered as an alternative for conventional management practices.