افزایش ارزش بالقوه خدمات زیست محیطی در تالاب شهری: روش کشت و اکوسیستم

This paper proposes a three-tier process for supporting policy planning of urban agroecosystems. It comprises the following steps: (i) definition of the agro-environmental unit; (ii) measurement of the non-market values; (iii) estimation of opportunity cost. An application to an urban wetland agro-ecosystem within Mexico City is used for illustrating our methodology. We estimated that the wetland agro-ecosystem has a lower-bound monetary value between $15.6 million and $31.5 million USD/ha/y. As the land conversion rate is about 3.73 ha/y, the opportunity cost would be between $22,300 and $44,900 USD/ha/y. Such figures are an objective way to appreciate both the potential enhancement value and the opportunity cost of ecosystem services adjacent to urban areas, providing both urban and environmental policy guidance. We argue that this framework allows for multi-scale analysis and may be applied for other urban ecosystems as well.

Agro-ecosystems depend on natural environments from which productivity is enhanced in a sustainable way. In contrast to intensive agriculture, they provide not only food but ecosystem services as well (Porter et al., 2009, Sandhu et al., 2008 and Zhang et al., 2007). Most agro-ecosystems are either directly or indirectly linked to urban developments. Indeed, urbanization not only refers to increased paved area, but also implies higher demand for natural resources and ecosystem services. Yet, ecosystem services associated with agro-ecosystems or other modified landscapes are poorly understood (Sandhu et al., 2008).

The resulting estimates of ecosystem services monetary values are presented in Table 2. Market values ranged from $9,821.42 to $12,807.13 USD/ha/y and non-market values from $5,966.90 to $12,036.95 USD/ha/y. Grand total ranged from $15,788.32 to 24,844.08 USD/ha/y. The estimated economic value of Xochimilco’s agro-ecosystem services is within the range of previously estimated values elsewhere. For example, monetary use-values for Mexican wetlands in Campeche state mangroves have found to be about $2000 USD/ha/y (Lara-Dominguez, Yanez-Aranciba, & Seijo, 1998) and about $37,500 USD/ha/y for Gulf of California mangroves (Aburto-Oropeza et al., 2008). The monetary value estimated by Costanza et al. (1997) for global wetlands was $14,785.00 USD/ha/y. While no monetary estimates of ecosystem services in agro-ecosystems have been calculated in Mexico, a lower bound of $998 USD/ha/y is estimated by Porter et al. (2009) for cereal cultures in Denmark and a value of $19,420 USD/ha/y was found by Sandhu et al. (2008) for organic crops in New Zealand.