سود و زیان تجزیه و تحلیل حفظ زیستگاه ساحلی : روش ارزشگذاری مشروط تمایل به پذیرش / تمایل به پرداخت

The Contingent Valuation Method (CVM) was used to obtain the willingness to pay (WTP) of households in the contiguous area of the Garonne River near Toulouse, France, and the willingness to accept (WTA) of households that currently own land on the banks of the river to provide a strip of riparian land for habitat preservation. Results for the WTP study indicated a relatively large difference in WTP between open and closed ended responses. When corrected for the substantial number of 0 observations, the WTP was reduced by about half. The WTA results were constrained by relatively few positive responses. However, the value given by farmers who indicated a positive WTA appears consistent with revenues generated from crops. Moreover, many farmers who were already providing habitat preservation indicated a zero minimum WTA. Although the small number of WTA responses severely limits the ability to draw definitive conclusions, a comparison of the derived benefits (WTP) and costs (WTA) was made, which appeared to suggest the possibility of a favorable a benefit/cost ratio.

The United Nations conference at Rio de Janeiro in 1992 encouraged participating countries to combat environmental problems they face together, including global warming and forest, animal and plant preservation. Ecologists agree on the important role played by riparian forests along rivers. Riparian forests mitigate flooding, serve as temporary reservoirs, stock the water surplus the river is unable to evacuate at any given time, prevent bank erosion, improve water quality by filtering nitrates and other compounds from run-off, and preserve habitat for plant and animal species. At approximately the same time as the Rio conference, European Common Agricultural Policy attempted to incorporate environmental issues, such as reduction of pollution associated with farming practices, into policy. The reform was based on a system of direct payments to farmers to either reduce pollutants or to cease production on some land (Bonnieux and Rainelli, 1996). Whitby and Saunders (1996) reported on environmental protection and preservation using various contracting agreements in UK. In 1997, following the reform, a study was financed by the French Ministry of Environment to evaluate the costs and benefits of preserving riparian habitat on the banks of the Garonne River in the reaches near Toulouse, France (Amigues and Desaigues, 1999a). The wetlands adjacent to the Garonne River are under pressure from agriculture through erosion and irrigation. This area was chosen because it has been extensively studied by ecologists from the national center for scientific research (Descamps, 1987 and Descamps et al., 1998).

This study was undertaken with the primary purpose of assessing the welfare gains to the general population and welfare losses to landowners resulting from the implementation of a preservation program along the Garonne River. Several observations can be made. The WTP portion of the study reaffirmed the relatively large differences between open and closed ended question formats, with the former giving more conservative values, as well as an imbedding effect for a significant portion of the respondents. The importance of a post-response debriefing was also demonstrated. The WTA analysis provides some hope that the format can be effectively used to estimate welfare loss, particularly when the respondents have knowledge about market conditions similar to the hypothetical proposition, much as WTP studies have shown familiarity with markets yields more accurate WTP values. We are encouraged about the applicability of WTA contingent valuation under those circumstances. It is strongly recommended that face-to-face interviews and an in-depth debriefing of respondents be implemented for all WTA surveys to determine how WTA responses are formulated.