5. Conclusion
Despite the economic rationale and some enthusiasm for integrating ecosystem services into environmental management, efforts to roll out PES have largely met with frustration. Researchers and practitioners have found it difficult to demonstrate the validity of the original conception of PES that focused on free-market exchanges. PES is now increasingly understood as an open and flexible concept that involves different types of incentive-based policy instruments. The success of PES, therefore, relies not only on market mechanisms, but also on socioeconomic and institutional conditions that make it possible to overcome these constraints. Under the newly relaxed specification of PES, the identification of such conditions becomes one of the key tasks for PES researchers and practitioners. Our study makes a contribution by highlighting one important favorable condition for PES: wealth disparity between ecosystem services buyer and sellers. We do not regard this structural factor as necessary or sufficient, but we believe it is important for understanding performance of PES and for assessing the suitability and design of PES. The results of our analysis speak to a pragmatic approach to advancing environmental conservation and economic welfare. These insights can help policy makers and environmental management professionals to target PES programs toward suitable regions and populations, thereby increasing chances for success. After all, ecosystem services are not ordinary market goods, so their exchange demands unconventional market mechanisms.
