Uncertainties in demonstrating environmental benefits of payments for ecosystem services

Payments for Ecosystem Services (PES) have become the flagship of conservation organizations in recent years. However, PES schemes are as much criticized as they are acclaimed in the literature. Researchers have pointed that many PES schemes, particularly water-related ones, are based on unreliable assumptions and lack strong causal links between land use and ecosystem services. Evidence of outcomes is hardly demonstrated. This uncertainty in PES schemes arises not only from practical difficulties, but from the complexity of the human-environment systems (HES), and the limits of current knowledge about HES. Many scientists and practitioners have proposed that more research is needed to improve the scientific basis of PES. Here we argue that this research should be complemented with a deeper understanding of the uncertainties involved in PES, an explicit treatment of these in the whole process of PES negotiation, design and monitoring, and clear uncertainty communication among the actors involved. Neglecting uncertainties could lead to unfounded expectations and poor assessments of PES outcomes. If recognizing and accounting for uncertainties are to threaten the success of PES, then uncertainty can be seen as an opportunity to open up the dialogue to alternative ways of achieving the desired conservation goals.