While this is interesting in-and-of itself, it would also have been interesting if the studies had provided information on the average payment/unit measured (e.g. hectare or type of ecosystem service) for each of the PES schemes, and if possible, information on the opportunity costs of land. To some extent this also raises the question of associated monitoring and enforcement efforts across protected areas. It would be interesting, for example, to better understand if the results depend on the average PA spending per hectare.