Motivational crowding describes the phenomenon that external monetary incentives can undermine non-monetary, intrinsic motivations to engage in the promoted behaviour. While such crowding effects have been observed and discussed for a wide array of human behaviours (Frey and Jegen 2001; Gneezy, Meier, and Rey-Biel 2011), they have emerged as a key criticism of Payment for Ecosystem Services (PES) (Rode, Gómez-Baggethun, and Krause 2015; Akers and Yasué 2019; Ezzine-de-Blas, Corbera, and Lapeyre 2019).
