How do different levels of individual payments for environmental services (PES) affect intrinsic and social motivations for forest conservation? Does introducing small PES crowd out these motivations? This paper presents findings from framed field experiments (FFE) conducted with local forest users in Tanzania. The payoff structure represents a common-pool resource situation; participants' payoffs depend on the number of trees harvested, and aggregate over-harvesting can harm future harvest. Four levels of individual PES are tested in a between-group design: no (0%), low (20%), medium (60%) and full (100%) PES, where the level is relative to the harvest value. We observe lower than theoretically predicted harvest rates at no, low and medium PES, while the opposite is true at full PES. The results suggest that low PES has little impact on local forest use in Tanzania and has on aggregate no significant effect on intrinsic and social motivations. Increasing payments has a negative, but diminishing effect on harvest rates.