a b s t r a c tEcological restoration as a popular form of volunteer participation has been praised as an example of democratic natural resource management. However, the involvement of volunteers in projects guided by professionals does not necessarily ensure democratic knowledge exchange and production. Drawing insights from citizen science and political ecology, this paper investigates the role of science in mediating the dynamics between professional practitioners and volunteers. Using case studies of ecological restoration programs at two university arboreta in the American Midwest, this paper argues that the contrasting visions of science between professional practitioners and volunteers led to conflicts and presented challenges for the institutions to genuinely engage the public in contributing local knowledge and framing management priorities. While both groups emphasized the practical aspect of science in guiding restoration work, they differed in how they conceptualized the role of humans in restoration, work priorities, and how to apply scientific theories and methods in restoration. Moreover, at the university arboreta, science defined institutional identity and claims to scientific authority further delineated boundaries between professional practitioners and volunteers. As a result, distrust, tensions, lack of engagement, and different levels of desired public participation existed in these seemingly participatory programs. Theoretically, this paper contributes to the cross-fertilization between citizen science and political ecology by underscoring the politics of participation and the role of science (and its interpretations) in challenging expert-lay dynamics in environmental volunteering programs. Practical recommendations are included for deconstructing the expert-lay hierarchy and moving restoration toward a democratic practice.