Urban green spaces provide socially valuable ecosystem services. Through an historical analysis of the development of the National Urban Park (NUP) of Stockholm, we illustrate how the co-evolutionary process of humans and nature has resulted in the high level of biological diversity and associated recreational services found in the park. The ecological values of the area are generated in the cultural landscape. External pressures resulting in urban sprawl in the Stockholm metropolitan region increasingly challenge the capacity of the NUP to continue to generate valuable ecosystem services. Setting aside protected areas, without accounting for the role of human stewardship of the cultural landscape, will most likely fail. In a social inventory of the area, we identify 69 local user and interest groups currently involved in the NUP area. Of these, 25 are local stewardship associations that have a direct role in managing habitats within the park that sustain such services as recreational landscapes, seed dispersal, and pollination. We propose that incentives should be created to widen the current biodiversity management paradigm, and actively engage local stewardship associations in adaptive co-management processes of the park and surrounding green spaces.