The tragedy of the commons is known from both institutional economics as well as in biology and used to describe the long term decline of common pool resources as a consequence of opportunistic behaviour of individual users. A whole body of knowledge addresses the design and implementation of particular institutions to tackle this problem.
In his PhD thesis, Jan Jansen presents the concept of commons as a new way to approach the governance of Natura 2000 sites. Based upon a extensive and thorough study of vegetation changes in relation to changing land use activities in the Serra da Estrela (Portugal) he shows the importance of extensive agricultural activities for the preservation Natura 2000 habitat types. The conservation of several habitats in the Serra da Estrala might become problematic in the near future due to land abandonment. A collaboration between new and old stakeholders, addressing the site as a common pool resource providing various ecosystem services, might create the opportunity to realise Natura 2000 objectives as part of a new economic management of the area.