Sites side by side: Can an agglomeration bonus with an adjacency rule connect agri-environmental sites?

Many species need to cross landscapes for dispersal or seasonal migration. In view of the biodiversity crisis and increasing landscape fragmentation, incentives are needed to foster landscape connectivity and improve spatial coordination of protected sites across privately owned land. A large body of theoretical work and lab studies proposes that an agglomeration bonus could incentivize farmers to enroll adjacent fields to enhance landscape connectivity. This study empirically investigates a network bonus scheme in Switzerland with a dataset covering 322 program areas. In some program areas, farmers can receive the network bonus only if they are compliant with an adjacency rule of 100 m between sites, a policy that corresponds to an agglomeration bonus. In other areas, this rule does not apply, i.e. farmers can apply for the same bonus but irrespective of the location of their field vis-à-vis others. We empirically compare the impact of this policy with a double robust estimation. Counter to the expectations from the theoretical literature, our results show no impact of the agglomeration bonus on connectivity.