Finding the right balance of conservation effort in cultivated grasslands: A modelling study on protecting dispersers in a climatically changing and anthropogenically disturbed environment

Managing cultivated grasslands in a sustainable way is controversial, because it often goes along with economical loss and additional effort for local farmers. On the plus side, such a management could permit inhabiting species not only to survive but to thrive and expand their range. In order to satisfy both aspects, it can be helpful to minimize conservation effort to a degree that is still ecologically beneficial but intervenes as little as possible with regional land-use customs. Computer simulations are a useful tool to find such compromises prior to implementing management strategies. We simulated the population development of the large marsh grasshopper, a grassland species with limited dispersal abilities, in a disturbed and climatically changing environment of Germany up to the year 2080. Our results show that - in a spatially aggregated landscape - adapting the harvesting schedule in a relatively low number ≤ 7 % of (in)directly connected yet otherwise intensively managed grasslands suffices for species preservation and even expansion to some extent. The effect on dispersal success of additional conservation effort above this 7 % threshold is significantly lower than it is below the threshold. In terms of population size, however, every additional refuge benefits the grasshopper. Climate change enhances the positive effects on the target species even further. A higher level of fragmentation, however, requires a substantially larger conservation effort in terms of protected grassland proportion. Therefore, it is recommended and more effective to focus on the implementation of protected areas within spatially aggregated grasslands. Stakeholders should additionally be aware of the fact that it can take several years for a conservation effort to become apparent and measurable, especially if the goal is to support an isolated or reintroduced species in expanding into unpopulated territories.