Using process-based indicator species to evaluate ecological corridors in fragmented landscapes

Increasing connectivity among habitat patches is assumed to mitigate the effects of fragmentation on biodiversity, leading to the emergence of green and blue infrastructures in public policies as corridors facilitating movements of species within fragmented landscapes. But still, the scientific knowledge and tools for identifying critical features that make a corridor efficient for biodiversity conservation, and for guiding their establishment and management are still scarce. Here, we define three types of indicator species based on their ecological requirements and dispersal traits in the context of forest metacommunities embedded into agricultural landscapes in N France. We then evaluate whether hedgerows can act as corridors for forest herb species and if this can be predicted from the occurrence of the selected indicator species. We show that among each socio-ecological group of forest herb species, (i) the best disperser (“scout” species) indicates habitat suitability for the other species of the group, hence predicts a colonization credit; (ii) the species with intermediate dispersal traits (“median” species) indicates forest species richness and composition of a given hedgerow. In contrast, the worst dispersers (“focal” species) have a low indicator power, as a probable consequence of extinction events occurring in hedgerows, where ecological conditions are suboptimal with respect of forest species. The quality of the corridor increases with the width, height and age of hedgerows, but decreases with increasing land use intensity in adjacent lands. We conclude that process-based indicator species can be valuable tools to assess the efficiency of ecological corridors in fragmented landscapes.