Historical continuity and spatial connectivity ensure hedgerows are effective corridors for forest plants: Evidence from the species–time–area relationship

摘要

Abstract Questions Are hedgerows efficient corridors for forest‐dwelling species within agricultural landscapes? Do time and space interact synergistically to enhance forest plant species accumulation in hedgerows (i.e. the species–time–area relationship)? Does the distribution profile of forest herbs along hedgerows differ between specialist and generalist species? Location Agricultural landscapes in northern France. Methods We assembled a chronosequence of 99 dated (1725–2008) hedgerows, which were surveyed for forest plant species and a number of local‐proximal descriptors. A subset of 29 hedgerows were further sampled for species occurrence data in 5‐m segments. We used generalized linear models to test the interaction between time (hedgerow age) and space on species richness. Space was characterized by both habitat size (hedgerow length, width and height) and spatial connectedness: i.e. whether a hedgerow is attached to a woodland and how much woodland habitat is available in the surroundings. We used generalized linear mixed‐effects models to test whether the probability of occurrence of forest herbs along hedgerows differ between specialists and generalists. Results Hedgerow age and length interacted synergistically to increase forest plant species richness. Hedgerows attached to woodlands hosted systematically more species. Taller and wider hedgerows with a lower intensity of adjacent land uses hosted more forest plant species. Increasing the spatial connectedness of hedgerows had a positive effect on the probability of occurrence of dispersal‐limited forest specialists in the understorey, which was not the case for generalists. Conclusion As predicted by the species–time–area relationship, ancient and long hedgerows attached to woodlands host more species and are more effective corridors. Creating new hedgerows to connect isolated woodlands can be a suitable strategy to restore functional connectivity, but it will be effective only in the longer term. The conservation of the most ancient hedgerows within intensively managed agricultural landscapes, especially those attached to ancient woodlands, should therefore be a priority.