Investigating the effect of habitat amount and landscape heterogeneity on the gamma functional diversity of grassland and hedgerow plants

Abstract

Landscape structure is one of the main drivers of biodiversity, especially in agricultural landscapes. However, only a few studies explored its effect on the gamma functional diversity of plants. Yet, research questions at this scale are important to better understand and effectively preserve biodiversity. Using a large-scale sampling design with 30 landscape windows, we investigated the effects of habitat amount (i.e. grassland and hedgerow amounts), compositional heterogeneity (i.e. land use diversity) and configurational heterogeneity (i.e. land use spatial complexity) on the gamma functional diversity of plants in two habitat types: hedgerows and grasslands. We also investigated the same effects on the contribution of each functional trait related to different stages of the plant regeneration cycle to the overall functional diversity of plants. Habitat amount had contrasted effects on the functional diversity of both habitat types: a negative effect on grassland plant assemblages and a positive effect on hedgerow plant assemblages. Landscape heterogeneity only affected the functional diversity of hedgerow plants: configurational heterogeneity favoured functional dispersion but reduced functional evenness, and compositional heterogeneity affected trait contribution especially by shifting phenological and establishment strategies. Because they are linear habitats, hedgerows are indeed more likely to be influenced by edge effects than grasslands and thus displayed a strong response to landscape heterogeneity. Landscape variables influenced all stage of regeneration, and especially had a strong effect on traits related to establishment and dispersal. Synthesis. We demonstrated that landscape structure can both affect functional diversity and select particular trait syndromes related to plant dispersal, phenology and competitiveness. These results are important because they highlight that functional diversity must be studied at the gamma scale, to better understand the effects of land management and to preserve more effectively the associated ecosystem functioning.