BRIDGE

Building a bridge between river corridors, roadsides and field margins: how landscape interactions modulate taxonomic and functional plant diversity

BRIDGE aimed to understand how riparian corridors, road corridors and field crop margins shape both taxonomic and functional plant diversity across agricultural landscapes. We compared such landscape patterns from Spain, France and United Kingdom. The first task was devoted to build a homogenised database including 11,400 samples, more than 3,000 species and related environmental variables and biological traits. In the second task, we first highlighted the ecological effects of road-river intersections (bridges) on plant communities. The alteration of plant diversity is significant at bridges compared to reference sites. However, bridges had no effect on the percentage of native and non-native species, nor were there differences between bridge and reference quadrats in the community-weighted mean (CWM) of invasive versus non-invasive status. The use of specific spatialized models showed that this effect was local and that non-directional (across landscape) factors influenced more plant diversity than directional (within-corridor) ones. Physical disturbance (transverse gradient) played also an important role in shaping diversity. . Then we estimated the importance of the species shared among the three linear habitats and inferred their role in shaping both functional and taxonomic diversity. The three habitats share 30% of the total number of species. Riparian species host the highest number of species (gamma diversity) and the highest proportion of specialists, while roads and field margins shared the highest number of indicator species. Traits related to disturbance, soil moisture and nutrient loads explained the differences in functional diversity. Hypervolume analysis showed that habitat heterogeneity and near-natural disturbance explain the broader functional space of riparian corridors. A more specific ongoing work is targeting the effects of local and regional factors on introduced species. In a fourth task, we drawn some management implications of this project, suggesting that: i) interactions among linear habitats should be included in management strategies and ii) the studied habitats include both good (refugia for threatened or keystone species) and bad (invasion by exotic species) aspects, that should be mitigated, especially in the scope of climate change.