Aim. We analysed the spatial distribution patterns of plant species, in order to characterize the biogeographical structure of the French Mediterranean flora. Location. South of France (Languedoc-Roussillon and Provence-Alpes-C\^ote d'Azur) . Taxon. Vascular plants. Methods. We used a network approach to identify and characterize bioregions in southern France , based on a large database consisting in millions of geolocalized plant samples corresponding to more than 3,500 plant species. This methodology is performed following five steps, from the biogeographical bipartite network construction, to the identification of bioregions under the form of spatial network clusters , the analysis of their interactions and the identification of groups of plant species based on the species contribution to the biogeographical regions. Results. The French Mediterranean area is divided into eight statistically significant biogeographical regions that are highly connected spatially . Mediterranean and temperate sub-networks can be distinguished. The three mediterranean bioregions are share an important pool of species, and present a high spatial coherence. The limit formed closely matches the mesomediterranean thermoclimatic belt. The transition area between Mediterranean and temperate systems is represented by the bioregion "mediterranean border" whose northern limit fit the limit of the Mediterranean biome. Main conclusions. The proposed network approach provides a characterization of the biogeographical structure which confirms some previously recognized floristic regions in southern France, while providing more precise insights into the relationships between them . This approach sheds light on the historical and ecological mechanisms shaping the distribution of Mediterranean biota , and exemplify why fragmented distributions are common in the Mediterranean region  .
The delimitation of bioregions helps to understand historical and ecological drivers of species distribution. In this work, we performed a network analysis of the spatial distribution patterns of plants in south of France (Languedoc-Roussillon and Provence-Alpes-C\^ote d'Azur) to analyze the biogeographical structure of the French Mediterranean flora at different scales. We used a network approach to identify and characterize biogeographical regions , based on a large database containing 2.5 million of geolocalized plant records corresponding to more than 3500 plant species. This methodology is performed following five steps, from the biogeographical bipartite network construction, to the identification of biogeographical regions under the form of spatial network communities , the analysis of their interactions and the identification of clusters of plant species based on the species contribution to the biogeographical regions. First, we identified two sub-networks that distinguish Mediterranean and temperate biota. Then, we separated eight statistically significant bioregions that present a complex spatial structure. Some of them are spatially well delimited, and match with particular geological entities. On the other hand fuzzy transitions arise between adjacent bioregions that share a common geological setting, but are spread along a climatic gradient. The proposed network approach illustrates the biogeographical structure of the flora in southern France, and provides precise insights into the relationships between bioregions . This approach sheds light on ecological drivers shaping the distribution of Mediterranean biota : the interplay between a climatic gradient and geological substrate shapes biodiversity patterns. Finally this work exemplifies why fragmented distributions are common in the Mediterranean region , isolating groups of species that share a similar eco-evolutionary history .
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