A large-scale assessment of Isoetes histrix s.l. swards in the Mediterranean basin

One of the most vulnerable community types in the Mediterranean basin are the Isoetes histrix swards. The present study, based on a literature review, was aimed to define patterns of plant communities with I. histrix and to identify the key factors driving these patterns at large spatial scale. Data from 7 areas (Corsica, Crete, Italian peninsula, Portugal, Sardinia, Spain, and Tunisia) were assembled into a composite matrix including 255 surveys and 314 species. To each survey the following abiotic variables were associated: geographic position, elevation, distance from the sea, annual precipitation, average annual temperature, and substrate type. Exploratory analysis reveals extremely high beta diversity among and within the localities, which calls for protection measures to be taken individually in each area. The most influential abiotic factor explaining this diversity is precipitation, which necessitates special management plans to maintain the hydrological status of each site. The fact that precipitation, a relatively unpredictable and unstable climatic variable is most influential, confirms that the isoetid communities of the Mediterranean region are vulnerable to climatic changes.