Landscape scale patterns of alien plant species on coastal dunes. The case of iceplant in central Italy

Question: We investigate the spatial pattern of coastal landscapes invaded by iceplant focusing on two questions: I) How is the spatial structure of iceplant patches? Does it differ from native costal dune cover types; II) How are iceplant patches distributed with respect to other cover types? Location: Tyrrhenian coast of Central Italy. Method: On the basis of a detailed land cover map we calculated structural metrics for each natural coastal dune cover category (Mean Patch Size and Patch Shape index). In order to asses the spatial association between iceplant patches and the different cover types we implemented an electivity analysis. Results: The mapped coastal dune cover types can be related to beaches, dunes and sand plains variants. These coastal dune cover types can be related to the typical Tyrrhenian coastal dune vegetation zonation. Iceplant dominated vegetation presents elongated and irregularly shaped patches, which are not significantly different from most of the natural cover types suggesting a natural spread along the analyzed territory. Iceplant patches are positively associated with beach, mobile and inter-dune cover types suggesting that these habitats as particularly exposed to further alien spread. Iceplant patches are also positively associated with artificial surfaces highlighting this cover type as possible source of propagule pressure. Conclusions: The proposed landscape approach combining patch-based metrics with edge-based metrics provided a comprehensive description of the invaded coastal landscape. From an applied research perspective, this landscape approach could be useful to identify the correct strategies to manage alien invaded areas.