Relationships between native and alien vascular flora and landscape complexity in the province of Padova (North Italy)

Landscape complexity is the basis of species diversity at regional scale. The arrangement of ecosystems in a landscape mosaic in space and time changes as a result of human pressure. This landscape mosaic may either be simplified or complicated by urbanization. Therefore, human pressure has a multi-faceted influence on richness and composition of vascular species. In this study, we investigated the relationships between landscape complexity and native and alien vascular flora in the entire province of Padova, North Italy (2,144 km2), over an atlas map composed by 81 squares of 25 km2. The data, presence or absence of vascular species in each square, have been collected over several years, through excursions conducted by experienced botanists and have been recently stored in a geospatial vector database. Landscape complexity was calculated with the Shannon diversity index, using the proportion of the first level Corine Land Cover types. Each square was partitioned into subsets of landscape types identified through a hierarchical agglomerative clustering with Corine Land Cover proportions. Then, we performed an IndVal analysis to assess the degree of association of each species to each subset. We used the LecoS plugin for the QGIS geographical information system to calculate the landscape metrics and the R software for the statistical analyses. The alien flora showed a pattern of distribution similar to the native flora. As expected, the species richness in the hilly semi-natural areas was higher than in the agricultural-based urban plain. In the plain, species richness increased with increasing cover of artificial surfaces and decreased with increasing cover of agricultural areas. Landscape complexity has proven to be a good predictor of changes in the species richness. About fifty species were associated to some of these landscape types. The occurrence of some species at local scale was a reliable indicator of larger scale landscape patterns. The variety of ecological attitudes of the alien species was one of the reasons for their widespread distribution regardless the landscape type. Landscape complexity was an additional determinant factor, which did not discriminate between native and alien species. We conclude that in the province of Padova distributional data of plants obtained from flora atlases at good resolutions help the identification of landscape emergent properties.