Phylogenetic diversity of central-European urban plant communities: effects of alien species and habitat types

Urban habitats differ in their disturbance regimes, which act as an environmental filter determining plant community species composition. This is why plant communities in different urban habitats provide a suitable model for studying the effects of disturbance on phylogenetic diversity. We explore how phylogenetic diversity varies across urban plant communities and whether the introduction of alien species changes the phylogenetic diversity of resident communities of native species. In 32 cities in central Europe and Benelux countries we studied seven types of habitats subject to different disturbance regimes. Plots of 1 ha were sampled in each habitat by recording all spontaneously occurring species of vascular plants. A phylogenetic tree was constructed for all recorded species and phylogenetic diversity based on phylogenetic distances was calculated for each plot. A null model corresponding to random distribution of species on the phylogenetic tree was used to test whether phylogenetic diversity is non-random. Phylogenetic diversity was compared between the subsets of native and alien species, further divided into archaeophytes and neophytes. Phylogenetic diversity of plant communities in all the urban habitats studied was lower than in the null model. It varied with the disturbance regime in all the species subsets (native species, archaeophytes and neophytes). Introduction of alien species reduced phylogenetic diversity of the urban plant communities studied. Archaeophytes (widespread and common species that had enough time to spread to all suitable habitats) tended to decrease phylogenetic diversity more strongly than neophytes (often rare species which are still spreading and depend on dispersal vectors). Low phylogenetic diversity of disturbed plant communities in urban habitats probably results from strong environmental filtering, which selects species from a limited number of lineages that have traits that enable them to survive in disturbed habitats.