Anthropogenic disturbance and alien plant invasion drive the phylogenetic impoverishment in riparian vegetation

Anthropization worldwide is increasingly homogenizing biodiversity, i.e., impoverishment of phylogenetic and functional diversity. This study aimed to assess plant phylogenetic relationships of riparian communities in anthropogenically disturbed and undisturbed sites across Continental Portugal. For the analyses, we used 947 species distributed in 205 undisturbed sites and 180 disturbed sites sampled in 100 m plots distributed throughout the country. Then, we assessed the phylogenetic diversity and structure, evolutionary distinctiveness (ED), and conservation of functional traits (life forms) and geographic origin (alien or native) in each site. Our findings. Indicated a higher phylogenetic diversity (higher scores for PD, MPD, MNTD and their standardized effect size) and ED in the undisturbed sites compared to the disturbed ones. The lower phylogenetic diversity in the disturbed sites also relates to the phylogenetic conservatism we found for the lineages of alien and hydrophyte species, which increases the diversity homogenization in those sites. On the other hand, we also recorded higher aliens’ ED for the undisturbed sites. Based on the results, we conclude that although the undisturbed sites still harbor higher phylogenetic diversity, they also require monitoring to track the spread of alien species from phylogenetic distant lineages (i.e., high ED) that might thrive in the native communities.