Influence of bedrock-alluvial transition on plant species distribution along a Mediterranean river corridor

The variation of riparian plant species composition along a river according to lithological features, forming more or less discrete plant assemblages, was tested using multivariate and univariate analyses. Moreover, Sørensen’s index was applied to examine similarity between geological and floristic groups, and the Wilson–Shmida index to investigate species turnover. The analyses were based on field data recorded along a Mediterranean river (Rio Santa Lucia, Sardinia, Italy), where the morphology is influenced by the bedrock-alluvial transition. The results obtained from the various analytical techniques were in close agreement, and underlined that the lithological types exerted an important influence on the distribution and richness (peak in the medium and the upper river part) of riparian plants, but also in their life forms (woody species and hemicryptophytes). The distribution patterns of species along the river suggested that primary drivers in the organization of the riparian plant communities were lithological types, geomorphology and altitude. Moreover, the bedrock-alluvial transition marked the highest species turnover, linked also to a different degree of human disturbance. The results of the present study indicate that the bedrock/alluvial influence is an integral component of the patch structure, which strongly influences riparian plant distribution patterns in a Mediterranean environment.