Species and functional plant diversity in a heavily impacted riverscape: Implications for threatened hydro-hygrophilous flora conservation

In this framework, a floristic study was performed to clarify the patterns of species and functional plant diversity with respect to the origin, hydrology and structural complexity of 60 marginal habitats within the watershed of the Oglio River (3800 km2, Northern Italy). The basin of this regulated river is heavily exploited by intensive agriculture and farming, occurring over 75% of the surface; wetland habitats occupy small surfaces, generally of a few hectares, and are scattered in the territory. The sampled plants were classified by life-growth form and were grouped into four clusters representing the main hydro-hygrophilous functional zones of investigated habitats. An appreciable regional diversity (208 taxa) was found. The typical floristic contingent was composed by lemnids, large helophytes and semi-hygrophilous opportunist species. Experimental data revealed: (i) the predominance of terrestrial species within shallow aquatic habitats of the Oglio riverscape and (ii) the deterioration of the obligate aquatic plant contingent and the helophyte representativeness in riparian zones. Overall, plant diversity appears to be driven more by the sites origin (natural vs. artificial) and their structural complexity rather than by their hydrological features (lentic vs. lotic). On the other hand, the present data confirm the important role of the artificial drainage system as temporary valuable habitat for lowland macrophytes.