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In the Mediterranean region, the majority of watercourses have undergone hydrogeomorphic alterations, mainly due to flow regulation such as damming. Despite this, few investigations analyzing dam impact on upstream river vegetation exist. In this study, we analyzed the temporal vegetation changes occurring along the Tiber River in Nazzano (Rome), as a consequence of the construction of a dam in 1956. We examined which communities are more sensitive to this anthropic alteration of the river ecosystem. An evaluation of how and with what timing these communities varied their extension as a result of such alteration is provided. Moreover, the role of the hydrogeomorphic alterations on the evolution of the river vegetation, linked to the management of this dam as a run-of-the-river impoundment, was analyzed. Our results show the main vegetation changes occurred during the first decades after the dam construction. Indeed, the dam operation caused significant local expansion of the upstream river waters, causing the flooding of most of the surrounding lands, and the formation of new sub-lentic wetlands. The altered hydrogeomorphic conditions favored the development of natural riparian and macrophyte communities typical of lacustrine ecosystems and therefore mostly different from those expected for the analyzed river typology. The changes in extension over time of these vegetation communities highlight their close relation to the alteration of some hydrological parameters especially affecting the river water level.

Astragalus exscapusL. subsp.exscapus(Fabaceae) is a rare and declining perennial herb with a very fragmented distribution range. It is interpreted as a relict of the glacial steppe flora. In Italy, it was known until now only from the Alpine “dry valleys”, namely from Val d’Aosta and Val Venosta/Vinschgau. We report on the discovery of a population on the slopes of the Fucino basin in the Central Apennines (Abruzzo, Italy). The finding significantly expands the known species range (the site is >600 km away from the nearest known populations), suggesting that during Pleistocene steppic phases it had a wide distribution across Europe.A. exscapusadds to a number of other steppic relicts found in the Fucino basin, highlighting that some inner valleys of the Central Apennines, featuring a relatively continental climate, perform as “interglacial refugia” for the steppe flora. Further research is needed to ascertain the species’ local distribution and abundance, and to clarify its vicariance history; however, the finding underlines the need to re-evaluate priorities in landscape management, as in the Apennines dry grasslands are often given low values compared to forests and are frequently destroyed by afforestation practices with non-native conifers. [ABSTRACT FROM PUBLISHER]

Plant diversity measures (e.g., alpha- and beta-diversity) provide the basis for a number of ecological indication and monitoring methods. These measures are based on species counts in sampling units (plots or quadrats). However, there are two alternative conventions for defining a vascular plant species as “present” in a plot, i.e. “shoot presence” (a species is recorded if the vertical projection of any above-ground part falls within the plot) and “rooted presence” (a species is recorded only when an individual is rooted inside the plot). Very few studies addressed the effects of the two sampling conventions on species richness and diversity indices. We sampled mountain dry grasslands in Italy across different plot sizes and vegetation types to assess how large is the difference in alpha- and beta-diversity values and in sample-based rarefaction curves between the two methods. We found that the difference is greatly dependent on plot size, being more relevant, both in absolute and percentage values, at smaller grain; it is also dependent on habitat type, being larger in shallow-soil communities, as they have a sparser vegetation structure and host life-form types with a larger lateral spread. At fine spatial scales (<1 m 2 ) the difference is large enough to bias statistical inference, and we conclude that at such scales one should not attempt to compare plant diversity indices if they were not obtained with the same sampling convention. [ABSTRACT FROM AUTHOR]