The phytocoenosis of consolidated alluvium: a syntaxonomical and synecological study in the braided streams of southern Tuscany (Italy)

The outer terraces of braided streams of southern Tuscany consist of con solidated detritus, often with a thin layer of humus. In these a new association of the alliance Bromion erecti (Seselio tortuosi-Brometum erecti) and fragments of Coronillo valentinae Ampelodesmetum (Oleo-Ceratonion), a thermo-xerophilous Ampelodesmos mauritanicus community, are recognized. The association Seselio-Brometum erecti is widespread on the inner sites and is characterized by a group of relatively mesophilous species. On the contrary, the Ampelodesmos mauritanicus communities are found along subcoastal water courses char acterized by several Stenomediterranean species. Both these hemicryptophyte coenoses are ecologically and floristically distinct from Santolino etruscae-Saturejetum montanae s.l. which includes the chamaephyte communities of the lower terraces. Statistical analysis are shown that the main abiotic factors affecting the pattern of riparian vegetation in these sites are height and distance from running water, and to a greater degree, changes in soil texture and bioclimate.