The vegetation of mining dumps in SW-Sardinia

The vegetation of mining dumps of SW-Sardinia includes several endemic or rare species, that have been confined to such artificial habitats by a millennial mining activity. The extreme edaphic specialisation of these species reflects with unusual fidelity the heterogeneity of substrata, therefore creating a system of plant communities that largely contributes to the environmental diversity of this part of the island. The phytosociological study presented in this paper recognized eight associations, distinguished by the cluster analysis in two main groups, the first including hemicrypto-chamaephytic vegetation, the second including nanophanerophytic garigues. Six associations are belonging to the first group, five of which newly described: Helichryso tyrrhenici-Dianthetum sardoi ass. nov., occurring on gross-grained, hard-sloping dumps deriving from the geologic unit of Gonnesa; Coincyo recurvatae-Helichrysetum tyrrhenici ass. nov., colonizing dumps made of metamorphitic flakes and finer particles; Resedo luteolae-Limonietum merxmuelleri ass. nov., colonizing small-grained mining dumps with high concentrations in sulphides and heavy metals; Ptilostemono casabonae-Iberidetum integerrimae ass. nov., replacing the previous one on older and more consolidated dumps, where the concentration of phytotoxic elements was reduced by the meteoric agents; Epipactidetum tremolsii ass. nov., colonizing muddy deposits originating from ferrous clay; Euphorbio cupanii-Santolinetum insularis Angiolini & Bacchetta 2003, occurring on very old, stabilized dumps. All these associations can be ascribed to the class Scrophulario-Helichrysetea Brullo, Scelsi & Spampinato, 1998. Within this class, a new Sardo-Corsican alliance, Ptilostemono casabonae-Euphorbion cupanii is here proposed, differentiated by a pool of rare or endemic species. In addition to the above- mentioned associations, it is proposed, as well, to include into the new alliance the Polygono scoparii-Helichrysetum tyrrhenici Biondi, Vagge, Fogu & Mossa 1996 corr., that was described for the gravelly riverbeds of Central-Southern Sardinia. As concerns the second group, two new association have been recognized: Dorycnio suffruticosi-Genistetum corsicae ass. nov., found on abandoned, well consolidated mining dumps, with an upper layer altered by pedogenetic processes; Polygalo sardoae-Linetum muelleri ass. nov., occurring in the vicinities of the mines on steep rocky slopes made of Paleozoic metalliferous limestones. Both of them can be ascribed to the alliance Teucrion mari Gamisans & Muracciole 1985, grouping the Sardo-Corsican aspects of Cisto-Lavanduletea Br.-Bl. in Br.-Bl., Molinier & Wagner 1940.