Bio-ecological, phytosociological and conservation aspects of relictual and disjointed populations of Simethis mattiazzi (Vandelli) Sacc. (Xanthorrhoeaceae) in the Channel of Sicily

摘要

Two populations of Simethis mattiazzi (Xanthorrhoeaceae) were recently discovered in the Channel of Sicily - (1) Punta Bassana (Marettimo Island) and (2) Mount S. Giuliano (western Sicily) - at a considerable distance from the nearest stations hitherto known, located in southern Sardinia, the Pontine Islands Archipelago and Tunisia. The taxonomical and distributive aspects of this species are analysed to highlight the relictual and biogeographical significance of the disjointed and fragmentary nuclei distributed in several small islands of the Channel of Sicily, the Italian Peninsula and North Africa. Some morphological, biological, ecological and phytosociological aspects of the two new populations are analysed to assess risk factors. These relictual populations are included in a residual garrigue ascribed to the association Erico - Micromerietum fruticulosae, endemic to western Sicily and characterized by a significant frequency of endemic or rare species. The coenose is tied to the calcareous dolomite rocky ridges located near the coast and exposed to humid currents from the sea; this ecological combination gives to the habitat a character of oceanic environmental conditions, somewhat similar to the Atlantic stations where the main range of the species gravitates. The survey has shown the populations to be formed of a small number of individuals at both stations, which has further highlighted the biological precariousness of these populations, located at the extreme south-eastern limit of the range of the species. The threats of anthropogenic nature, such as reforestation with non-native conifers, but mostly by fires, the frequency of which tends to alter the integrity of the sites, increase this vulnerability. The IUCN "risk status" for the regional territory of Sicily of S. mattiazzi is to be ascribed to the "Critically endangered" category, in accordance with the B1ab (ii) and B2ab (ii) criteria of the IUCN. The same "risk status" is likely to be extended to the other isolated stations of the western Mediterranean.