La flore vasculaire de l’île de Cavallo (archipel des Lavezzi, Corse) : diversité, intérêt biogéographique et conservation

Abstract

This study provides the first detailed assessment of the vascular flora of the Cavallo Island and its three satellite islands or islets (Corsica, Bouchesde-Bonifacio). It is the Corsican island which has the highest floristic richness with 440 taxa (species and subspecies), all inventories combined. The current flora (i. e. occurring after 1990) includes 426 taxa, of which 371 indigenous and 55 exotic plants, introduced voluntarily or not by man. Of this total, 155 taxa (109 indigenous and 46 exotics) were never been reported on the Lavezzi archipelago. This high floristic richness, compared to other west-Mediterranean islands of similar size, is explained by the area of Cavallo island, the largest of the peri-corsican islands, and to the diversity of environments, including the presence of a permanent lake, the Greco lake. Cavallo Island and its islets contain 70 plant species of importance (i. e. endemic, rare, protected or threatened), eight of which were not currently inventoried. These surveys performed in 2013–2015 highlight the presence of some very rare plants in Corsica (Anacamptis morio subsp. longicornu, Callitriche brutia, Limonium bonifaciense, Limonium strictissimum) and infrequent endemics (Acis rosea, Bryonia marmorata, Crocus minimus, Serapias nurrica, Silene velutina) that were not known to the island. The strong human impact explains the presence of 55 introduced taxa and at least subspontaneous in the «natural environment», of which 50 had not yet been reported on the island. The results of this study are discussed in terms of (1) specific richness compared to other western Mediterranean islands of similar surface, (2) functional diversity (analysis of demographic strategies of Grime), (3) biogeographic originality and conservation issues in order to better preserve in the future this exceptional floristic heritage but for too long unrecognized.