Effects of the management regime on the performance of the endangered Mediterranean Centaurea horrida Badarò (Asteraceae)

In this study we investigated the effects of the cessation of agro-sylvo-pastoral activities on Centaurea horrida Badaro, a very rare sea-cliff plant, endemic to North-Western Sardinia (Italy) and listed by the IUCN as vulnerable. In a similar way to other cliff species, Centaurea horrida can expand its range when unsuitable surrounding habitats are disturbed. The analysis of aerial photos indicates that about 88.5% of a surface previously occupied by a Centaurea horrida dwarf community was replaced by juniper scrub over a 50-year period. In the juniper scrub Centaurea horrida density is at present 1/5 of that observed in the dwarf community. The spatial distribution of Centaurea horrida individuals was not random but concentrated in open microhabitats, more abundant in the dwarf community than in the juniper scrub. Juveniles were found mainly on bare soil; this being the only microhabitat where seedling emergence may occur. Furthermore, disturbance had a positive effect on the survival rates of saplings. Our data show that Centaurea horrida is a species that is linked to the initial stages of secondary succession, when patches of bare soil are available, but it is non-competitive with the late-succession species of the juniper scrub. Active management practices to maintain Centaurea horrida populations are therefore proposed and discussed. (C) 2008 Elsevier GmbH. All rights reserved