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1128 L. Celesti-Grapow et al.

island) or have been recorded for the first time, such they have displayed in recent decades to spread
as A. fourcroydes Lem., which is the latest addition successfully, but above all owing to the detrimental
to the flora, insofar as it was recorded on the island impacts they may have, e.g. the species belonging
of Favignana (34 in Figure 1; Egadi Islands, Sicily), to the genus Carpobrotus, more commonly known
while this paper was being prepared (Galasso et al. as the Hottentot figs. Although the taxonomy of
2016). Carpobrotus in the Italian flora has yet to be clarified,
Although we did not screen species traits systemati- the two main entities belonging to this genus, namely
cally in this study, we did find that succul ence, an C. acinaciformis and C. edulis, and their possible
adaptation of plants to resist drought that is rare hybrids, are considered those that pose, by far,
among native Mediterranean species, is a common the greatest threats to the environment of coastal
trait of the most widespread or emerging taxa in ecosystems in Mediterranean Italy (Camarda et al.
the study area (Tables 1–3), as has been observed 2010; Carranza et al. 2010; Celesti-Grapow et al.
in island and coastal habitats in Italy (Celesti- 2010b; Santoro et al. 2011). Not only are they
Grapow et al. 2010b; Pretto et al. 2010). More among the most frequent (Table 1) and continually
generally, succulence has been found to correlate expanding (Table 2) species in the study area, but
with the invasion success of introduced species in the they are considered a major threat primarily because
Mediterranean Basin (Di Castri 1989; Lloret et al. their spread into natural habitats containing rare and
2005; Lambdon et al. 2008a; Padrón et al. 2011). endemic taxa is seriously threatening the conservation
The possession of functionally novel attributes that of biodiversity on both a local and global scale (Foggi
the native species lack and that make invaders very et al. 2014; Giovino et al. 2015; Lazzaro et al. 2016).
competitive is one of the most commonly advocated Major concerns arise from the fact that these
determinants of the invasion success of introduced plants often naturalize on coastal environments,
species (Wardle et al. 2011). particularly on sea cliffs whose natural habitats
The abundance of succulent species is largely as- have, owing to their inaccessibility, been preserved
cribable to their popularity as ornamentals among even in the presence, ever since the Bronze age, of
the inhabitants of the islands. Succulent plants re- humans that have exploited these islands. Cliffs tend
main attractive throughout the year, can be easily to be very rich in protected habitats and in rare and
propagated and vegetate well even when water and endemic taxa, including vascular plants (e.g. Coppi
space, two resources that are particularly scarce on et al. 2014; Plume et al. 2015; Strumia et al. 2015)
small Mediterranean islands, are limited (Domina & and other remarkable species such as seabirds that
Mazzola 2008). In fact, they grow well in pots and nest in colonies on the rocky coasts of some of these
take up little room in the settlements on the islands. islands. Owing to the difficulties encountered in
Moreover, the popularity of succulents among col- accessing them and the risks of landslides, cliffs are
lectors, who often strive to have as wide a variety as also very challenging sites as regards the planning
possible, increases the size of the species pool. Once of monitoring surveys and eradication or control
they escape from cultivation, their limited need for measures. Several examples of such threats can be
water allows them to survive through the seasonal found on the islands we investigated, such as on
water deficit in the Mediterranean climate and thus Capraia (Figure 1; Tuscan Archipelago), where the
to establish successfully in natural habitats. spread of C. acinaciformis and Senecio angulatus (listed
Crassulaceae and Aizoaceae are, in addition in Tables 1–3) is severely threatening the conservation
to Cactaceae and Agavaceae, further examples of a subpopulation of Centaurea gymnocarpa Moris &
of families with succulent species that are widely De Not., a species that is endemic to the island and
represented in the recorded flora (Figure 2). These is categorized as EN (Endangered) according to the
families include several examples of species that IUCN Red List Criterion (Foggi 2005).
have recently spread to other islands and/or have Several management and nature conservation
progressed in the invasion process (Tables 2 and 3). projects have been undertaken in the Mediterranean
A remarkable example within the family Aizoaceae Basin to tackle these threats posed by vascular plants,
is the ornamental Mesembryanthemum cordifolium, particularly on the European side of the Basin, within
one of the most frequent species on the islands the framework of EU LIFE projects (Brunel et al.
investigated (26 islands, Table 1), which has recently 2013). In this regard, Carpobrotus is the genus that has
become invasive in the study area (Table 3) on, been targeted by the largest number of control and
among other places, the island of Giannutri (8 in eradication actions in the study area. For instance,
Figure 1; Tuscan archipelago), where it has spread the LIFE Project Puffinus Tavolara (LIFE12 NAT/
prevalently on sea cliffs (Lazzaro et al. 2013). IT/000416) is dealing with the local eradication of
Indeed, the Aizoaceae family includes what are Carpobrotus sp.pl. on the island of Tavolara (21 in
undoubtedly the most important plant invaders Figure 1; Sardinia), where this species successfully
in the study area, not only as regards the ability competes with endemic taxa on sand dunes, and in