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Islands and plants: preservation and understanding of flora on Mediterranean islands

Alien introduction
The data reported in Table 5 suggest that volcanic islands are more vulnerable
than other kinds of islands to xenophytes. The data also confirm a pattern
previously observed on many other Mediterranean and Canarian islands,
which is that the vulnerability to alien invasion is positively correlated with the
endemism rate. Many xenophytes are already established on the circum-Sicilian
islands. They were mostly introduced for ornamental purposes (Mazzola &
Domina, 2008) and began to become naturalised during the 19th century (Pasta,
2003). Some currently act as dangerous invaders and are menacing not only to
pre-forest and forest communities (e.g., Acacia spp., Ailanthus altissima, and
Paraserianthes lophantha: Villari & Zaccone, 1999; Badalamenti et al., 2012;
Pasta et al., 2012b) and coastal communities (e.g. Carpobrotus spp., Pennisetum
setaceum: Vilà et al., 2006; Pasta et al., 2010), but also to islet endemics (Troìa
et al., 2005; Pasta & La Mantia, 2008). Global warming may have played an
important role in the steep increase of casual, naturalized, and even invasive
aliens on Sicilian satellite islands during recent decades, and the ecological
consequences of this trend could be even more severe in the future (Gritti et
al., 2006; Heywood, 2011).

Table 5. A rough comparison between the conservation value and the invasion rate of the
vascular flora of 18 circum-Sicilian islets. Island abbreviations are provided in Table 3.

Afforestation
Since the 1960s, some parts of Lampedusa, Linosa, Marettimo, Levanzo,
Ustica, Salina, Vulcano and Favignana have been used for the development of
artificial plantations. Unfortunately, these plantations have greatly reduced local
plant diversity and harmed ecosystem functioning, especially in plantations
where the final canopy cover is too dense, where needle litter is not managed,
and where soil erosion is excessive because of incorrect pre-planting practices
(Pasta et al., 2012a). In particular, the use of non-native Pinus halepensis
germplasm has substantially reduced the survival of the small remnant nuclei of

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