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Plant invasions on small Mediterranean islands 1121

substratum varies considerably (i.e. volcanic, sedi-
mentary, metamorphic) and many of them display
marked topographic variations, with mountains, the
highest of which is found on the Island of Elba and
rises to 1,050 metres, and prevalently rocky shores.
They all belong to the Mediterranean climatic region
(Blasi et al. 2014), although there are some varia-
tions between the islands in temperature and annual
rainfall along the north–south gradient, as their lati-
tude ranges from 35° 29′ N to 44° 2′ N.
All the islands investigated have been subjected,
albeit to varying degrees of intensity, to the impact of
man since ancient times, mainly in the forms of forest
exploitation, wildfires, introduction of domestic
herbivores, agriculture and, more recently, tourism,
with the consequent expansion of settlements,
infrastructures and communication routes. Most
are currently permanently inhabited, though some
have been used exclusively as prisons, military areas
or nature reserves, thereby limiting human access.
Eight of these islands, i.e. Palmaria which lies off
the Cinque Terre coast, and Alicudi, Filicudi, Lipari,
Panarea, Salina, Stromboli and Vulcano in the
Aeolian archipelago to the north of Sicily (Figure
1), are included in the UNESCO World Heritage
sites on account of their landscape and natural
Figure 1. Location of the 37 islands analysed. 1 Palmaria; Liguria. peculiarities (WHC 2016). Further details on the
2 Gorgona, 3 Capraia, 4 Elba, 5 Pianosa, 6 Montecristo, 7 Giglio,
8 Giannutri; Tuscany. 9 Zannone, 10 Palmarola, 11 Ponza, islands’ characteristics can be found in Ricciardi
12 Ventotene, 13 Santo Stefano; Lazio. 14 Procida, 15 Ischia, (1998), Ricciardi et al. (2004), Domina and Mazzola
16 Capri; Campania. 17 La Maddalena, 18 Caprera, 19 Asinara, (2008, 2011), Pretto et al. (2010, 2012), and Lazzaro
20 Isola Piana, 21 Tavolara, 22 Molara, 23 San Pietro; Sardinia.
24 Ustica, 25 Stromboli, 26 Panarea, 27 Alicudi, 28 Filicudi, et al. (2014a, 2016).
29 Salina, 30 Lipari, 31 Vulcano, 32 Marettimo, 33 Levanzo, The information on the non-native vascular flora
34 Favignana, 35 Pantelleria, 36 Linosa, 37 Lampedusa; Sicily.
was compiled by a team of botanists from each of
the 6 Italian administrative regions to which the 37
islands belong (Liguria, Tuscany, Lazio, Campania,
Study area and methods
Sardinia and Sicily; Figure 1), following a consoli-
We analysed the same islands as those selected by dated tradition in Italy of compiling floristic inven-
Pretto et al. (2012) so as to be able to detect the most tories by integrating data collected by local research
recent changes in their introduced flora. The study groups at the regional scale. The network largely in-
area therefore included 37 small islands located volved the same researchers as those who provided
in the middle of the Mediterranean sea, off the data on the flora of these islands during the previous
Tyrrhenian Coast of Italy and around Sicily and survey (Celesti-Grapow et al. 2010b; Pretto et al.
Sardinia (Figure 1). As small islands were defined as 2012). To allow the data collected during this survey
islands whose area covers less than 10,000 km and to be compared with those from the previous survey,
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that have a population of less than 500,000 inhab- we used the taxonomy scheme adopted in the lat-
itants, Sicily and Sardinia were excluded from the est general inventory of the non-native flora of Italy
data-set of Pretto et al. (2012) on account of both (Celesti-Grapow et al. 2009), although in some cases
their size (25,707 km and 24,090 km , respectively) applying the most recent nomenclature (Euro+ Med
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and population (5,074,261 and 1,658,138, respec- 2006).
tively) (ISTAT 2016). Several other islands were The information on the distribution and the
also excluded from the data-set for specific reasons. establishment status of each species on every island
Sant’Antioco, for instance, the fourth largest island was updated and re-assessed using the recently
in Italy after Sicily, Sardinia and Elba, was excluded published literature and new field surveys (Arrigoni
because it is connected to Sardinia by a bridge. The & Viegi 2011; Domina et al. 2012; Stinca & Motti
size of the 37 islands varies from 0.31 to 224.20 km 2013; Stinca et al. 2013, 2016; Ardenghi et al.
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and their resident population varies from 0 to 56,105 2014; Lazzaro et al. 2014a; Del Guacchio 2015;
inhabitants (Pretto et al. 2012). Their lithological Del Guacchio & Vallariello 2015; Camarda et al.