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Plant invasions on small Mediterranean islands 1125

Table 3. List of the non-native vascular plant species that have progressed to a subsequent stage of the invasion process within the study
area as regards the previous survey (Pretto et al. 2012).
Taxon Family Est Prev est
Acacia dealbata Link Fabaceae I C
Acacia melanoxylon R.Br. Fabaceae N C
Acacia pycnantha Benth. Fabaceae I C
Aeonium haworthii Salm-Dyck ex Webb & Berth. Crassulaceae N C
Anredera cordifolia (Ten.) Steenis Basellaceae I C
Campsis radicans (L.) Bureau Bignoniaceae N C
Casuarina equisetifolia L. Casuarinaceae N C
Delairea odorata Lem. Asteraceae N C
Drosanthemum floribundum (Haw.) Schwantes Aizoaceae N C
Dysphania ambrosioides (L.) Mosyakin & Clemants Amaranthaceae I N
Erigeron karvinskianus DC. Asteraceae I N
Eucalyptus globulus Labill. Myrtaceae N C
Euphorbia maculata L. Euphorbiaceae I N
Lonicera japonica Thunb. Caprifoliaceae N C
Mesembryanthemum cordifolium L.f. Aizoaceae I N
Mirabilis jalapa L. Nyctaginaceae I N
Opuntia stricta (Haw.) Haw. Cactaceae I C
Paraserianthes lophantha (Willd.) I. C.Nielsen Fabaceae I N
Passiflora caerulea L. Passifloraceae N C
Phytolacca americana L. Phytolaccaceae I N
Prunus domestica L. Rosaceae N C
Senecio angulatus L.f. Asteraceae I N
Tradescantia fluminensis Vell. Commelinaceae N C
Zantedeschia aethiopica (L.) Spreng. Araceae I N
Notes: Est = current establishment status in the study area, assigned on the basis of the highest stage in the invasion process documented
in any island. Prev est = establishment status in the study area in the previous survey (see text for details on the methods).

species occur, only recently being considered in new taxa to the island’s spontaneous flora. Indeed,
floristic studies. In fact, the detection of those taxa a dramatic rise in the number of non-native species
that are still in an early phase of invasion has become and in establishment events on Italian islands has
an important issue in both the research on and been reported by several sources in recent years (e.g.
management of invasive species only in these last Domina et al. 2012; Pasta et al. 2012; Podda et al.
years, especially following the regulation adopted by 2012; Stinca & Motti 2013; Lazzaro et al. 2014a;
the European Union on invasive alien species (EU Del Guacchio 2015; Camarda et al. 2016), with
2014), because some may spread and have serious new species being detected even on islands whose
ecological and economic impacts in the future (see introduced flora was already well known and has been
for example Brundu et al. 2013, 2015). continually monitored in recent decades, such as
Although this greater attention has led to the Capraia and Elba in Tuscany (Foggi et al. 2001, 2006;
recording of new casual species, the percentage of Lastrucci et al. 2012; Ferretti et al. 2013; Lazzaro
this non-established component within the overall et al. 2013, 2016), Capri and Ischia in Campania
flora in the study area (27.6%) has actually decreased (Ricciardi 1998; Ricciardi & Mazzoleni 2011; Stinca
since the previous survey (31.8%) because several & Motti 2013; Stinca et al. 2013, in press), the Pelagie
taxa have in the meantime established (Table 3). archipelago in Sicily (Brullo & Siracusa 1996; Pasta
Moreover, this percentage appears to be relatively 2001; Domina & Mazzola 2008; Domina et al. 2012)
low if compared with those in other study areas in and many of the small islands that surround Sardinia
Italy. For instance, casuals account for 42.7% of (Bocchieri 1992; Camarda et al. 2016).
the non-native flora in the whole country (Celesti- A recent sharp increase in the number of alien
Grapow et al. 2009), and for as much as 64.5% in species is a generalized phenomenon in Europe and
the metropolitan area of Rome (Celesti-Grapow the Mediterranean Basin that has significant conse-
et al. 2013). This relatively low presence of casual quences on biodiversity (Hulme et al. 2009; Butchart
species in the flora of the study area may in part et al. 2010). The majority of these new additions to
be attributed to the absence of large urban areas, the islands’ flora have probably long been present on
which are acknowledged as major centres for the the investigated islands as cultivated plants and may
introduction of non-native plants (Ricotta et al. only recently have escaped and started to reproduce
2012; Capotorti et al. 2013). spontaneously. Other species may have derived from
However, the intensification in research and new introductions, whether deliberate or accidental,
greater focus on aliens only partially explain the from the mainland or from the major islands Sic-
increase recorded in the number of species, which ily and Sardinia. Although the lack of information
has also been shown to result from the addition of on the history of the introduction of the various