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1122 L. Celesti-Grapow et al.

2016; Galasso et al. 2016; Stinca et al. in press). tribution to more islands and those that have pro-
In order to be able to make comparisons, we used gressed to a subsequent stage of the establishment
the same framework for the invasion process as that process within the study area.
adopted in the previous survey. We thus classified the
species as casual (non-native plants that reproduce
spontaneously outside cultivation, but do not form Results
self-replacing populations, and rely on repeated We recorded 203 neophytes. Of these species, 147
introductions for their persistence) or established (72.4%) have become established on at least one is-
(non-native plants that sustain self-replacing popul- land, while the remaining 56 (27.6%) only occur as
ations without direct human intervention), using casuals across the study area. The established spe-
the system standardized on a nationwide scale by cies include 41 (20.2%) reported to be invasive on
the working group for the non-native flora of Italy at least one island. The current list thus contains
(Celesti-Grapow et al. 2009). According to this 49 more species than the previous data-set, which
system, we further classified as invasive any alien listed 154 neophytes, 105 of which were established
established species that have at least one population (68.2%) and 49 casuals (31.8%) (Pretto et al. 2012).
in the study area with individuals that have dispersed, The recorded flora consists of 57 families and 131
survived and reproduced at multiple sites (Blackburn genera. The families and genera represented by the
et al. 2011), i.e. in a strictly biological sense that is highest number of species are shown in Figures 2
based on their rate of spread, regardless of whether the and 3, respectively.
species have a negative environmental and economic The families represented most are Asteraceae (25
impact. Although the term invasive is still used both species), Fabaceae (17 species), Poaceae and Solan-
in the scientific literature and in the applied field aceae (15 species) and Amaranthaceae (12 species),
with different meanings, this approach proved to followed by two families that are represented rela-
be particularly useful for the purposes of our survey tively little in the flora of Italy, i.e. Aizoaceae and
because it makes a distinction between plants that Cactaceae (10 species). Twenty-nine families are
spread more rapidly from those that cause the most represented by only one species. The families with
serious problems, which are two groups that do not the highest number of invasive species are Asteraceae
necessarily overlap, as species that spread fastest are (9), Fabaceae (5) and Cactaceae (4).
not always those that have the worst impacts.
The information derived from the various sources
was integrated into a comprehensive database. The
establishment level of the species in the study area,
defined as casual, naturalized (i.e. established non-in-
vasive) and invasive, was assigned on the basis of the
highest stage in the invasion process documented in
any island. This means that species were considered
as being established if they are so on at least one is-
land. In the present paper, we only deal with those
species that are classified as neophytes on a nation-
wide scale, i.e. plant species introduced in Italy after
the year 1492 (see Celesti-Grapow et al. 2009 for
details on the method). We excluded from the pres-
ent analysis archaeophytes, i.e. ancient introductions,
which remain a controversial group in the Mediter-
ranean region due to the insufficient data to clear-
ly define the origin of several taxa (Celesti-Grapow
et al. 2009; Zohary et al. 2012).
To document the island’s introduced flora and
to outline the major changes that have occurred re-
cently, we analysed the composition of the neophyte
vascular flora of the study area as a whole, and we
compared the current figures with those recorded at
the time of the previous survey, i.e. approximately
in the years 2006–2007 (Celesti-Grapow et al. 2009, Figure 2. The most represented families in the non-native flora
2010b; Pretto et al. 2012). To highlight those taxa of the 37 islands analysed classified according to their level
that are most responsible for recent changes, we of establishment. The numbers next to each bar and those in
brackets refer to the total number of species and the number of
analysed those species that have extended their dis- invasive species in the family, respectively (see text for definitions).