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2568 F. Pretto et al.

the number of both total and established non-native the intentional introductions for horticulture/orna-
species. These findings are consistent with other mental purposes strongly influences propagule pres-
studies conducted on islands (Heatwole and Walker sure, thus raising the likelihood of an invasion event
1989; Kueffer et al. 2010; McMaster 2005). Heatwole (Colautti et al. 2006; Dehnen-Schmutz et al. 2007).
and Walker (1989), for example, stated that tourism Moreover, ornamental plants are often the result of
and human disturbance, associated with the presence human selection processes based on climatic suitabil-
of infrastructures, crops and grazing of domestic ity (Lambdon et al. 2008; Marco et al. 2010), as in the
animals, are the variables that best explain the case of the invasive species belonging to the Carpo-
diversity of non-native plant species in Australian brotus genus, which were introduced from the Cape
coral atolls. With reference to the European continent, region in South Africa and have reached invasive
Pys ˇek et al. (2010b) also stressed the effect of human- status on most of the 37 islands analyzed. Ornamental
mediated factors on climate and, consequently, on taxa add to species introduced in the nineteenth
biological invasion phenomena, as well as the impor- century as fodder or to fence fields, such as Opuntia
tance of considering human variables to understand ficus-indica (L.) Mill. and Agave americana L.
the determinants underlying the number and distribu- Human life on small Italian islands has become
tion of non-native species, regardless of the taxonomy. increasingly reliant on mainland services, particularly
In recent decades, Mediterranean islands have where the development of tourist facilities has dras-
undergone a transition from an economy based largely tically reduced the size of the areas devoted to
on agricultural exploitation to one based on tourist cultivation. As a consequence, the number of total
development (Papayannis and Soroeou 2008). This and established non-native species per island is linked
conversion has had profound consequences on both above all to the ferry crossings and tourist activities,
the social level, with a loss of cultural identity, and on which are more intense on the islands closest to the
the ecosystem level, with changes in land-use. Indeed, mainland. Indeed, the islands that are exploited most
the abandonment of agriculture has led to the recovery by tourists display higher proportions of non-native
of potential natural vegetation in previously cultivated species in their flora. Introduction associated with the
surfaces as well as to the cessation of traditional land accidental transport, i.e. dispersal of seeds through
management techniques, such as terraces, that once clothing and shoes (Pickering et al. 2011), or with the
preserved the slopes that had been damaged by afore-mentioned cultivation of non-native plants
deforestation from soil erosion (Tzanopoulos et al. (ornamentals, forestry, etc.) on these islands may be
2007; Pretto et al. 2010). At the same time, owing to greater than on less frequently visited ones, as the
the increasing demand for tourism facilities, built-up observed differences in the number of successful
areas have often expanded close to existing villages or invasions suggest. The transportation of non-native
along the coast (Tzanopoulos and Vogiatzakis 2011). species by humans overcomes the biogeographical
Our data for the first two islands divided by the barriers that normally hamper the dispersal of animal
regression tree according to tourism pressure, i.e. and plant taxa thus influencing the number of such taxa
Capri and Ischia, confirm that over half of the area on and altering their distribution pattern on islands, as
these two islands is subjected to human activities (52.7 reported by Ficetola and Padoa-Schioppa (2009) for
and 54.6 % respectively). Recent socio-economic reptiles.
changes have also led to a major change in the source The sprawl of artificial surfaces in Mediterraean
of intentional introduction of non-native plant species. small islands results from, among other things, the
Indeed, the role of agriculture in the introduction of construction of hotels, holiday resorts and detached
non-native plant species has progressively decreased, holiday homes or the improvement of existing infra-
while the number of taxa introduced for their aesthetic structures, e.g. road networks. In some cases, artificial
value in gardening activities has grown considerably surfaces have even replaced areas of major nature
(Sanz-Elorza et al. 2009). A large proportion (over conservation interest, particularly along the coasts.
60 %) of the non-native plant species recorded in our Artificial surfaces do not only consist of settlements,
study are likely to have spread in the surrounding areas but of ports and roads designed to provide access to the
after having first been introduced in gardens as more isolated locations, which are often the last refuge
ornamental plants. It is widely acknowledged that for populations of endemic plant species. Settlements

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