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Plant invasions on small Mediterranean islands 1129

particular with Linaria sardoa Sommier and Rouya The most widespread taxa also include the
polygama (Desf.) Coincy. Control and eradication Asteraceae family, which proved to be the family
measures targeting Carpobrotus species, often along represented most in the non-native flora of the study
with other species, such as Oxalis pes-caprae and area (Figure 2). Erigeron, which is the most numerous
Casuarina equisetifolia (listed in Table 3) have been, or genus belonging to this family in the analysed flora,
are being, undertaken on the islands belonging to the as well as the genus with the highest number of
Tuscan archipelago, i.e. on Capraia, Elba, Giannutri, invasive species (Figure 3), contains some of the
Pianosa and Montecristo (6 in Figure 1; CoR.E.M. – most widespread non-native synanthropic plants in
CUP E79E1000012000; LIFE project Montecristo urban habitats in Italy (Celesti-Grapow et al. 2001,
2010, LIFE08 NAT/IT/000353; LIFE project 2003, 2013) and in Europe (Lambdon et al. 2008c).
Resto con LIFE, LIFE13 NAT/IT/000471). Some E. bonariensis was found to be one of the species that
of these projects have already yielded encouraging occurred on the highest number of islands (Table 1),
results, i.e. an increase in the number of Centaurea while E. sumatrensis spread to a far higher number
gymnocarpa seedlings has been observed following of islands, even though this remarkable increase
the local eradication of C. acinaciformis on the island (+ 9 islands) (Table 2) may be ascribed to the greater
of Capraia. Invasive plants of the genus Carpobrotus amount of attention dedicated to surveying the
are also among the main targets of the control and human-made habitats in which this species occurs.
eradication measures being implemented on the Our survey highlighted several other examples of
Ponziane islands (9–13 in Figure 1), within the LIFE prominent or emerging taxa, such as Mirabilis jalapa
project PonDerat (LIFE14 NAT/IT/544), which (Table 1), which was reported recently for the first
focuses on the conservation of protected habitats time in the Tuscan Archipelago (Lazzaro et al. 2013)
and endemic flora and seabirds that are currently and which is rapidly spreading on the islands of Elba,
threatened by introduced herbivores, predators and Giglio and Pianosa, Lepidium didymum L., which
invasive plants. was recorded in 2011 in only site in Montecristo
Besides Carpobrotus species, one of the most (Carta et al. 2012) and is now present in several oth-
common targets of these control actions is Ailanthus er sites, and Araujia sericifera Brot., which is natu-
altissima, also known as the tree of heaven, another ralized on Ischia and Capri (15 and 16 in Figure 1)
very frequent species in the study area (Table 1). and is known to cause phytosanitary problems in
This fast growing tree is widespread in human-made agro-ecosystems (Parrella et al. 2013).
habitats on many of the islands we investigated, as
well as in the rest of Europe (Kowarik & Säumel Concluding remarks
2007) and of the country (Badalamenti et al. 2012),
where its growth is considered to seriously threaten A comprehensive analysis of the distribution and
the conservation of ancient monuments and heritage establishment status of all the species is beyond the
sites owing to damage caused by the extensive root scope of this study and will only be possible when
system (Caneva et al. 2003; Celesti-Grapow & Blasi the projects currently under way on some of the
2004; Motti & Stinca 2011); this issue is particularly islands reach a more advanced stage. It will then also
relevant in Italy owing to the vast historical heritage become possible to conduct further analyses to iden-
present in the country. Within the study area, tify the determinants of the patterns recorded, which
A. altissima is also causing problems in natural are probably related to the marked changes that the
habitats. On the island of Panarea (26 in Figure 1, landscape of these islands has undergone, i.e. the
Aeolian Islands, Sicily), for instance, the spread abandonment of traditional land management and
of this tree is severely threatening Silene hiceasiae the concomitant intensification of trade and tourism.
Brullo & Signorello, a species listed as vulnerable Although this overview was not meant to be ex-
by the IUCN that is endemic to the Islands of haustive, it does provide a clear picture, i.e. that there
Panarea and Alicudi (27 in Figure 1, Aeolian Islands, has been a dramatic increase in the number of neo-
Sicily), by forming dense monospecific stands and phyte species, in the extent of their distribution and
invading the perennial grass-covered prairie which in their levels of establishment in recent years. It also
is one of the plant communities to which S. hicesiae indicates that plant invasions on small Mediterrane-
belongs (Domina & Troia 2013). A. altissima has an islands are a serious environmental problem that
been successfully eradicated by means of the Life threatens biodiversity conservation not only in the
project Natura Capraia (LIFE97 NAT/IT/004153) Mediterranean biogeographic region, but also on the
on the island of Capraia, and its eradication is still global scale.
undergoing on the island of Montecristo after the Our results also confirm the general trend reported
positive, though not yet definitive, results of the by various studies in the Mediterranean basin, i.e. in
LIFE project Montecristo 2010 (LIFE08 NAT/ recent times both the number of species introduced
IT/000353). and their levels of invasion have increased dramat-