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Biol Invasions (2012) 14:2559–2572
DOI 10.1007/s10530-012-0252-7
ORIGINAL PAPER

Determinants of non-native plant species richness
and composition across small Mediterranean islands

F. Pretto • L. Celesti-Grapow • E. Carli •
G. Brundu • C. Blasi

Received: 4 October 2011 / Accepted: 16 May 2012 / Published online: 29 May 2012
Ó Springer Science+Business Media B.V. 2012

Abstract The main aim of this paper is to assess the development of tourist facilities. Our results indicate
drivers of non-native plant species richness and that tourism and the increase in the extension of
composition on a set of 37 small Mediterranean artificial surfaces are also the main drivers of non-
islands in Italy. We compiled the list of the non-native native plant species occurrence and establishment.
flora and distinguished species according to their These factors outweigh the effects of abiotic variables
establishment status. The non-native flora of the such as climate and lithology in determining the
islands studied consists of 154 species, 105 of which number of non-native species, whether it be total or
are established on at least one island. Regression tree established, as well as variations in the composition of
analysis revealed that the main determinants of both established species. High human pressure and orna-
total non-native and established non-native species mental introductions associated with tourist activities
richness are the variables linked to tourist develop- appear to be the key elements that need to be
ment and the sprawl of artificial surfaces. The considered when planning strategies aimed at manag-
variation partitioning approach shows that the varia- ing plant invasions in Mediterranean islands.
tion in total non-native flora composition is driven
above all by environmental variables, whereas when Keywords Introduced flora Italy Plant invasions
established taxa are considered, human-mediated Regression tree Tourism Variation partitioning
factors account for most of the explained variation.
Mediterranean islands have recently experienced
changes in the type and intensity of human activities,
leading to a decline in rural landscape and the Introduction

Islands have often been considered as ‘‘natural labo-
F. Pretto L. Celesti-Grapow (&) E. Carli C. Blasi
Environmental Biology Department, Sapienza University ratories’’ for studies on the genetics, demography and
of Rome, Rome, Italy ecology of biological communities (Whittaker and
e-mail: laura.celesti@uniroma1.it
Ferna ´ndez-Palacios 2008). Islands also provide excel-
lent study systems to assess the impact of invasive
E. Carli
S.T.A.T. Department, University of Molise, non-native species and to test specific hypotheses
Campobasso, Italy concerning biological invasions (Affre et al. 2010;
Kueffer et al. 2010). Nevertheless, the issue of the
G. Brundu
Science for Nature and Environmental Resources susceptibility of islands to biological invasion, which
Department, University of Sassari, Sassari, Italy has always been regarded as one of the most classic

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