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major effect of human-related variables, i.e. tourism planning strategies for the management of biological
and the percentage of agricultural areas. The amount invasions and the conservation of biodiversity in
of tourism can be considered a surrogate for propagule Mediterranean islands.
pressure (McKinney 2002), whereas decreasing agri-
cultural area coverage is an indicator of landscape Acknowledgments We would like to thank the following
regional experts who provided a large amount of data on the non-
transformation, which in turn leads to a reduction in
native flora of the Italian islands for the project ‘‘A survey of the
natural vegetation cover and to the creation of highly non-native flora of Italy’’, funded by the Italian Ministry for the
disturbed sites, both of which promote the establish- Environment, Land and Sea Protection: Pier Virgilio Arrigoni,
ment of non-native plants. Ignazio Camarda, Emanuele Del Guacchio, Gianniantonio
Domina, Pietro Mazzola, Simonetta Peccenini and Lucia Viegi.
Although the joint effect of different sets of
We are most grateful to Bruno Foggi for providing information
explanatory variables were generally of minor impor- and unpublished data on plant invasion in the Tuscan
tance, we did notice a fairly good overlap between Archipelago. We also wish to thank Aldo Marchetto and
geographical and environmental variables, which Francesco Maria Sabatini for their help with the statistical
analysis, as well as Sabina Burrascano, Montserrat Vila ` and two
suggests that these two components act in the same
anonymous reviewers whose valuable comments and suggestions
way on both response matrices. By contrast, the improved this work.
negative interaction between human activity and
environmental variables observed for the established
species seems to indicate that the former counteracts, References
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