Are some communities of the coastal dune zonation more susceptible to alien plant invasion?

Abstract

Coastal areas, and in particular coastal dunes, are ecosystems
\nstrongly affected by the invasion of alien plants. However, few
\nattempts have ever been made to quantify alien species incidence
\nin different communities along the coastal zonation. This work aims
\nto analyze the distribution of alien plants along the coastal zonation
\nof sandy shores on the Tyrrhenian coast, addressing specifically differences
\namong plant communities in abundance of alien plants.
\nMethods
\nThe study was performed on recent dunes (Holocene) of the central
\nwestern coast of Italy. We selected dune landscapes where invasion
\nprocesses were particularly evident. Vegetation plots were randomly
\nsampled and through cluster analysis, we identified six plant communities
\ncorresponding to the typical zonation described for the
\nTyrrhenian sandy coast of Central Italy.We evaluated and compared
\nfrequency and abundance of invasion in these different communities.
\nFurther, we investigated how propagule pressure (measured using
\nas proxy human structures) contributed to the observed invasion
\npatterns.
\nImportant Findings
\nWe found a relatively low total number of aliens but also a differential
\ndistribution pattern and strong abundance of some of the aliens in
\nspecific sectors of the vegetation zonation. The perennial community
\nof transition dunes appears most affected by invasion processes,
\nrelated almost exclusively to the frequent and widespread Carpobrotus
\naff. acinaciformis. This alien species reaches high cover values,
\napparently lowering cover of native species of transition dune plant
\ncommunities. Higher levels of invasion in the transition dune can be
\npartially explained because of greater propagule pressure in this
\nsection of the dune profile. Our findings thus have important
\nconservation and management implications since transition dune
\ncommunities with Crucianella maritima are rare and protected
\n(sensu Habitat 92/43/EEC Directive) along the entire Italian coast