Malcolmia littorea: The isolated Italian population in the European context

Abstract

We compared the coenological information of the only Italian population of Malcolmia littorea (L.) R. Br. with published phytosociological relevés, including ones of this species, throughout its European range. With the aim of highlighting the main climatic features influencing the distribution patterns of M. littorea, we integrated coenological data with some climatic variables and considered major drivers for plant distribution at the European scale. Finally, we analysed the population extent of M. littorea in Italy, in order to assess its conservation status at regional level. The DCA analysis, performed on a matrix 139 relevés × 183 species, separated the relevés according to their floristic composition, showing a geographic gradient from Portugal to Mediterranean coasts, until Italy; with Mediterranean relevés clearly separated from Atlantic ones as well. Along the beach-inland gradient, the analysis highlights that the species is typical of fixed dunes habitats (more inland, mainly stabilised dunes), although in the Atlantic it can also be found in mobile dunes. The analysis of climatic variables in relation to M. littorea distribution, suggested that the species is sensitive to low winter temperature and to summer drought. The only Italian population of M. littorea is subjected to many threats, due to its small dimensions (<1 ha), isolation from the rest of its distribution area, that ranges from Portugal to France (until the Camargue region) and intensive human disturbances. Using both field and remote sensing information, we showed a considerable decrease of the occupied surface in Italy, leading us to suggest that the IUCN threat category of M. littorea in Italy should be reassessed from endangered to critically endangered.

Introduction

Several plant species are characterised by a disjunct distribution in which peripheral populations can be found isolated from the main home range. These have long attracted the attention of many researchers (Abeli et al., 2009, Fjeldså and Lovett, 1997, Gargano et al., 2007, Lutz et al., 2000), interested in understanding historical causes of distribution patterns, ecological and evolutionary relationships across the species range, and models of genetic variations related to isolation and divergence processes (Mosseler et al. 1992). In addition, small and isolated populations are particularly sensitive to different threats (Bucci et al., 1997, IUCN, 2001) and are always at risk of local extinction.

In Italy there are several plant species which show outlying populations isolated from the rest of their range. Examples of these include certain alpine species (Rossi et al. 2009), as well as various plants whose main distributional range is eastern Europe, such as Gentianella crispata (Vis.) Holub (Gargano et al., 2009), and Pinus leucodermis Antoine (Gargano and Bernardo, 2006, Tutin et al., 1993). Malcolmia littorea (L.) R. Br. can be considered as a typical example of a plant characterised by a disjointed distribution. This is a perennial species that forms stable communities in sandy coastal environments and has a W-Mediterranean distribution (Pignatti 1982); it occurs in Portugal, Spain, France, Morocco, Algeria and Italy (Greuter et al., 1986, Tutin et al., 1993), where it is exclusive to the Latium region (Tyrrhenian Central Italy) and at present can be found in a single stand between the small towns of San Felice Circeo and Terracina, far from the rest of its range (Fig. 1). However, the reasons of this distribution are not known.

Although M. littorea appears in several studies related to coastal dune ecology (Dellafiore et al., 2007, Leclerc, 1985), little is still known about its ecology. There is also a scarcity of data concerning the assessment of its conservation status: M. littorea is not included in either the Red List of Spanish vascular flora (Moreno, 2008), or in the Livre Rouge de la flore menacée de France (Olivier et al., 1995), while lists of threatened vascular plants are so far not available for Portugal, Morocco and Algeria. In Italy this species was assigned to different threat categories: Endangered at national level, Extinct in the Wild at regional level in Sicily, and Vulnerable in Latium (Conti et al., 1992, Conti et al., 1997). However, the population extent in Italy is very small (<1 ha) and recently underwent a further decline (Fig. 2; Giovi 2004). In fact, coastal dunes represent threatened ecosystems in most countries and human activities are considered the major disturbance worldwide (Brown and Mclachlan, 2002, Curr et al., 2000). In Europe and particularly in the Mediterranean, human disturbance represents a major threat for coastal ecosystems where this species lives, especially because of urban expansion and tourist development (Carboni et al., 2010, Defeo et al., 2009).

In light of these considerations, it is important to re-assess the conservation status of Malcolmia littorea in Italy, and to investigate its ecological requirements in order to protect it successfully. Specifically, in this paper we compared the coenological information recorded in the only M. littorea Italian population with different phytosociological relevés including those of the same species in other European countries. Then, with the aim of identifying the main climatic features influencing the distribution patterns of this species, we integrated in the analyses climatic variables which are considered major drivers of plant distributions at the European scale (Thuiller et al., 2004, Zimmermann et al., 2009). Finally, we analysed the population extent of M. littorea in Italy, in order to assess its conservation status at a regional level.