Folia Geobot (2016) 51:129–141 DOI 10.1007/s12224-016-9249-9 Quantifying plant species diversity in coastal dunes: a piece of help from spatially constrained rarefaction Daniela Ciccarelli & Giovanni Bacaro Received: 2 July 2015 /Accepted: 12 May 2016 /Published online: 13 August 2016 # Institute of Botany, Academy of Sciences of the Czech Republic 2016 Abstract Since coastal dunes are one of the most vul- gradient with the highest values at the level of mobile nerable landscapes in Europe, their maintenance re- dunes and transition dunes. Species richness was signif- quires specific conservation and monitoring icantly higher in stable coastal dunes than those found in programmes. In this paper, the coastal dune systems of accreting and in erosive dunes. In fact, sand dynamics two natural parks located in central Italy were analyzed (accumulation as well as erosion) create periodic vege- aiming at: (1) assessing diversity patterns of all vascular tation disturbances affecting composition variability and species, endemic and alien taxa in plant communities succession. The SCR methodology avoided overestima- along the coast-to-inland gradient; (2) comparing these tion of species richness when compared to classical patterns between coastal sections characterized by dif- rarefaction curves. Our findings pinpointed that coastal ferent dynamical processes (accreting, stable and ero- plant communities create a highly spatially structured sive coasts); and (3) testing the differences induced by mosaic in which mobile dunes represent the highest the methodological approach used to characterize these compositional heterogeneity. Local managers are en- patterns. Twenty-one transects were randomly posi- couraged to consider these results for planning adequate tioned perpendicular to the shoreline in the whole coast- conservation strategies. al area (30 km in length), and the full spectrum of plant communities was sampled. Patterns of plant diversity Keywords biodiversity. coastline dynamic processes . were assessed using spatially explicit methods, namely coastal dune vegetation . Natura 2000 . rarefaction spatial constrained rarefaction (SCR), able to avoid the curves . spatial autocorrelation confounding effect of spatial autocorrelation. The re- sults show that species richness varied significantly Abbreviations between plant communities along the coast-to-inland SCR spatially constrained rarefaction MSRM Migliarino San Rossore Massaciuccoli Regional Park Nomenclature Checklist of the Italian vascular flora (Conti et al. MP Maremma Regional Park 2005, 2007) for plant species. D. Ciccarelli (*) Department of Biology, University of Pisa, Via Luca Ghini 13, 56126 Pisa, Italy Introduction e-mail: [email protected] ‘ ’ G. Bacaro The term biodiversity is currently used in the literature Department of Life Sciences, University of Trieste, Via L. Girgieri to cover both the number of different populations and 10, 34127 Trieste, Italy species that exist and the complex interactions that occur 130 D. Ciccarelli, G. Bacaro among them. Its measurement at all levels is really Chiarucci et al. 2012). Even if this method offers an important for any conservation biology purposes elegant solution to the interpolation of the number of (Pullin 2002). The effects of biodiversity loss or changes species observed as a function of sample size, it is in plant community composition on the functioning of affected by various spatial components. However, after ecosystems have been the focus of much ecological Chiarucci et al. (2009) and Bacaro et al. (2012a), the research (Schulze and Mooney 1993; Kinzig et al. problem related to the lack of independence in the 2002; Loreau et al. 2002). Species composition, rich- sampling units between samples has been considered ness, evenness and interactions all respond to and influ- thanks to spatially constrained rarefaction (SCR) that ence ecosystem properties and stability. Unfortunately, incorporates the autocorrelated structure of biological the ever-growing impact of human activities is causing communities into sample-based rarefaction. More spe- biodiversity loss of natural habitats (Hawksworth and cifically, this method addressed the problem of spatial Bull 2008). autocorrelation by building the rarefaction curve based Coastal sand dune systems are dynamic and hetero- on the adjacency of the sampling units. Nevertheless, geneous habitats characterized by a complex environ- the use of SCRs has not yet become routine (the only mental gradient which determines a characteristic coast- recent ecological application can be found in Janišová to-inland plant community zonation (Ranwell 1972; et al. (2014) and is expected to be particularly useful in Doing 1985;Psuty2004; Wiedemann and Pickart those situations where the spatial structure of biological 2004; Frederiksen et al. 2006;Acostaetal.2007). communities is high, as is the case in coastal dune They contain a high ecological diversity in terms of systems. plant community composition, species rarity and ende- Erosion has a serious impact on some 20 % of the mism (van der Maarel and van der Maarel-Versluys coastline of Europe (Doody 2013). In Italy, 42 % of 1996; van der Maarel 2003; Martínez et al. 2004; coasts are largely affected by erosion processes, and in Ciccarelli et al. 2014). Unfortunately, coastal dune en- particular the Tuscan coastline reflects this scenario, vironments are one of the most vulnerable landscapes in with 37 % of its sand dune systems being affected by Europe, prone to many stress and disturbance factors erosion (Gruppo Nazionale per la Ricerca such as erosion, global warming and anthropogenic sull’Ambiente Costiero 2006). Although it has been pressure (Cori 1999; Brown and McLachlan 2002;van assessed that shoreline erosional processes are one of der Maarel 2003; Coombes et al. 2008; Carboni et al. the major threats for coastal sand dune systems world- 2009; Gornish and Miller 2010; Miller et al. 2010; wide, little is known regarding plant diversity and coast- Ciccarelli et al. 2012; Ciccarelli 2014, 2015). line erosion (Roman and Nordstrom 1988; Avis and Quantifying the number of species that occur along a Lubke 1996; García-Mora et al. 1999; Lubke and coast-to-inland ecological gradient could make a valu- Hertling 2001; da Silva et al. 2008; Ciccarelli et al. able contribution to managing the ecosystem. 2012;Ciccarelli2014). It should be considered that the examination of spe- In this paper, a systematic sampling design based on cies distribution patterns in space can help us better belt transects was used to sample the full spectrum of understand the effects of ecological and environmental coastal dune plant communities. Considering that bio- pressures. To quantify the relative importance of natural diversity loss is a critical issue in coastal environments, and anthropogenic pressures at appropriate spatial we analyzed the diversity patterns of vascular plant scales, both spatial and spatial-temporal analyses are species across the coastal dune systems of two natural required. The species’ spatial distribution and their rela- parks in Tuscany (Italy) in order to correctly characterize tionship with the environmental heterogeneity should be occurring diversity patterns. In detail, we specifically explored using specifically developed techniques. aimed at (1) assessing diversity patterns of all vascular Among these, individual and sample-based rarefaction species, endemic and alien taxa in plant community curves are widely recognized powerful tools, also used types along the coast-to-inland gradient; (2) comparing to evaluate the effectiveness of sampling and to compare these patterns between coastal sections characterized by species richness in different habitats (Gotelli and different dynamical processes (accreting, stable and ero- Colwell 2001; Moreno and Halffter 2001; Koellner sive coasts); and, finally, (3) testing the influence of the et al. 2004; Crist and Veech 2006; Chiarucci et al. methodological approaches used (e.g. regular rarefac- 2008a,b;Acostaetal.2009; Bacaro et al. 2012a; tion vs spatially constrained rarefaction) for diversity Quantifying plant species diversity in coastal dunes 131 comparisons purposes. This latter point has major im- The Maremma Regional Park is located on the plications when conservation actions should be planned coast near Grosseto, in the southern part of Tuscany. and, for this reason, deserves particular attention. The Park is 90 km2 and offers a diverse array of landscape types: coastal dunes, inland salt marshes, rocky vegetated foothills, coastal pinewood and Material and methods farming areas. This area is characterized by a C1 type of climate, Mediterranean sub-arid, with an Study area average annual temperature of 15.6°C and an aver- age annual rainfall of 618 mm (Pinna 1985). The present study was conducted in the coastal sand The coastal dune systems of both parks belong to dunes of two protected areas along the Tuscan littoral the Natura 2000 network and include the following (Italy): Migliarino-San Rossore-Massaciuccoli Regional Sites of Community Importance (SCIs): ‘Coastal sand Park (MSRM) and Maremma Regional Park (MP; Fig. 1). dunes of Torre del Lago’ and ‘Coastal sand dunes of The Migliarino-San Rossore-Massaciuccoli Uccellina’, respectively. Moreover, these two protected Regional Park covers an area of 142 km2 and is located areas are a geomorphological reference system for near Pisa, in the North of Tuscany. The Park hosts investigating variability of species richness