Abstract
We conducted a phytosociological study of the halophile, chamaephytic, and hemicryptophytic communities found on coastal sand dunes and salt marshes in Tuscany, which mainly consist of Limonium spp. We describe the presence in Tuscany of communities referred to as Mediterranean salt steppes (Limonietalia), although we emphasize that they cover only small areas. We describe a new association, Limbardo crithmoidis-Limonietum etrusci, and a new alliance endemic to Tuscany, Limonion etrusci.
Résumé
L’article présente l’analyse phytosociologique des communauté halophiles chamaephytiques et hémicryptophytiques dominées par Limonium sp. pl., qui se trouvent sur les revers dunaires et le bord des étangs saumâtres des côtes toscanes. Il est mis en évidence la présence de communautés imputables à l’ordre Limonietalia qui couvrent de petites surfaces; et décrit une nouvelle association (Limbardo crithmoidis-Limonietum etrusci) et une nouvelle alliance (Limonion etrusci) endémiques de la Toscane.
Introduction
The genus Limonium (Plumbaginaceae) includes thirteen species in Tuscany, twelve of which are endemic (Conti et al., Citation2005). All species are perennial, chamaephytic or hemicryptophytic, halophilic or halotolerant plants. Ten species are diploid micro-species belonging to the group L. multiforme (Rizzotto, Citation1984, Citation1999), which is distributed along Tuscan rocky coasts from Livorno (Leghorn) to the Argentario promontory, and on several Tuscan archipelago islands, except Capraia, where a triploid species with a typical Corsica-Sardinia distribution is present, L. contortirameum (L. caprarium Rizzotto according to Rizzotto, Citation1999). All species inhabit cliffs and rocky shore habitats referred to as the Crithmo-Staticetea class (Arrigoni & Di Tommaso, Citation1981; Foggi & Grigioni, Citation1999; Foggi et al., Citation2006; Viciani et al., Citation2007; Foggi & Pancioli, Citation2008; Foggi et al., Citation2008a). Two other Limonium species grow in Tuscany, L. narbonense and L. etruscum, which inhabit coastal dune habitats, salt/sand/silt substrata, and salt steppes or meadows, referred to as the order Limonietalia by previous authors, but more widely known as Mediterranean salt steppes (Rivas-Martínez et al., Citation2002; Biondi & Blasi, Citation2009). In Tuscany, these communities only occupy small areas, which are not comparable to those found in other regions of southern Italy (e.g. Sicily, see Brullo & Furnari, Citation1976; Sardinia, see Biondi et al., Citation2001a, b; Molise, see Stanisci et al., Citation2007) and possibly those in northern regions (Poldini et al., Citation2006; Bassi, Citation2007; Cazzin et al., Citation2009). However, they are of considerable conservation interest, because of the presence of L. etruscum, which is a strictly endemic species (Arrigoni & Rizzotto, Citation1985; Foggi et al., Citation2008b; Viciani et al., Citation2011). Mediterranean salt steppes, an important European Community habitat (Limonietalia, Natura 2000 code 1510), were originally not clearly defined in the ‘Interpretation Manual of European Union Habitats’ (see Farris et al., Citation2007; Argagnon, Citation2008). The latest edition of the ‘Italian Interpretation Manual of Directive 92/43/CEE Habitats’ (Biondi & Blasi, Citation2009) reports that this habitat is probably present in Tuscany, which led us to undertake literature and field investigations with the aim of identifying the presence of phytocoenoses meeting this habitat definition and describing them from a phytosociological perspective.
Material and Methods
The syntaxonomical literature does not report any communities in Tuscany that are attributed to the order Limonietalia (Mediterranean salt steppes), so we reconsidered all published phytosociological surveys where L. narbonense or L. etruscum were dominant or subdominant species, in order to determine whether they could be referred to as Limonietalia from a coenological point of view. No vegetation data were found relating to L. etruscum in phytocoenoses characteristic of this species, so we carried out 14 surveys using the Braun-Blanquet (Citation1932, Citation1951) method. In contrast, we found six surveys from the literature where L. narbonense was a dominant species (Arrigoni et al., Citation1985; Viciani & Lombardi, Citation2001; Viciani et al., Citation2001; Andreucci, Citation2004; Sani & Tomei, Citation2006). We assembled a comprehensive table containing all published and unpublished surveys describing L. etruscum and L. narbonense. The locations of the surveys are shown in Fig. .
Fig. 1 Locations of the surveys. Fig. 1 Localités des relevés.
We performed exploratory analyses of the comprehensive table using standard statistical methods. We performed a cluster analysis (hierarchical classification) on a matrix design of species × surveys, after transforming it to an ordinal scale according to the method of Van Der Maarel (Citation1979) and Noest et al. (Citation1989). We used average linkage (UPGMA) and Euclidean distance measures in the program Syntax V (Podani, Citation2002). Multidimensional scaling (NMDS) and principal component analyses (PCA) were performed with SPSS (Citation2003), using the matrix of normalized Euclidean distances.
Citations of syntaxa and floristic species names are provided without authors. Complete syntaxa names are reported in the syntaxonomic scheme with a list of other syntaxa quoted. We followed Rivas-Martínez et al. (Citation2002) for syntaxonomic nomenclature, whereas the nomenclature of floristic species is given according to Conti et al. (Citation2005, Citation2007), Kerguélen (Citation1999), Pignatti (Citation1982) and Tutin et al. (Citation1964-Citation1980, 1993).
Results and discussion
As expected, the dendrogram obtained by cluster analysis (Fig. ) clearly separated surveys featuring L. etruscum (rel. no. 1-14) from those featuring L. narbonense (rel. no. 15–20), which indicates two floristically well-distinguished communities. We identified a secondary subdivision in the L. etruscum group, which first splits at rel. 14 and then separates into two groups (rel. 1-8 and 9-13). The first division separates at rel. 20 in the L. narbonense group.
Fig. 2 Dendrogram of surveys obtained using cluster analysis. Fig. 2 Dendrogramme des relevés obtenu par regroupements hiérarchiques.
The PCA spread the surveys along the x-axis and the two groups characterized by the two Limonium species were placed at opposite extremes. NMDS (Fig. ) confirmed these two principal groups and placed them to the left (L. etruscum group) and right (L. narbonense group) of the y-axis. The two L. etruscum surveys subgroups separated on the x-axis corresponded to the two different locations (Livorno and Grosseto) for this species.
Fig. 3 NMDS of Tuscan Limonietalia surveys. Fig. 3 NMDS des relevés Toscans imputables à l’ordre Limonietalia.
Our statistical analysis provided good support for our interpretation of Limonium community structures, which we describe as follows.
Limonium narbonense communities
In the past, the few reports of L. narbonense coenoses found in the phytosociological literature of Tuscany were assembled in tables together with surveys dominated by other species in different types of associations referred to as Mediterranean salt marshes and salt pans (Sarcocornietalia fruticosae) or Mediterranean salt meadows (Juncetalia maritimi) (see Arrigoni et al., Citation1985; Viciani & Lombardi, Citation2001; Viciani et al., Citation2001; Andreucci, Citation2004; Sani & Tomei, Citation2006). When these surveys are grouped into a single table (Table ), we discover that a community dominated by L. narbonense is sporadically distributed in the coastal salt marshes and meadows of Southern Tuscany, from the Follonica Gulf to the Orbetello Lagoon. These phytocoenoses are mainly found on the margins of salt marshes on clay-silt soils, which are periodically inundated in winter, but subject to summer drying. These regions are in contact with Sarcocornia scrubby formations (Sarcocornietum deflexae) and form a transition zone with more arid coenoses dominated by Atriplex portulacoides or Puccinellia festuciformis, or with more humid and less salty coenoses belonging to the Mediterranean salt meadows (Juncetalia maritimi). Limonium. narbonense communities are found to cover small regions in protected areas, but these are floristically poor and residual probably because of human disturbance and the consequent scarcity of suitable environments. For these reasons, it is not possible to define an association from a syntaxonomic view point. The first five surveys in Table can be attributed to the Limonietalia order, because of the dominant species and the clear prevalence of Sarcocornietea fruticosae plants in respect with Juncetea maritimi species. However, the sixth survey (no. 20, San Rossore) can be interpreted as a transition zone between Mediterranean salt steppe coenoses (Limonietalia) and Mediterranean salt meadow coenoses (Juncetalia maritimi).
Table 1. Limonium narbonense communities. rel. 15-19: Limonium narbonense conenoses rel. 20: Aspects of transitions between Limonietalia and Juncetea / Juncetalia maritimi. Tableau I Communauté à Limonium narbonense. rel. 15-19: Limonium narbonense cénoses. rel. 20: Aspect de transition entre Limonietalia et Juncetea/Juncetalia maritimi.
Limonium etruscum communities
Limonium etruscum is a rare species that is strictly endemic to Tuscany, which was first described on sandy coasts of Maremma (Arrigoni & Rizzotto, Citation1985). According to Arrigoni & Rizzotto (Citation1985), L. etruscum is morphologically similar to L. glomeratum, L. densiflorum, and L. selinuntinum, distributed in Sardinia and/or Sicily, where they inhabit coastal areas temporarily permeated by salty water. L. etruscum is known from two populations, one in the Grosseto Province within the boundaries of Maremma Regional Park, and another much smaller population that was recently discovered in the Livorno Province (Bertacchi et al., Citation2005; Foggi et al., Citation2008b; Viciani et al., Citation2011). We conducted surveys in both areas, the results of which are shown in Table .
Table 2. Limonium etruscum communities. rel. 1-8: Limbardo crithmoidis-Limonietum estrusci ass. nova. rel. 9-13: Limbardo crithmoidis-Limonietum estrusci var. with Parapholis incurva. rel. 14: Very degraded community dominated by Tamarix gallica and Elymus athericus. Tableau II Communauté à Limonium etruscum. rel. 1-8: Limbardo crithmoidis-Limonietum estrusci ass. nova. rel. 9-13: Limbardo crithmoidis-Limonietum estrusci var. avec Parapholis incurva. rel. 14: cénose très dégradée dominée par Tamarix gallica et Elymus athericus.
Coenoses in the Grosseto location (rel. no. 1-8, shown on the left in Table ) cover about 2 hectares (Viciani et al., Citation2011), with an ecological optimum in high salinity shallow ground depressions where sand and silt soils merged (Lanfranco, Citation2008), which are humid for long periods and dry in the summer. These coenoses are mainly located between embryonic shifting dunes, characterized by Elymus farctus and areas of shrubby vegetation characterized by Juniperus macrocarpa, mainly on mobile dunes where Ammophila arenaria is absent. These communities are similar to associations with L. glomeratum found in Sardinia (Biondi et al., Citation2001a) and other Limonium-dominated coenoses of Corsica (Géhu & Biondi, Citation1994) and Mediterranean France (Braun Blanquet et al., Citation1952; Géhu et al., Citation1992). These communities are attributed to a new association named Limbardo crithmoidis-Limonietum etrusci ass. nova hoc loco (holotype, rel. no. 8 in Tab. II), characterized by L. etruscum and several differential species that indicate the specific ecological site conditions, including Sporobolus virginicus (silt-sand soils), Parapholis filiformis (dry salty soils), Limbarda crithmoides, Linum maritimun and Carex extensa (periodic submersion in brackish water). The relationship between Limbarda crithmoides and L. etruscum was also observed by Colombini et al. (Citation2008). The Maremma communities will probably disappear within a few years, unless the current features of the coastal system are conserved (Scapini, Citation2010).
The Livorno L. etruscum communities (rel. no. 9-14, shown on the right in Table ) cover a small area of less than 300 square meters (Viciani et al., Citation2011) and are clearly residual. They are located only a few meters from the shoreline on a dune belt that is partly artificially-shaped, where areas of low Tamarix gallica cover alternate with small open spaces, before the sclerophyllous maquis becomes dominant. Surveys conducted on this site report an altered and impoverished flora compared with the Grosseto coenoses, and a degraded variant with Parapholis incurva and other species is identified. Increased Tamarix cover appears to promote dynamic processes which lead to herbaceous species become dominant. Elymus athericus in particular, tends to become dominant (rel. no. 14 in Table ). L. etruscum probably inhabited a larger sandy belt on the coasts south of Livorno in the past, which were reduced by marine shoreline erosion and the use of dunes for forest plantations, tourism and other anthropic infrastructure.
Conclusions
From a syntaxonomical point of view the new association Limbardo crithmoidis-Limonietum etrusci can be attributed at a higher syntaxonomical level to the Limonietalia order, but some difficulties exist at the alliance level. Géhu and Biondi (Citation1995) split Limonietalia into four alliances on a synchorological basis. These four alliances are well characterized in the Iberian sector (Costa & Boira, Citation1981; Rivas-Martinez & Costa, Citation1984; Llorens, Citation1986; Cruz Rot, Citation2009) and in Mediterranean France (Braun Blanquet, Citation1931; Braun Blanquet et al., Citation1952; Molinier & Tallon, Citation1965, Citation1970; Géhu et al., Citation1992; Argagnon, Citation2008). Biondi et al. (Citation2001a) established a further alliance, Triglochino barrelieri-Limonion glomerati, which is endemic to Sardinia and characterized by several endemic Limonium species. Rivas-Martinez et al. (Citation2002) suggested five alliances, because they included Limoniastrion monopetali in the Limonietalia, which was previously attributed to Sarcocornietalia fruticosae. However, this amendment does not fundamentally alter the existing scheme. Perhaps the most suitable alliance for Tuscan coenoses, from a synchorological viewpoint, might be Limonion confusi (= Limonion gallo-provincialis, recorded in Corsica by Géhu & Biondi, Citation1994), semi-arid sea-lavender communities characteristic of North-Western Mediterranean coasts. L. confusum was originally considered as a form of “collective species” (Pignatti, Citation1972), and Limonion confusi is now used to refer to several endemic Limonium species (Rivas-Martinez et al., Citation2002), which makes it inappropriate for the Tuscan coenoses. The synoptic grouping table for the North-Mediterranean coenoses (Table ) shows that the only possible solution is to establish a new alliance (possibly only of local importance) that is endemic of Tuscan coasts, which we refer to as Limonion etrusci all. nova hoc loco (type: Limbardo crithmoidis-Limonietum etrusci ass. nova hoc loco), with L. etruscum as the characteristic species.
Syntaxonomic scheme
SALICORNIETEA FRUTICOSAE Br.-Bl. & Tüxen ex A. & O. Bolòs 1950 nom. mut. propos.
Table 3. Mediterranean salt steppe (Limonietalia) synoptic chart of Northern Mediterranean coastal communities. Tableau III Tableau synoptique des Limonietalia des côtes de la Méditerranée septentrionale.
Limonietalia Br.-Bl. & O. Bolòs 1958
Limonion etrusci all. nova hoc loco
Limbardo crithmoidis-Limonietum etrusci ass. nova hoc loco
Limonium narbonense communities
Other syntaxa quoted in the text
Crithmo-Staticetea Br.-Bl. in Br.-Bl., Roussine & Nègre 1952
Juncetalia maritimi Br.-Bl. ex Horvatic 1934
Juncetea maritimi Br.-Bl. in Br.-Bl., Roussine & Nègre 1952
Limoniastrion monopetali Pignatti 1953
Limonion confusi (Br.-Bl. 1933) Riv.-Mart. & Costa 1984
Limonion gallo-provincialis Br.-Bl. 1931
Sarcocornietalia fruticosae Br.-Bl. 1933 nom. mut. propos.
Triglochino barrelieri-Limonion glomerati Biondi, Diana, Farris & Filigheddu 2001
Related Research Data
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