Floristic Traits and Biogeographic Characterization of the Gennargentu Massif (Sardinia)

Abstract Bacchetta, G., G. Fenu, R. Guarino, G. Mandis, E. Mattana, G. Nieddu & C. Scudu (2013). Floristic traits and biogeographic characterization of the Gennargentu massif (Sardinia). Candollea 68: 209–220. In English, English and French abstracts. A study on the vascular flora of the Gennargentu Massif (Central-Eastern Sardinia) is presented. According to our results, the flora consists of 948 taxa: 686 species, 249 subspecies, 10 varieties and 3 hybrids, belonging to 97 families and 427 genera. Three taxa are new findings for the flora of Italy and eight for that of Sardinia. Life form analysis revealed, in particular, dominance of 35.65% hemicryptophytes, 34.6% therophytes, 12.13% geophytes and 11.6% (nano)-phanerophytes. As concerns chorology, the Mediterranean element is largely prevailing (68.14%), mainly represented by circum-Medit. (29.1%) and Euro-Medit. (23.07%). Endemics are 14.87% of the whole flora (141 taxa), with a large prevalence of Sardo-Corsican (39.01%) and Sardinian taxa (35.46%), i.e. 74.47% of the total. Due to the high number of taxa (9) of Gennargentu exclusive endemics and the geologic and geomorphologic peculiarities, it is here proposed a biogeographic classification for these territories serving to the identification of an auto nomous sector.


Introduction
The Mediterranean basin has been recognised as one of the 34 most important biodiversity hotspots, also because of its high number of endemic plant species (MITTERMEIER & al., 2004). This area not only constitutes a refuge for many relic species, but the relatively short distance of many islands and peninsulas promotes floristic exchanges and active plant speciation. MÉDAIL & DIADEMA (2009) identified the Central-Northern Sardinia as one of the 52 putative floristic refugia within the Mediterranean, i.e. places facilitating the long-term persistence of a species (one or more glacial-interglacial cycles) or of one or more of its meta-populations in a well-defined geographical area (e.g. mountain range, gorge). Sardinia, with its 24,090 km 2 , is the second-largest island in the Mediterranean Sea. The prolonged isolation and high geological diversity created a wide range of habitats rich in endemic species, particularly on its mountain massifs, where the insularity is strengthened by the altitude and diversity of terrains (MÉDAIL & QUÉZEL, 1997). The Sardinian flora consists of 2408 taxa including 2295 species (CONTI & al., 2005) 168 of which are exclusive endemics (BACCHETTA & al., 2012b).
According to the biogeographic classification of the Mediterranean region proposed by RIVAS-MARTÍNEZ & al. (2002), the Italo-Tyrrhenian province is composed by three subprovinces: the Sardinian, the Corsican and the Tuscano-Calabrian. Owing to the many similarities, not only in the floristic aspects, it is here preferred to recognize the rank of biogeographical province to Corsica and Sardinia, in the frame of an Italo-Tyrrhenian superprovince extended to all over the western coast of the Italian Peninsula, from Tuscany to Calabria, as formerly proposed by LADERO ALVAREZ & al. (1987). The Sardo-Corsican province, on the contrary, can be furtherly divided into a Sardinian and a Corsican subprovince, as stated by BACCHETTA & PONTECORVO (2005). These authors, basing on their studies on the vascular endemic flora of Sulcis-Iglesiente, conferred the rank of biogeographic sector to these territories. Furthermore, a Sinisico subsector (included in the Campidano Sector) has been identified by FENU & BACCHETTA (2008) for the Sinis Peninsula (Central-Western Sardinia), while FENU & al. (2010) proposed a new biogeographic sector for the Supramontes region (Central-Eastern Sardinia). Other parts of the island, including Gennargentu massif, still remain poorly investigated from a biogeographic viewpoint.
Gennargentu is the main mountain complex of Sardinia and since the beginning of the 18 th century it became a popular destination for botanical investigations (MORIS, 1827(MORIS, , 1837(MORIS, -1859BARBEY, 1885;MARTELLI, 1896MARTELLI, -1904HERZOG, 1909;SCHMID, 1933;DESOLE, 1948DESOLE, , 1966ARRIGONI, 1966ARRIGONI, , 1986BRULLO & al., 2001), that led to the description of several new taxa (PIGNATTI & FEOLI, 1974;ARRIGONI & al., 1977ARRIGONI & al., -1991PIGNATTI & al., 1980;BACCHETTA & al., 2000 and to the analysis of the conservation status of some threatened taxa (FENU & al., 2011(FENU & al., , 2012. In spite of the relevant information provided by the abundant literature, an organic review on the vascular flora of Gennargentu was still missing, as well as floristic checklists for the whole massif or single parts of it. Furthermore, relatively big portions of this territory were little known or even unexplored. For these reasons, up to now, a detailed biogeographic framework has never been proposed for the concerned area.
Aims of this work were a comprehensive checklist of the vascular flora of Gennargentu and the analysis of its endemic component, in order to set the area in the Sardinian biogeographic subprovince.

Study Area
Gennargentu ( Fig. 1) is located in the central-eastern part of Sardinia and borders the "Barbagia di Ollolai" to the North, the "Mandrolisai" to the North-West and West, the "Sarcidano" and "Barbagia di Belvì" to the South, the "Ogliastra" to the East, the "Supramontes of Urzulei and Orgosolo" to the North-East. The study area has a surface of 50,000 ha and consists of a system of summits and windy ridges at 1400-1500 m, with four culminations at more than 1800 m: Punta La Marmora (1834 m Metamorphic rocks are by far the most represented outcrops. They include Carboniferous metasiltstones and metasand stones, regularly superimposed to schists, limestones and dating, respectively, to Devonian-Silurian and Ordovician (CARMIGNANI & al., 2001). As by-products of the late Hercinic orogeny, intrusions of granites and porphyrites are also frequent (CARMIGNANI & al., 2001). In the area of Arcu Correboi, thick Ordovician quartzitic and foliated silicates are interstratified, with Devonian-Silurian black schists and limestones. The study area covers the whole layered structure that identifies the Gennargentu lithostratigraphic unit (CARMIGNANI & al., 2001).
According to the Rivas-Martínez's bioclimatic classification, most of the Gennargentu massif has a temperate-submediterranean climate, with thermotypes ranging from the lower supratemperate to the lower orotemperate, and ombrotypes from the upper subhumid to the upper humid. The Mediterranean climate is only found on the eastern and southern slopes of the massif, with a lower supramediterranean thermotype and ombrotype ranging from the upper subhumid to the lower humid (BACCHETTA & al., 2009a).

Methods
Years of floristic researches have been carried out between 2004 and 2011; field trips were effectuated from February to November. Specimens and seeds collected in the field are stored in CAG and in the Sardinian Germplasm Bank (BG-SAR), respectively. Bibliographic and herbariological researches have been fulfilled in BOLO, CAG, CAT, FI, NAP, PAL, RO, SASSA, SS, TO, W, Z.
Growth and life forms have been determined in the field, following the classification of RAUNKIAER (1934), and expressed with the abbreviations proposed by PIGNATTI (1982).
In addition to the consulted floras, chorotypes refer to the classification proposed by BRULLO & al. (1996). For the chorological classification of the endemics, the nomenclature proposed by ARRIGONI & TOMMASO (1991) and modified by BACCHETTA & PONTECORVO (2005) is followed.
For the non-native species, the place of origin is reported, as well as the abbreviations on the "status" proposed by RICHARDSON & al. (2000) and modified by PYŠEK & al. (2004): "Cas ϭ casual", "Nat ϭ naturalized", "Inv ϭ invasive".
Taxa known from literature but not found during our field investigations have not been considered in the floristic analysis.
For the biogeographic analysis of the investigated area, the methodological framework proposed by RIVAS-MARTÍNEZ (2007)
The Sardo-Corsican elements (Fig. 5) prevail (39.01%), followed by the Sardinian ones (35.46%) and by the Italo-Tyrrhenian (18.44%). The last group includes taxa in common with the Tuscan Archipelago (7.8%) and some others ranging up to limited portions of the western coast of the Italian peninsula and Sicily (10.64%).

Discussion
In the area of Gennargentu, corresponding roughly to 1% of Sardinia, more than 30% of the regional flora is occurring. Although the available floristic data do not allow to estimate species-area relationships, this high number of taxa, combined with more general considerations on the uniqueness of Gennargentu in terms of largeness and altitude highlight the floristic importance of this area.
The floristic richness of Gennargentu can be explained hypothesizing that along the Quaternary age, the less drastic climate changes on large Mediterranean islands favoured the local persistence of high plant richness and the co-existence of distinct genetic lineages (VALIENTE BANUET & al., 2006;MEDAIL & DIADEMA, 2009), confirming the identification of this area as one of the Mediterranean putative refugia. The observed pattern in plant family distribution, which is only partially correlated with the pattern of endemic species, may testify that Gennargentu acted as a "climatic island" during the Quaternary climatic variations. Floristic changes were more severe and drastic in the lowlands and re-colonisation was particularly important for shaping the modern floras at lower altitudes. Not all taxa were able to recolonise and the empty niches were filled by new adaptive radiation of migrating taxa, with a strong tendency towards the annual life strategy (GUARINO, 2006). The result is that families are generally larger, but with fewer endemic species in the lowlands than in the summit areas of Gennargentu, where the elevation facilitated the survival or, eventually, an independent adaptive radiation of locally surviving taxa. For example, a high potential for adaptive radiation of the Ranunculaceae may be seen in the fact that this family has a significant number of endemic species on Gennargentu, even if it does not account for the most representative families in that area, nor in the whole Sardinian flora. Likewise, the Asteraceae seem to have a strong potential for both migrations and local adaptive radiation, whereas the Poaceae are remarkable for a high migration potential but may have a low potential for local, independent adaptive radiation. Families like Fabaceae, Asteraceae and Euphorbiaceae were likely to be able to diversify on the Gennargentu summits not only in the Pleistocene, but also in the Post-Messinian phase.
The role of Gennargentu as a "climatic island" was also confirmed by the life form analysis where the ratio between hemicryptophytes and therophytes is much higher than in the rest of Sardinia (28.1% and 39.9% for H and T, respectively;BOCCHIERI, 1995). Even the number of nano-phanerophytes is well above the average value for Sardinia (8.8%;BOCCHIERI, 1995) The percentage of geophytes is also pretty high; this is probably linked to the pastoral land-use of the whole area, frequently affected by periodical fires as for the whole Island (12.1% ; BOCCHIERI, 1995). Chamaephytes display values slightly under the average value for Sardinia (8.1% ; BOCCHIERI, 1995) and the few hydrophytes testify the lack of backwater on Gennargentu.
In the chorologic analysis, the relatively high percentage of palaeotemperate elements outlines the temperate-submediterranean bioclimate in the summit areas of the massif, as well as on its northern slopes. The low percentage of nonnative taxa denotes the high naturalistic value of the inspected area and suggests that the mountain flora of Sardinia is probably less prone to competition by allochtonous taxa (BACCHETTA & al., 2009b).
Sardinia is well known for its richness in endemic taxa, due to the isolation and high topographic diversity (MÉDAIL & QUÉZEL, 1997). The Gennargentu massif, even if its elevation is not comparable with that of the Corsican mountains and has never been affected by glacial perturbation, hosts several distinctive ecological niches as highlighted in the case of Lamyropsis microcephala (Moris)  In particular, rocky habitats and windy summit areas, in spite of their limited extension, form a very important reservoir for the local biodiversity (MÉDAIL & QUÉZEL, 1997). The high percentage of Sardinian endemics (35.46%) and, within these, of the taxa exclusively growing on Gennargentu (6.38%) testifies the floristic autonomy of the massif. The relatively high percentage of Sardo-Corsican endemics (39.01%), as well as of endemic taxa in common with the Tuscan Archipelago (7.8%) turns out to be so high because of the prevalence of siliceous rocks, that enhances the floristic affinity of Gennargentu with the Corsican and the Ilvensian territories (BACCHETTA & PONTECORVO, 2005). On the other hand, in the Sardinian areas where limestones and carbonatic rocks in general prevail, and particularly in the so-called "carbonate-metalliferous ring" (i.e. S-W Sardinia), or in the Supramontes area (i.e. C-E Sardinia, just around Gennargentu), the number of Sardinian exclusive endemics tends to be higher than in Gennargentu (BACCHETTA & PONTECORVO, 2005;FENU & al., 2010).
The nine endemic taxa in common with the Balearic Islands, added to the 8.51% of West-Mediterranean elements, confirmed the biogeographical affiliation of Sardinia to the socalled "W-Mediterranean subregion" (BACCHETTA & PON- TECORVO, 2005). The 11 taxa in common with Corsica and the Tuscan Archipelago justify the biogeographical identity of an Italo-Tyrrhenian Superprovince, as proposed by LADERO ALVAREZ & al. (1987) and followed by BACCHETTA & al. (2012a).
In conclusion, the overall floristic richness of Gennargentu massif, determined by its ecological insularity and the richness of its endemic flora, highlighted the peculiarity of this territory and its identification as one of the Mediterranean putative "refugia", as stated by MEDAIL & DIADEMA (2009), justifying the set up of an autonomous biogeographic sector.