«Abstract Frignani, F., Landi, M., Angiolini, C., Boddi, M. & Selvi, F.: Floristic richness and phytogeography of the “Torrente Trasubbie” nature ...»
F. Frignani, M. Landi, C. Angiolini, M. Boddi & F. Selvi
Floristic richness and phytogeography of the “Torrente Trasubbie”
nature reserve (S-Tuscany, Italy)
Frignani, F., Landi, M., Angiolini, C., Boddi, M. & Selvi, F.: Floristic richness and phytogeography of the “Torrente Trasubbie” nature reserve (S-Tuscany, Italy). — Fl. Medit. 17: 65-96.
2007. — ISSN 1120-4052.
The results of a floristic survey carried out in the “Torrente Trasubbie” nature reserve in Southern Tuscany (Grosseto province) are reported and briefly discussed. Firstly, a brief description of the geomorphology, climatic and vegetation of the area is given. Secondly, the list of the vascular flora is reported, which was based on field researches and herbarium material. This list includes 684 species belonging to 85 families and to 358 genera; 662 taxa are native or naturalized, whereas 28 are introduced species. The biological spectrum shows a comparable proportion of therophytes (238, 36.4%) and hemicryptophytes (240 species, 36.6%) suggesting a transition between the flora of coastal areas of southern Tuscany and that of inner mountain systems. However, the chorological analysis reveals the dominance of Mediterranean species. There are 11 endemics and a number of taxa of phytogeographical relevance at the regional and national level. The data indicate that the Torrente Trasubbie is an important area for the conservation of a complex environmental mosaic which contains a fairly high level of floristic biodiversity.
Key words: Flora, Geomorphology, Biological forms, Vegetation.
Introduction The “Torrente Trasubbie” Site of Regional Interest (S.I.R.) lies in the Grosseto province, Scansano municipality (Central Italy), and was established by the Tuscan Regional Law 56/2000 to safeguard the vast watercourse and the areas along its banks of a particular natural area in the Tuscan Maremma.
This was done in view of the bioecological and conservation importance of the different habitats existing in this biotope, which considerably outweighs their incidence on the national territory in terms of surface. The S.I.R. analysed here comprises a fine mosaic of riparian brushwoods, shrublands, garrigues and grasslands, to which are linked numerous ecotonal areas of great importance for animal life too. Recent vegetation surveys (Angiolini & al. 2005a) revealed the presence of particular types of plant communities and habitats, some of which are of communitarian interest according to the Directive EEC 66 Frignani & al.: Floristic richness and phytogeography of the “Torrente...
92/43. This is the case, for example, ofthe meadows of graminoid and annual grasses (Thero-Brachypodietea, Helianthemetea), the phytocoenoses of suffrutices with predominance of Santolina etrusca and Helichrysum italicum (Rosmarinetea), the hygrophilous communities of Nanocyperion and the riparian woodlands of Alnus glutinosa.
From the floristic viewpoint, however, the Trasubbie area has still to be analysed in detail like most of the inner parts of the Tuscan Maremma (Angiolini & al. 2005b). The first botanical information on the Scansano territory dates back to the late 18th century, when Santi (1798), during his second trip to Mount Amiata, drew up a short list of the species in the area. More recently, detailed vegetation studies were carried out on the S.I.R., and these provided additional floristic information which underscored the botanical relevance of the biotope (Scoppola & Angiolini 1997a, b; Angiolini 1998; Angiolini & De Dominicis 2001; Angiolini & al. 2004a, b). A synthetic description of the site has also appeared in a recent survey on natural biotopes in the Grosseto province (Selvi & Stefanini 2005). Such preliminary data encouraged us to undertake a more detailed census of the floristic diversity, to provide a basis for conservation actions which may ensure in time the safeguard of this peculiar stretch of Tuscany’s natural landscape.
The Torrente Trasubbie originates in the area between Poggio le Sassaie (1,080 m a.s.l.) and Mount Buceto (1,152 m), within the “Monte Labbro-Alta valle dell’Albegna” Site of Communitarian Importance in the central-eastern part of the Grosseto province, southern Tuscany (Fig. 1). It is about 24 km long, runs E/NE-W and joins the river Ombrone at an altitude of 18 m above sea level. Its main tributary is the torrent Trasubbino which, after its confluence with the Fosso Senna, runs leftwards through the alluvial plain. The total surface of the S.I.R. is about 1,381 ha and includes the beds of the three main streams Trasubbie, Trasubbino and Senna from a maximum altitude of 330 m to a minimum of 35 m. The outer edge of the area under consideration corresponds to the outer part of the riparian strip; therefore, the entire site takes the form of narrow, long strips, parallel to the watercourses.
The Trasubbie biotope is characterized by the same aspect of Calabrian, Sicilian and eastern Alpine “fiumaras”. Its main bed reaches the remarkbale width of c. 800 m and is marked by a network of shallow streams with clean water. These are almost completely dry during the summer but experience sudden, violent floods in early spring and autumn. This kind of bed with braided streams is characterized by severe erosion in its upper part, whereas in the lower part the load of detritus is higher than that the torrent can carry. The excess material accumulates along the wide bed, thus leading to the sedimentation of large amounts of gravelly and pebbly material and to a process known as “aggradation” (Castiglioni 1991). Transport and sedimentation dynamics lead to the rapid growing of rises and fluvial bars which progressively increase in volume to form more stable and mature levels referred to as river terraces. These tend to change, to grow rapidly or even to be eroded by the stream current. The morphology of the fluvial bed is therefore subject to a severe dynamics over time, accounting for the variability of bed’s edges, surface and shape. This explains why the administrative boundaries indicated here could change in a not-too-distant future.
Flora Mediterranea 17 — 2007 67 Fig.1. The study area in (Tuscany, Central Italy).
Geological outline In the S.I.R.
area the following lithotypes can be found (Italian Geological Service 1969, Sheet 128, Grosseto):
Present and recent alluvia – Pebbly, sandy and clayey sediments are by far the predominant typology. These sediments come into contact with sandy lacustrine marls and clays. Alluvial deposits are located in the vast downstream torrent bed up to the escarpments of the higher and older terraces.
Conglomerates – These are either loose or weakly cemented by a sandy-clayey matrix.
Sands and clays – Marine and deltaic Pliocene sediments represented by sands, sandstones and marly sands. They are located in the upstream part of the site and are in contact with the alluvia, but they cover a limited area.
Sandstones – They are mainly represented by arenaceous shales and clayey-arenaceous shales (Tuscan Series) with clayey, siliceous sometimes calcitic cement.
Calcareous-marly-arenaceous flysch – Light marly limestones, marly shales, slates associated with compact, arenaceous limestones, in contact with the alluvia; limited covering.
68 Frignani & al.: Floristic richness and phytogeography of the “Torrente...
The thermo-pluviometric data refer to the 1951-1980 period (Barazzuoli & al. 1993) for the Granaione, Cinigiano and Cana climate stations which are nearest to the biotope (Table 1). The climate is generally mesothermic but there is a main east-west gradient of change occurs in terms of increasing aridity, from humid with moderate aridity in the summer to subarid with high aridity in the summer (Thornthwaite 1948). The lower part of the biotope area is included in the mesomediterranean belt (climacic vegetation referable to Quercion ilicis) whereas the upstream area is included in the hilly/oceanic belt (climax vegetation referable to Lonicero-Quercion pubescentis) (Biondi & Baldoni 1994).
The vegetation along the watercourse is mainly composed of a mosaic of hygrophilous and xerophilous phytocoenoses strongly differing in ecological, physionomical and floristic terms. Native grasses and shrubs colonizing the pebbly banks cover around 28% of the area. The slow-flow bed is characterized by perennial, pioneer herbaceous formations especially Dittrichia viscosa referable to Agropyretalia intermedii-repentis, by small therophytic meadows with Brometalia rubenti-tectorum species, as well as by a more or less continuous belt of willow shrubs referable to Salicetalia purpureae.
The floodplain’s most stable terraces are colonised by glareicolous garrigues with dominance of Santolina etrusca and Helichrysum italicum (such aspects are referable to Rosmarinetalia), which represent the most typical habitat of the S.I.R. In contact with these garrigues there are “savannoid” steppes with dominance of Ampelodesmos mauritanicus and mediterranean sclerophyllic formations referable to the Pistacio-Rhamnetalia alaterni order. Paliurus spina-christi scrubs, referable to Prunetalia spinosae, are fairly Table 1. Temperature and rainfall.
Average monthly and annual temperature (°C)
frequent. Deciduous, broad-leaved woods cover 32% of the area and are more represented in the upper part of the Trasubbino valley. On the outer, flat terraces where soil is more developed and deep there are small, scattered, hygrophilous woods of Populetalia albae.
The potential, woody, slope vegetation is characterized by formations referable to Quercetalia pubescenti-petraeae; here there is a dominance, to a different extent, of Quercus pubescens, Quercus cerris and Ostrya carpinifolia, while evergreen woods of Quercetea ilicis can be found in the downstream area on south-facing slopes. Of great interest are hygrophilous, riparian woods on the outer alluvial terraces with predominance of Fraxinus angustifolia subsp. oxycarpa and badland (calanchi) formations made of Pliocene clays (Angiolini & al. 2004a, b).
The floristic list is based on information from the recent vegetation surveys mentioned above and on field collections carried out during the years 2000-2005. The exsiccata, deposited in the Herbarium Universitatis Senensis (SIENA), the Herbarium Centrale Italicum (FI) and the Herb. Selvi, were studied using the main national and European standard Floras (Fiori 1923-29; Pignatti 1982; Tutin & al. 1964-1980, 1993) as well as monographic works and revisions of single groups, when available. The systematic ordering of the floristic list follows Pichi Sermolli (1977) for Pteridophyta, Cronquist (1981) for Magnoliopsida and Dahlgren & al. (1985) for Liliopsida; congeneric species are listed in alphabetically. Nomenclature is in accordance with the International Code of Botanical Nomenclature (Greuter & al. 2000). Med-Checklist (Greuter & al. 1984-89), Flora Europaea (Tutin & al. 1968-80, 1993) and Flora d’Italia (Pignatti 1982) were used as references, whereas Rossi (2002) was followed for Orchidaceae. Authors’ names are abbreviated according to Brummitt & Powell (1992).
Sub-specific categories were reported only when different from the nominal subspecies. Each taxon is followed by: life-form, chorological type, habitat and frequency in the area. Life-forms, verified in nature and on the specimens, are expressed using Pignatti’s acronyms (Pignatti 1982), based on Raunkiaer’s classification (Raunkiaer 1934). Chorological types are those proposed by Pignatti (1982). Non-native taxa are marked by “+”; they are divided into adventitious i.e. naturalised plants after accidental introduction and cultivated, i.e. plants deliberatly introduced but not capable of spread without human assistance (Viegi & al. 1974); both types are excluded from the biological and chorological spectra. Preferential vegetation habitat type is expressed as follows: PT small therophytic meadows, PA small hemicryptophytic meadows of the torrent bed, Q deciduous oak-woods and mixed woods of deciduous, broad-leaved trees, I hygrophilous woods and scrubs, M evergreen maquis and Quercus ilex woods, G open garrigues and river terraces, R rocky sites, AU humid sites, S synanthropic environments.
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