South-eastern Sicily, otherwise called Hyblean district, is geologically made of a calcareous plateau of Ceno-Mesozoic origin which is interrupted by volcanic formations in the mountains and in the northern part. The southern, eastern and northern sides of the plateau degrade towards the Sicilian Canal, the Ionic Sea and the Catania Plane, respectively. The north-western side is bordered by a Plio-Pleistocene transition area of sand and clay. The plateau is ploughed by several rivers in a sunburst pattern from Mt. Lauro (986 m), which is the highest part of the area. The Hyblean district is the most anciently part of Sicily colonized by man. This millenary presence has caused alterations and the disappearance of the original forest cover, which is still present, but with few fragmented strips. Consequently, the identification of climax vegetation results to be sometimes hard. In this paper we perform a bioclimatic study of the area according to Montero de Burgos & Gonzales Rebollar method (1983) based on a set of indices or Bioclimatic Intensities, among which there is the potential Bioclimatic Intensities (IBP), the actual one (IBR), the free one (IBL), the dry one (IBS), the conditioned one (IBC) and the cold one (IBF). The IBP estimates the maximum primary productivity of a climate without factors limiting plant growth; IBR estimates the actual productivity taking place when water availability is not sufficient to compensate for evapotranspiration requirements; IBL estimates forest productivity; IBS and IBF, finally, estimate the duration and intensity of vegetation inactivity periods due to summer draught or winter harshness. Based on the monthly values of the IBs, 33 stations in south-eastern Sicily were classified according to the hierarchical method using the dissimilarity coefficient of Bray & Curtis (1957) and the complete linkage technique. The results of the cluster analysis allowed us to gather the 33 stations of the Hyblean District into two groups, each divided, in turn, into three subgroups. In all the 6 subgroups correspond to the geographical division of the district into homogenous phytoclimatic areas, which shows clearly how the south-western area is well differentiated from the eastern one. Starting from the top of the Hyblean mountains, two different bioclimatic gradients develop, the one along the southern and south-western coastal line, and the other towards the north-eastern coast. Generally, stations in the south-western area result to be characterized by longer periods of draught, whereas those in the eastern area have lower primary productivity in winter months. The mountainous area is distinguished by the presence of IBF in winter or, anyway, by low IBL values. Distinctive phytoclimatic conditions characterize the Buccheri area which results thus to be different from all others. Next to Buccheri, on the top of Mt. Lauro, we find grasslands of Hypochoeridio-Lotetum conimbricensis Brullo, Grillo & Terrasi 1976, which are very close in ecology and floral composition to Cynosuro-Leontodontetum siculi Brullo & Grillo, 1978, which is largely represented on the Nebrodi range (northern Sicily). The potential vegetation of Buccheri area is deciduous oak forests of Mespilo-Quercetum virgilianae Brullo & Marcenò 1984; according to some authors, the uppermost area of Mt. Lauro could be interested by Turkey oak (Quercus cerris L.) woods of Arrhenathero nebrodensis-Quercetum cerridis Brullo, Minissale, Signorello & Spampinato 1996. The potential natural vegetation of the area immediately south-west of Buccheri, which is characterized by rather higher winter temperatures, is represented by Mespilo-Quercetum virgilianae although forest phytocoenoses belonging to Oleo-Quercetum virgilianae Brullo 1984, lacking the evergreen schlerophyll component of Pistacio-Rhamnetalia alterni Rivas-Martinez 1975, can be found below 600 m of altitude. Starting from this area and proceeding along the two sides, two phytoclimatic gradients develop. The hilly area of the south-western side is characterized by Oleo-Quercetum virgilianae Brullo 1984, although under special soil conditions, namely the sand substrate, thermo-xerophyll cork woods develop of Stipo bromoidis-Quercetum suberis Barbagallo 1983. Also the potential vegetation of the hilly area of the eastern side can be referred to Oleo-Quercetum virgilianae, although on volcanic substrates it can take special features and be associated to Quercus suber. Furthermore, in the eastern-most area, fragmented Holly oak groves of Doronico-Quercetum ilicis Barbagallo, Brullo & Fagotto 1979 are present, probably due to the damp winds from the Ionic Sea. As far as the low hill areas are concerned, on the south-western side the potential vegetation can be ascribed to Oleo-Quercetum virgilianae although the edaphic-climax vegetation corresponding to outcropping marl on Ippari (Vittoria) basin can be ascribed to Thymo-Pinetum halepensis De Marco & Caneva 1985. The low-hill belt of the eastern side is interested by Oleo-Quercetum virgilianae and, under peculiar station conditions in Siracusa area by Doronico-Quercetum ilicis (Fichera et al. 1988 a). Finally, regarding the potential vegetation of coastal areas, thermo-xerophyll groves of Calicotomo-Rhoetum tripartitae Bartolo, Brullo & Marcenò 1982 characterize the south-western sector; Myrto-Lentiscetum (Molinier, 1954 em. O. Bolòs 1962) Rivas Martinez 1975, instead, is typical of the eastern sector. The bioclimatic analysis performed results to be useful to describe the general relationship between climate-vegetation. Several station parameters, connected to the geographical position, can modify the local topoclimatic conditions, thus allowing the development of phytocoenoses different from those taken as a reference for the relative phytoclimatic area.
Viene presentata l'analisi fitoclimatica della Sicilia sud orientale attraverso l'applicazione delle Intensità Bioclimatiche e dei Diagrammi Bioclimatici proposti da Montero de Burgos e Gonzales Rebollar (1983). L'analisi ha permesso di suddividere il territorio in aree omogenee a cui corrispondono quasi sempre differenti tipologie di vegetazione potenziale. Dall'area sommitale del comprensorio ibleo si sviluppano due diversi gradienti bioclimatici: uno, più termoxerico, segue il versante sud occidentale, mentre l'altro segue quello nord orientale. La vegetazione naturale potenziale dell'area sommitale può essere attribuita al Mespilo-Quercetum virgilianae Brullo e Marcenò 1984. Scendendo di quota, risultano progressivamente più rappresentate le formazioni forestali dell'Oleo-Quercetum virgilianae Brullo 1984 che, in base al versante ed alla quota, mostrano delle variazioni nella componente in sclerofille sempreverdi dei Pistacio-Rhamnetalia alaterni Rivas-Martinez 1975. Inoltre, in particolari condizioni legate al substrato geologico, si sviluppano tipologie vegetazionali edafoclimaciche peculiari. Lungo le fasce basso-collinari e litoranee, infine, la vegetazione potenziale è rappresentata dal Calicotomo-Rhoetum tripartitae Bartolo, Brullo & Marcenò 1982 sul versante meridionale e dal Mirto-Pistacietum lentisci (Molinier 1954 em. O Bolòs 1962) Rivas Martinez 1975 su quello orientale. Questo inquadramento, delineato a livello generale per le superfici del tavolato ibleo, trova tuttavia numerose variazioni determinate da peculiari condizioni stazionali.
Fitoclima della Sicilia sud-orientale
Terzi M;Perrino P;Tomaselli V
2006
Abstract
South-eastern Sicily, otherwise called Hyblean district, is geologically made of a calcareous plateau of Ceno-Mesozoic origin which is interrupted by volcanic formations in the mountains and in the northern part. The southern, eastern and northern sides of the plateau degrade towards the Sicilian Canal, the Ionic Sea and the Catania Plane, respectively. The north-western side is bordered by a Plio-Pleistocene transition area of sand and clay. The plateau is ploughed by several rivers in a sunburst pattern from Mt. Lauro (986 m), which is the highest part of the area. The Hyblean district is the most anciently part of Sicily colonized by man. This millenary presence has caused alterations and the disappearance of the original forest cover, which is still present, but with few fragmented strips. Consequently, the identification of climax vegetation results to be sometimes hard. In this paper we perform a bioclimatic study of the area according to Montero de Burgos & Gonzales Rebollar method (1983) based on a set of indices or Bioclimatic Intensities, among which there is the potential Bioclimatic Intensities (IBP), the actual one (IBR), the free one (IBL), the dry one (IBS), the conditioned one (IBC) and the cold one (IBF). The IBP estimates the maximum primary productivity of a climate without factors limiting plant growth; IBR estimates the actual productivity taking place when water availability is not sufficient to compensate for evapotranspiration requirements; IBL estimates forest productivity; IBS and IBF, finally, estimate the duration and intensity of vegetation inactivity periods due to summer draught or winter harshness. Based on the monthly values of the IBs, 33 stations in south-eastern Sicily were classified according to the hierarchical method using the dissimilarity coefficient of Bray & Curtis (1957) and the complete linkage technique. The results of the cluster analysis allowed us to gather the 33 stations of the Hyblean District into two groups, each divided, in turn, into three subgroups. In all the 6 subgroups correspond to the geographical division of the district into homogenous phytoclimatic areas, which shows clearly how the south-western area is well differentiated from the eastern one. Starting from the top of the Hyblean mountains, two different bioclimatic gradients develop, the one along the southern and south-western coastal line, and the other towards the north-eastern coast. Generally, stations in the south-western area result to be characterized by longer periods of draught, whereas those in the eastern area have lower primary productivity in winter months. The mountainous area is distinguished by the presence of IBF in winter or, anyway, by low IBL values. Distinctive phytoclimatic conditions characterize the Buccheri area which results thus to be different from all others. Next to Buccheri, on the top of Mt. Lauro, we find grasslands of Hypochoeridio-Lotetum conimbricensis Brullo, Grillo & Terrasi 1976, which are very close in ecology and floral composition to Cynosuro-Leontodontetum siculi Brullo & Grillo, 1978, which is largely represented on the Nebrodi range (northern Sicily). The potential vegetation of Buccheri area is deciduous oak forests of Mespilo-Quercetum virgilianae Brullo & Marcenò 1984; according to some authors, the uppermost area of Mt. Lauro could be interested by Turkey oak (Quercus cerris L.) woods of Arrhenathero nebrodensis-Quercetum cerridis Brullo, Minissale, Signorello & Spampinato 1996. The potential natural vegetation of the area immediately south-west of Buccheri, which is characterized by rather higher winter temperatures, is represented by Mespilo-Quercetum virgilianae although forest phytocoenoses belonging to Oleo-Quercetum virgilianae Brullo 1984, lacking the evergreen schlerophyll component of Pistacio-Rhamnetalia alterni Rivas-Martinez 1975, can be found below 600 m of altitude. Starting from this area and proceeding along the two sides, two phytoclimatic gradients develop. The hilly area of the south-western side is characterized by Oleo-Quercetum virgilianae Brullo 1984, although under special soil conditions, namely the sand substrate, thermo-xerophyll cork woods develop of Stipo bromoidis-Quercetum suberis Barbagallo 1983. Also the potential vegetation of the hilly area of the eastern side can be referred to Oleo-Quercetum virgilianae, although on volcanic substrates it can take special features and be associated to Quercus suber. Furthermore, in the eastern-most area, fragmented Holly oak groves of Doronico-Quercetum ilicis Barbagallo, Brullo & Fagotto 1979 are present, probably due to the damp winds from the Ionic Sea. As far as the low hill areas are concerned, on the south-western side the potential vegetation can be ascribed to Oleo-Quercetum virgilianae although the edaphic-climax vegetation corresponding to outcropping marl on Ippari (Vittoria) basin can be ascribed to Thymo-Pinetum halepensis De Marco & Caneva 1985. The low-hill belt of the eastern side is interested by Oleo-Quercetum virgilianae and, under peculiar station conditions in Siracusa area by Doronico-Quercetum ilicis (Fichera et al. 1988 a). Finally, regarding the potential vegetation of coastal areas, thermo-xerophyll groves of Calicotomo-Rhoetum tripartitae Bartolo, Brullo & Marcenò 1982 characterize the south-western sector; Myrto-Lentiscetum (Molinier, 1954 em. O. Bolòs 1962) Rivas Martinez 1975, instead, is typical of the eastern sector. The bioclimatic analysis performed results to be useful to describe the general relationship between climate-vegetation. Several station parameters, connected to the geographical position, can modify the local topoclimatic conditions, thus allowing the development of phytocoenoses different from those taken as a reference for the relative phytoclimatic area.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
