Biogeographia vol. XX VII - 2006 (Pubblicato il 30 dicembre 2006) Biogeografia dell’Appennino centrale e settentrionalez trenfanni dopo Proposta cli reti ecologiche sulla base della biopermeabilita Vegetazionale (fitopermeabilita): il caso del Friuli Venezia Giulia ENRICO BRESSAN*, LIVTO POLDlNI** *Ur2iz/ersitiz degli studi di Yitieste, Dzpartiinento iii Biolagiiz, 1/izl E. Wiss 2, 34127 Yiieste (Italy); e—mzzi[: ebresszzn @units. it **Uniz/ersizfil degli studi di Fieste, Dipizrzfimemfo iii Bio/agizz, 2/izz L. Giorgieri J 0, 34127 Pieste (Italy); e-mail: p0[dim'@imits. it Key words: protected areas, ecological corridors, phytopermeability, Natura 2000, phytosociological progression SUMMARY In the Italian project “National Ecological Network: for the conservation of vertebrates” we tried to implement the ecological network on actual data. related to biological and ecological requirements of different vertebrates species. Animal biopermeability is defined as the capability of a living organism to pass through a natural or artificial structure. According with this definition, we guess that in an ecological corridor, vegetation structure plays the fundamental role; thus it is necessary to introduce the concept of vegetal or vegetational biopermeability in ecological networks. We refer to phytopermeability concerning vegetational cover and considering it as theoretical basis to characterize a widespread network of ecological corridors joining naturalistic areas of major interest in a specific ter1'ito1y.The definition of phytopermeability is based on floristic, structural and therefore functional aflinity of the plant community in the territory. The proposed method is based essentially on the analysis of the vegetation, whose phytosociological associations have been hierarchically ordered according to the “phytosociological progressionq. This progression reflects the affinities of floristic composition and also the increasing complexity of the interrelations between the biological forms and therefore the increased efliciency in the uses of the local resources. The phytosociological progression is represented by a sin—system that codifies the succession of the vegetation types (from the most primitive to the most evoluted). This sin—system allows to calculate an index ofaflinity between the single floristic communities by identifying areas where ecological corridors, that minimise the cost of species transfer, can be located. The ecological corridors were elaborated using algorithms already implemented in GIS—GRASS. INTRODUZIONE Il monclo scientifico, agli inizi degli afini ’80, ha proposto come strumento di possibile strutturazione del territorio per preservate la biodiversita la “rete ecologica”. Con questo termine si indica una rete fisica di aree centrali, collegate cla corridoi e sostenute da zone cuscinetto, per facilitate la dispersione e la migrazione delle specie ai fini della conservazione della natura, dentro e fuori le aree protette. Si era