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Fitosociologia numero 42 (2)

pag. 3-13: Valutazione della qualità e dello stato di conservazione degli ambienti litoranei: l’esempio del S.I.C. “Penisola del Cavallino: biotopi litoranei” (Venezia, NE-Italia)

G. Buffa, D. Mion, U. Gamper, L. Ghirelli & G. Sburlino

Università di Venezia, Dipartimento di Scienze Ambientali, Campo Celestia 2737b, I-30121 Venezia; e-mail: buffag@unive.it

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abstract

Evaluation of quality and conservation status in coastal landscapes: the example of the Site of Community Importance “Penisola del Cavallino: biotopi litoranei”(Venice, NE Italy). Quality of coastal landscape has been estimated at two different scale: at the community level, we assessed a naturalistic value, by evaluating characteristics coming both from species (i.e. presence of endemic species) and from community itself (i.e. rarity). We also took into account the percentage of exotic and ruderal species on the total number of species of each community, as an indirect measure of alteration degree.
At the landscape level, we tried to value structural and functional integrity by evaluating spatial connectivity and contrast among patches. As the plant communities of foredunes show a typical spatial zonation, the two indices have been calculated along 27 transects perpendicular to the seashore. On the basis of a digital map of the area, we measured the gamma connectivity index along each transect; we assessed both “total connectivity”,
considering all the communities intersected by the transects, and “partial connectivity”, considering only the plant communities of foredunes, so describing spatial distribution model of coastal vegetation. Since on the backdune there is not a typical zonation of communities, we counted only the links between natural communities, considering anthropogenic communities as a break of natural landscape and of connectivity. In addition, we measured the contrast index; this index evaluates the change in environmental conditions going from one community (or patch) to the neighbouring one. The different patches are included and surrounded by a matrix, consisting of “nonhabitat” at different degree of alteration, that may function as an impenetrable barrier for individuals or, on the contrary, may favour movements. Thus, the surrounding matrix may significantly influence the effective isolation of habitat patches, rendering them more or less isolated than simple distance would indicate. For the contrast computation, we utilized the naturalistic value assessed to each community on the basis of the phytosociological data. Both indices point to the extreme fragmentation
of coastal landscape and to high vulnerability that characterizes all natural communities being they surrounded by a matrix highly contrasting. Conservation strategies should, then, concern natural habitat, their quality and their structural and functional integrity, but they should also consider the quality of surrounding matrix.

keywords

coastal landscape, community quality, contrast, North Adriatic, structural connectivity, transect