La viticoltura in Valchiavenna (SO): il progetto Pianazzola

Centered in the Alpine chain, Valchiavenna (Mera catchment area, Sondrio Province) could well represent a standard reference area for Quaternary geology and Alpine environment geomorphology. Also important here is the ancient cultural heritage: the man-made landscape. The latter corresponds to a combination of steep slopes, terraces and vineyards, which have been cultivated probably since the 11th century, although the quality of wine made of Chiavennasca (Nebbiolo) was always lower than that from nearby Valtellina (ZOIA, 2004). The area is located in the northern edge of Lombardy, close to Switzerland. Northern Valchiavenna encompasses two valleys, Val San Giacomo and Val Bregaglia/Bergell, which have been deeply cut respectively by Liro creek, originating from Spluga Pass and Mera/Maira river, from Maloja Pass, on the main Alpine watershed. This paper describes some characteristics of a site belonging to the Chiavenna municipality: Pianazzola, a small village at an elevation of about 750 m a.s.l., on southwards (dextral) slope of Bregaglia valley. Pianazzola lays just above the confluence of Liro in the Mera river: the former follows a dense swarm of NNW-SSE trending fractures, belonging to a regional tectonic lineament (FORCELLA et alii, 1982); the latter is partly influenced by the south-western termination of Engadine Line, a late-alpine sinistral strike-slip fault (TRÜMPY, 1977; SCHMID & FROITZHEIM, 1993). Pianazzola lays on a post-glacial landslide mass (AGOSTONI et alii, 1997), with a volume of approximately 60 × 106 m3. The sliding scar is located close to the lithological boundary between a highly fractured Variscan metagranitemetagranite and an intensely deformed gneisses suite, both belonging to middle Penninic Tambò nappe (MONTRASIO & SCIESA, 1988; MARQUER, 1991). Landslides played and keep on playing an important role in geomorphic processes in the whole Sondrio Province, so that the Chiavenna inhabitants do live on several landslide masses. Starting from Middle Age, the cultivations and the subsequent hydrogeological failure monitoring have been managed by the building up of a stone wall system supported terraces and a drainage canals network (BONARDI & SCARAMELLINI, 2004). Terraced areas allow vine growing in the lower part, up to about 700 m a.s.l., and chesnut (Castanea sativa) in the upper one, up to about 1,100 m a.s.l. The partial re-naturalization of Valchiavenna slopes is the consequence of the territory depopulation during the last decades of the XXth century. The incoming future offers the opportunity of an experimental vineyard «niche« production of a dessert white wine, based on Sauvignon and Kerner wine grapes; the withering and shrinkage technique is the same one used for the well known Valtellina's Sforzato.