Valutazione della riforestazione spontanea. Un esempio nelle Alpi Retiche italiane

In the Mara valley situated in Rhaetian Alps of Valtellina near Sondrio, where the use of fodder meadows (Arrhenatheretalia) goes back, the extension in % of woods in the years 1935,1975, 1993 was calculated using topographical maps for years 1935 and 1993, and vegetation map for year 1975. In addition a carefully survey of vegetation was made in 1997. Formerly the regarded period, extensively managed pastures of same valley were reforested with Pinus sylvestris a Larix decidua in their parts most degraded and eroded. The area of wood increased (tab. 1) to detriment of anthropogenic vegetation os fodder meadows, matgrass swards(Nnardetalia), arid pastures (Festucetalia vallesiacae). Now secondary successions are under way to re-establishment the high forest whose most developed faces the spruce rules. One surveys three ways starting respectively from a) larch secondary park woodland (tab.2 e tab. 2bis) b) misured meadows or pastures by settlement of borde communities (Rubetum idaei) (tab. 3) c) Calluna health on arid and warm slopes (tab. 4 e tab. 4bis). THese secondary successions draw togheter in very heterogeneous wood ruled by larch and spruce, but very por in Vaccinio-Picetea species. The position of this semi-natural woodland in regard to altitude levels is discussed and one remark that the very hard anthropogenic effects in firsts decades of the Twenty Century, are still recognisable as structural and floristic features. Decrease of pasturing in the Alps causes strong changes to landscape. The authors conclude that these changes could be defined with generic valuations as increasing of wood area, floristic diversity and reinstatement of border communities. These features can be specified locally and valued in regard to new uses of the interesting zones.