Suoli e ambienti del Parco Naturale del Mont Avic (AO) - 2: le foreste

The forests of Mont Avic Natural Park (Ao, Italy) show many peculiarities, due to the ophiolitic substrate, (serpentinite with associated mafic rocks and calcshists) and to the main tree species: subalpine level is dominated by Pinus uncinata, while in the mountainous level there is the northernmost beech forest in the Aosta Valley. The soils show peculiar chemical and physical properties, that are seldom related with vegetation communities. Soils under beech (Luzulo-Fagetum), and on the warm slopes of the mountainous zone under Pinus sylvestris and P. uncinata, are little developed (Regosols, Cambisols, according to WRB 2006), and show some common features: pH<5.5, changeable base saturation, Ca/Mg ratio around 1, high Ni and Cr content (up to 1200 ppm), Moder humus form. On mafic rocks pH values are lower and trace metals content is less than 300 ppm. Vegetation communities are acidophilous (on serpentinite enriched with many Brassicaceae). On the cold slopes of the subalpine level, under P. uncinata forest, podzolization is active on every lithology, but particularly strong on mafic rocks. Some soil properties on serpentinite are: pH<4 in surface horizons, low base status, Ni, Cr content <800 ppm, high metal mobility, Ca/Mg<1; on mafic rocks: pH<4, Ni and Cr content <250 ppm, Ca/Mg >1. Humus form (Mor) and vegetation (Rhodoreto-Vaccinietum) don’t seem to be influenced by parent material, bur Carex fimbriata and many Brassicaceae grow only on serpentinite