Assessment of topsoil evolution associated with land use change in Val Camonica subalpine grasslands

Alpine pastures and meadows are agroecosystems with biological and landscape importance, protected by the European Union. Grassland areas had a rapid decline in the last decades due to changes in management and/or abandonment of traditional mountain farming in the Alps. The aim of our study is the characterization of the relationship between historical and present-day subalpine grassland management, their plant diversity, soil properties and humus forms. Humus forms are important indicators of biological functioning of soils and of organic matter degradation pathways, easily affected by land use change. We chose two areas in Alta Valle Camonica (Rhaetian Alps, Lombardy), between 1800-2000 m a.s.l., on sialic glacial till, characterized by strong land use changes, as visible in historical aerial photographs. Since the 70s, large herbaceous surfaces are being colonized by subalpine heath and forests, because of a decreased and more localized grazing pressure. We selected 21 sites across six dynamic phases from grazed grassland to forest, in which we performed phytosociological surveys (10x10 m) according to the Braun-Blanquet method, a soil profile and a characterization of topsoil and organic horizons to detect humus forms and properties. Standard physico/chemical soil properties were analyzed in the lab. The widespread decrease in grazing intensity led to an expansion of less palatable grasses (e.g., Nardus stricta L.), shrubs and trees, and thus changes in plant diversity and vegetation structure. Soils are mostly Entic/Umbric Podzols, Histosols in bogs. Humus forms are more varied: we observed Rhizo humus systems where grass roots were a main source of organic matter in soils. Mull and Amphi are the main forms in grazed areas, Dysmoders and Hemimoders in abandoned soils colonized by trees, Tangels in bogs; no Mors have been detected. Thus, humus forms and biological activity/organic matter degradation pathways can describe the gradients in land use change. Some more differences might be observed in the experimental phases, with microbial analysis and topsoil thin section observations.