Early stages of soil development on serpentinite: the proglacial area of the Verra Grande Glacier, Western Italian Alps

Climate change is driving strong variations in mountain habitats, such as glacier retreat, which is releasing large surfaces soon colonized by vegetation and attacked by weathering and pedogenesis. Many proglacial soil chronosequences have been studied in different parts of the world, but no study is available on early soil development and pedogenesis on serpentinite. We analysed the development of the main chemical (pH, organic matter, nutrients and exchangeable cations) and morphological properties in three soil chronosequences in the Verra Grande Glacier forefield (Italian side of the Monte Rosa Group, Western Alps), characterized by slightly different parent materials (pure serpentinite or serpentinite with small gneiss inclusions) and topography (steep lateral moraines or flat basal till). Organic matter accumulation, acidification and base and metal leaching are the most important pedogenetic processes active during early stages of soil formation on serpentinite in the upper subalpine altitudinal belt. These processes are associated with minor changes in color and structure showing weak mineral weathering. Biocycling of nutrients is limited on pure serpentinite because of weak primary productivity of the plant community. Pedogenesis is quite slow throughout the forefield, and it is slowest on pure serpentinite. On flat surfaces, where slow erosion permits a fast colonization by Ericaceae, the podzolization process begins after few centuries since moraine deposition, while on steep slopes more time is required. Pedogenesis on serpentinite is extremely slow. The fast colonization by grassland species increases the speed of pedogenetic trends where serpentinitic till is enriched by small quantities of P-rich gneiss. The encroachment of forest-shrub species increases the speed of pedogenetic trends thanks to a strong nutrient biocycling.