Early stages of the serpentine syndrome in the Alps : results from a proglacial area

Glacial retreat since the end of the Little Ice Age (LIA, 190-160 years ago) caused the exposure of “new” surfaces, over which ecosystems and soils develop following different pathways associated to different lithology. The Verra Grande glacier forefield has a serpentinitic lithology, with small gneiss amounts in eastern sectors. We sampled soils and surveyed vegetation in 55 sites, in order to observe the pedogenic trends and the associated plant-soil relationships, and characterize the early stages of serpentine syndrome in subalpine, mid-latitude environments. The soils developed slowly, with only minor organic matter accumulation and acidification, and increase in exchangeable Ni in 190 years. No trends in the Ca/Mg ratio nor in available P were measured. The difference was striking when compared with nearby glacier forefields on gneiss, where podzolization was ongoing in LIA soils. Where minor amounts of gneiss were present, a slightly faster pedogenesis occurred, associated with a stronger nutrient bioaccumulation. As a consequence, the terrain remained almost barren for more than 190 years since moraine deposition on pure serpentinite, while higher P and lower Ni availability were associated with a turnover of 7 plant communities where small quantities of gneiss were present. While on Alpine mature serpentine soils only Ni was associated with vegetation differences, P cannot be excluded from the important factors in early stages of serpentine ecosystem.