High C stocks in Umbrisols in Valgrande National Park (NW Italy)

Valgrande National Park is characterized by a particularly high mean precipitation amount (up to 2500-3000 mm per year), and this factor contributes to the widespread presence of Umbrisols. In order to understand their distribution and pedogenesis, we opened and analyzed 19 soil profiles and observed many non-analyzed minipits under different land uses. The results show that Umbrisols are indeed the most common soil types under most land uses. Cambisols can be observed only in highly disturbed positions, while Umbric Podzols can be found under heath. Commonly, Umbrisols also have a black Sombric Bh horizon below 30 cm of depth. As expected on sialic parent materials under a very wet climate, the soils are extremely acidic and dominated by exchangeable Al. The C stocks are high, with values commonly above 18-20 kg/m2, mainly located in the mineral horizons. There are no differences with land uses: the lowest C stocks were measured in disturbed soil profiles, where erosion or recent deposition made the soil less thick. 1-3 C kg/m2 are stored in organic layers, with the highest values measured in Umbric Podzols under heath. 40-60% of the total C stored in mineral horizons is located under 30 cm of depth, thus measuring its content only in the top 30 cm would lead to a huge underestimation of C stocks.