HUMIPEDON DYNAMICS IN ALPINE SOILS AFTER A SEVERE WINDSTORM

In October 2018, “Vaia” storm hit the Italian Alps, causing major damage to forests. The resulting changes in microclimate and soil structure are expected to shape the structure of soil communities and the dynamics of humus formation and of soil organic matter (SOM) accumulation. In Val Di Fassa (Trentino-Alto Adige, Italy), 12 sites were identified, uniform in altitude and plant composition, half of which was hit by the storm. Soil samples of 3 conditions were taken: intact forest (IF); under grass in windthrow areas (G); under decaying wood in windthrow areas (W). For each sample, Humus system was identified, soil arthropod community were analysed, and SOM stored in organic (O) and organo- mineral (A) soil horizon was quantified. Regarding Humus, the majority of IF samples express Amphi system (86%). This percentage drops to 50% in windthrow areas, with small differences between G and W, where the other 50% is represented majorly by Mull system. SOM quantification shows a similar pattern, with IF containing a greater quantity of SOM compared with G and W. Considering also soil microarthropods communities’ parameters (abundances, number of taxa, Shannon index, QBS-ar index), FAMD Analysis shows that the IF category is the only cluster that deviates from the others and that there’s no clear differentiation between G and W. Only the structure of the community in W was different from the other categories. In conclusion, in studied forest sites, the passage of Vaia storm produced a shift in the functionality of the humipedon, from a system characterized by a medium speed of SOM turnover (Amphi) to one with a faster turnover of SOM (Mull). The differences are clear between intact forest soils and windthrow soils, but not between conditions in windthrow soils. The small differences observed between G and W suggest that different management of windthrow areas cannot influence humipedon dynamics in these few years after the disturbance. Longer monitoring is needed to help address this question Keywords: Alpine Humus,Soil microarthropods,Windthrow,SOM dynamics