Evolution of Forest Humipedon Following a Severe Windstorm in the Italian Alps: A Focus on Organic Horizon Dynamics

This study investigates the effects of the 2018 Vaia windstorm on the evolution of humus profiles in forest soils of the north-eastern Italian Alps five years after the disturbance. The humipedon in five soil conditions was compared: intact forest (IF) and permanent meadow (M) for undisturbed soils, and soil under herbaceous cover (G), under dead wood (W), and bare soil (B) for windthrow-affected areas. No difference in pH and soil organic matter content (SOM) emerged within the same soil horizon between IF and windthrow-affected soils. When compared to IF, however, in G and B, a thinning of all O horizons (OL, OF, and OH) was detected, resulting in SOM loss and an increase in pH in the top 15 cm of the humipedon, conditions approaching the values found in M. Amphi was the most frequently occurring humus system in IF, with a shift towards a Mull system observed in all windthrow-affected soils—a shift more marked in G and B, approaching M conditions, but less marked in W, where the O horizon remained thicker. This study underscores the importance of considering soil heterogeneity and humus dynamics when assessing forest recovery and resilience after a severe disturbance.