Legacy effects of post-storm silvicultural treatments on plot-scale soil erosion in a subalpine headwater catchment of the Italian Alps

Wind-disturbed mountain forests are often subject to artificial deadwood extraction and tree planting to accelerate the recovery of timber resources. However, little is known about to what degree and extent those post-storm silvicultural treatments modify the surface processes of wind-affected hillslopes. This study aims to understand how post-storm silvicultural treatments affect soil erosion from wind-disturbed mountain forests by coupling monitoring and modeling approaches. We continuously collected and measured soil losses from four 4.5-m-wide and 6.0-m-long bounded field plots located on wind-disturbed hillslopes with a slope angle of 45 % in a subalpine headwater of the Italian Alps during the vegetation periods from 2021 to 2023. The dominant ground cover of four plots resulting from altered post-storm interventions is characterized by residual deadwood, native herbs, 20-year-old plantation, and 5-year-old plantation, respectively. During 75 analyzed storm events, average soil loss from the native herbs-covered plot (2.4 t ha-1; SD: ±3.5 t ha-1) was the smallest, followed by plots covered with residual deadwood (mean±SD: 3.1±2.9 t ha-1), 20-year-old plantation (mean±SD: 3.5±5.2 t ha-1), and the 5-year-old plantation (mean±SD: 4.5±4.2 t ha-1). Moreover, linear regression models (p-value < 0.001) indicated that two plantation plots potentially yield 2-fold sediment of naturally regenerating deadwood and herbs-covered plots as storm rainfall depth increases. Our three-year field observations highlight the persistent impact of post-storm forest management activities in accelerating soil erosion potentially even 20 years after their implementation. In the next step, the Water Erosion Prediction Project (WEPP) model will be used to further investigate the effect of human treatments on hydrology and sediment transport in storm-affected mountain areas.