Abstract
Wind is one of the major forest disturbance agents in the Alps and due to the ongoing climate change could assume a greater relevance in the future management of the Alpine forest populations. While the recent and widespread windthrow events in the Alpine area seems to confirm this hypothesis, still little is known about how alternative post-event treatment scenarios affect the hydrological and erosional processes of windthrown hillslopes. This study aims to reveal the influence that the most common silvicultural treatments applied after windthrow have on the hydrological and erosive response. Therefore, surface runoff and soil losses from four experimental field plots were examinated andcompared after non-intervention (NI), and after salvage logging and natural regeneration (CN) or planted regeneration (CP). The studied plots refer to these three treatment options after two major windstorm events (2003 and 2018) in two successive growing seasons (2021-2022).
The results obtained so far indicate a statistically significant variability in sediment concentration between plots (0–1606 g L-1), although event runoff (0.1–3.9 mm), runoff coefficient (0.004–0.105), and sediment yield (0–9517 kg ha-1) do not show significant differences among plots and years. No Intervention plot damaged in 2018 (NI2018) showed a slightly but significantly longer time to runoff compared to deadwood-cleared (CN2003). This effect is probably attributable to a higher surface roughness coefficient. Soil losses from artificially regenerated plots (CP2003 and CP2018) responded more strongly than those from naturally regenerated plots (NI2018 and CN2003) during rainfall events with larger cumulative depths. This effect may be partially explained by initial soil disturbances associated with pre-planting site preparation. The older plantation (CP2003) generally present higher hydrological and erosional susceptibility compared to the younger plantation (CP2018), likely owing to an advanced successional stage with a relatively larger throughfall erosive power and a higher biomass flow potential. Our findings—though still based on limited data coverage—highlight the legacy effects of commonly practiced post-windthrow silvicultural treatments, which persistently alter hydrological and erosional responses even 3–19 years after the application. Hydrological and erosive consequences of such interventions should therefore be taken into account in the decision-making process on interventions to be applied on forest windthrow.