Effects of Forest Operations on Runoff and Sediment Variations in Catchments Under Intense Forest Activity and Climate Stress in the South-Central Chile

Forestry operations and climate variability affect hydrologic response and sediment transport. Management of forested catchments under intense forestry activity in areas under climatic stress is critical. This study analyzes the impact of forest operations (thinning and clearcutting) on runoff (Q) and suspended sediment loads (SSL) in three small catchments (named N02, N03 and N04, respectively) in south-central Chile, where rainfall has decreased by 20% since 2010. Using modified double mass curves and piecewise regression, we separated the effects of forest practices and climate. Thinning in N02 initially reduced Q and SSL, with stable Q overtime, while final harvest in N03 and N04 increased Q, although less than expected. SSL surged post-harvest: 3.6 times in N03 and 1.8 times in N04, potentially linked to hillslope instability. Major SSL events contributed over 55% of post-harvest sediment yield in both catchments, with maximum yields reaching 7.2 tons ha−1 yr−1 in N03 and 4.1 tons ha−1 yr−1 in N04. SSL recovered to pre-harvest levels by the third year, except during a rainy year. Management practices likely contributed to lower SSL and faster recovery. These findings improve our understanding of catchment responses to forest practices and climate change, aiding sustainable forest and water resource management.