Forest Management for the Flood Mitigation Function of Forests

Paired catchment experiments is the method that estimates the change of runoff due to forest change by comparisons between runoff data from two or more adjacent catchments and evaluations the change of their relative relations between two periods when forest changes in catchments. The increase in volume of maximum daily runoff due to forest degradation was estimated in three treatment catchments in Japan using paired catchment experiments. In one catchment, slope failure occurred and 20% of the catchment area became bare, after which maximum daily runoff increased by approximately 1.1-fold. In the two other catchments, slope failure did not occur, while maximum daily runoff increased by only 6–8 mm day−1. This increase was irrespective of the rainfall volume. slope failure and the transition to bare land were identified as causes of the degradation of the flood mitigation function. The causes of slope failure were identified as inadequate forest management, such as clear-cutting in areas with high slope failure risk, simultaneous clear-cutting throughout a catchment, and delayed replanting after clear-cutting. Therefore, forest management strategies for the flood mitigation function of forests could include the avoidance of logging in locations with a high risk of slope failure, limits concerning the amount of logging, and prompt replanting after logging.