Abstract
This study examined the changes in rainfall-runoff characteristics in the year prior to and after intensive thinning of 50% in number in a steep headwater catchment, covered with 46-year-old Japanese cedar and cypress in western Japan. The magnitude of event peak flow, event quick flow, event water yield, and event response time did not change after thinning. Because 70% of rainfall events had multiple flow peaks, relationships between each flow peak and the rainfall just prior to that peak were also analyzed. The increases in accumulated quick flow, flow rise and flow drop were significant after thinning. The flow drop following each flow peak increased, and led to a lower initial flow in subsequent peaks, resulting in no increase in peak size. The flow peaks in events with over 30 mm rainfall amount and over 2 mm/h average rainfall intensity showed significant increases in flow peak, flow rise, flow drop, and accumulated quick flow, which suggests that the catchment exhibited more shallow flow paths during large rainfall amounts after thinning. No changes were identified using event-based analysis, but changes in flow peaks were detected, which indicates the importance of examining all flow peaks when investigating rainfall-runoff characteristics of headwater catchments.
Highlights
In Japan, about 68% of the land surface is covered by forests on steep mountains [1]
Thinning of tree numbers by 50% was performed in the Yayama Experimental Catchment (YEC), a steep headwater catchment in
To capture the effects of thinning on rainfall-runoff characteristics more effectively, we examined all the flow peaks for all rainfall events
Summary
In Japan, about 68% of the land surface is covered by forests on steep mountains [1]. Because of the sparse understory vegetation beneath a dense canopy in abandoned plantations, soil erosion and overland flow on hillslopes can occur [4,5,6,7]. As the area of abandoned or non-managed plantation forest increases, thinning to increase tree growth [8]. Has emerged as a forest management tool to prevent environmental problems, such as erosion and floods [3]. After thinning, improved light conditions under the forest canopy can increase the growth of understory vegetation [9]. This growth can improve forest floor conditions by altering infiltration capacities and potential for shallow flow pathways [10]
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