Search

We examined changes in catchment‐scale annual and seasonal evapotranspiration after 50% strip thinning, using runoff data from headwater catchments. The short‐term water balance (STWB) method between periods from 8 to 100 days was applied to the treated (KT) and control (KC) catchments. The estimated evapotranspiration during the pre‐ and post‐thinning periods were 840 and 910 and 780 and 860 mm/year in the catchments KT and KC, respectively. According to a paired catchment analysis of estimated evapotranspiration, monthly evapotranspiration increased from 3 to 20 mm from June to December, while it decreased from 7 to 31 mm from January to May. The estimated annual and monthly evapotranspiration was compatible with the values monitored in the plot‐scale interception, canopy transpiration, and ground surface evapotranspiration. Our findings showed that the decreases in evapotranspiration due to 50% thinning were similar or different in different methods of measurement when compared with thinning in the other catchments around the world. The STWB model can evaluate the effects of timber harvesting on changes in evapotranspiration (ET), including the reproduction of seasonal patterns of ET. [ABSTRACT FROM AUTHOR]

We evaluated the effects of 50% strip thinning on peak flow responses in 17-ha and 9-ha nested catchments. We observed 117 storm events from April 2010 to December 2013, including 32 events in the pre-thinning period, 15 events during the thinning operation, and 70 events in the post-thinning period. Paired-catchment analysis with multiple pairs of nested gauging stations revealed that changes in peak flow responses varied depending on the location of the nested observation stations. Increases in peak flow during the operation period were significant in gauging stations located at the outlet and the middle of a catchment. Increases in peak flow during the post-treatment period became significant in all nested catchments, but not in the catchment outlet. Rates of increase in peak flow ranged from 17.7% to 44.4%, which is within the range of previous studies. Different responses for changes in peak flow among nested pairs were associated with changes in internal hydrological flow pathways due to removal of timber and hydrological connectivity via overland flow generated by newly installed and reactivated skid trails. Our findings suggest that the effects of timber harvesting on peak flow are scale-dependent with respect to drainage areas, hydrological links, and management practices. Selection of gauging locations and process-based observations within catchments are essential for testing hypotheses related to the effects of timber harvesting with robust hydrological monitoring. [ABSTRACT FROM AUTHOR]

Summary: We examined the effect of forest thinning on runoff generation at plot and catchment scales in headwater basins draining a Japanese cypress (Chamaecyparis obtusa) forest. We removed 58.3% of the stems (corresponding to 43.2% of the basal area) in the treated headwater basin (catchment M5), and left the control catchment (M4) untreated. In both catchments, we monitored overland flow from hillslope plots and stream runoff from catchments at basin outlets over a 2-year pre-thinning period and a 2-year post-thinning period. Paired catchment analysis revealed that annual catchment runoff increased 240.7mm after thinning. Delayed runoff increased significantly, while quick runoff followed similar patterns in the pre- and post-thinning periods. Flow duration in the ephemeral channel in catchment M5 increased from 56.9% in the pre-thinning period to 73.3% in the post-thinning period. Despite the changes in hydrological responses at the catchment scale, increases in overland flow were not significant. The increased availability of water in the soil matrix, caused by decreased interception loss and evapotranspiration, increased base flow after thinning. Based on the summarized data of previous studies together with this study, the effects of forest thinning on increases in runoff were less than partial harvesting in which the managed areas were concentrated within a watershed. We demonstrated that the effect of forest thinning was strongly scale dependent, an important finding for optimizing water and forest management in forested watersheds. [Copyright &y& Elsevier]