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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]

Land use composition and patterns influence the hydrological response in mountainous and forest catchments. In plantation forest, management operations (FMO) modify the spatial and temporal dynamics of overland flow processes. However, we found a gap in the literature focussed on modelling hydrological connectivity (HC) in plantation forest under different FMO. In this study, we simulated HC in two steep paired forest subcatchments (K2 and K3, 33.2 ha), composed of Japanese cypress ( Chamaecyparis obtusa Endl.) and Japanese cedar ( Cryptomeria japonica D. Don) plantations (59% of the total area) against a tree thinning intensity of 50% at different time. Additionally, construction of new skidding trails and vegetation recovery was simulated on five thinning-based scenarios that covered a 40-month test period (July 2010 – October 2013). As a future scenario, six check-dams located in the main streams were proposed to reduce sediment and radionuclide delivery. An updated version of Borselli's index of runoff and sediment connectivity was run, using the D-infinity flow accumulation algorithm and exploiting three 0.5-m resolution digital elevation models. On the basis of the pre-FMO scenario, HC increased at catchment scale owing to tree thinning and the new skidding trails. This change was more noticeable within the area affected by the FMO, where HC increased by 11.4% and 10.5% in the cypress and cedar plantations in K2 respectively and by 8.8% in the cedar plantation in K3. At hillslope plot and stream scales, the evolution in the values of HC was less evident, except the increment (by 5.4%) observed in the streams at K2 after the FMO. Progressive vegetation recovery after the FMO triggered a slight reduction of connectivity in all compartments of both subcatchments. Forest roads and especially skidding trails presented the highest values of HC, appearing as the most efficient features connecting the different vegetation patches with the stream network. The spatial and temporal evolution of HC over the five past scenarios correlated well with the observed changes in runoff yield, as well as with the available values of rainfall interception and throughfall before, during, and after the FMO. The simulation of the proposed scenario recommends the construction of check-dams as effective landscape features to somewhat reduce HC and thus to decrease the sediment and radionuclide delivery rates from the two subcatchments. [ABSTRACT FROM AUTHOR]