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This study investigated the impact of thinning and felled logs (random- and contour-felled logs) on overland flow, soil erosion, and litter erosion in a Japanese cypress forest plantation (2400 tree ha−1) with low ground cover, from 2018 to 2023 in central Japan. Monthly measurements of overland flow and soil and litter erosion were carried out using small-sized traps across three plots (two treatments and one control). In early 2020, a 40% thinning (tree ha−1) was conducted in the two treatment plots. Overland flow increased in the plot with random-felled logs during the first year post-thinning (from 139.1 to 422.0 L m−1), while it remained stable in the plot with contour-felled logs (from 341.8 to 337.1 L m−1). A paired-plot analysis showed no change in overland flow in the contour-felled logs plot compared to the control plot from the pre- to post-thinning periods (pre-thinning Y = 0.41X − 0.69, post-thinning Y = 0.5X + 5.46, ANCOVA: p > 0.05). However, exposure to direct rainfall on uncovered ground areas post-thinning led to increased soil and litter erosion in both treatment plots. These findings suggest that thinning combined with contour-felled logs effectively stabilizes overland flow. Therefore, thinning with contour-felled logs can be considered a viable method for mitigating overland flow in monoculture plantations with low ground cover. [ABSTRACT FROM AUTHOR]

Contour felling is a restoration method used to decrease overland flow (OF) and soil erosion in the world. However, the impact of thinning and the placement of felled logs on OF remains inconclusive. Low ground cover and soil permeability promote OF in Chamaecyparis obtusa (Siebold et Zucc.) Endl plantations, making thinning a method for reducing runoff. We examined the relationship between OF and ground cover in a C. obtusa plantation in Japan. Event-based runoff was monitored in three plots from 2016 to 2021, with 40% thinning conducted in 2019. In plot T1, logs were randomly scattered, and, in T2, logs followed contour lines, while control plots stayed the same. After thinning, both treatment plots showed lower OF than the control plot. The ANCOVA test shows a significant slope reduction in treatment plots compared to the control plot from pre-thinning to post-thinning (T1: 0.67 to 0.26, T2: 0.66 to 0.12, p < 0.001, Tukey HSD test). However, in plot T2, OF remained stable for two years post-thinning, affirming the enduring effectiveness of contour-aligned log placement. This study backs the notion that aligning fallen logs with contour lines boosts long-term OF infiltration, supporting sustainable forest and soil management. [ABSTRACT FROM AUTHOR]

In order to overview the impact of climate change on runoff from forested catchments over Asian countries, we collected water balance data from fifteen long-term catchment monitoring stations (total monitoring period 1975–2018, not continuous), spanning from Sabah, Malaysia (our southernmost site), to Hokkaido, Japan (our northernmost site). We then employed an elasticity analysis to the dataset to examine how the annual runoff from each catchment responded to inter-annual fluctuations in annual rainfall and annual mean air temperature. As a result, we found that (1) the annual runoff was sensitive to annual rainfall for all the catchments examined. In addition, (2) the annual runoff from seven of the fifteen catchments was sensitive to inter-annual changes in the mean air temperature, which was likely due to changes in forest evapotranspiration. Three catchments, however, exhibited an increased runoff in a hot year. Finally, (3) the annual rainfall from the previous year (carry-over soil moisture) was important in explaining the variation in annual runoff in two tropical montane forest catchments. This study may serve as one of the pilot studies toward a comprehensive understanding of the climate elasticity of runoff in countries over Asia, because the examined catchments are unevenly and sparsely distributed over the area. [ABSTRACT FROM AUTHOR]

While timber harvesting has plateaued, repeat-logging and conversion into plantations (especially oil palm) are still active in the tropics. The associated hydrological impacts especially pertaining to enhanced runoff, flood, and erosion have been well-studied, but little attention has been given to water resource availability in the humid tropics. In the light of the increasing climate extremes, this paper compared baseflow values and baseflow recession constants (K) between headwater catchments of five differing land-uses in Sabah, Malaysian Borneo, namely primary forest (PF), old growth/virgin jungle reserve (VJR), twice-logged forest with 22 years regeneration (LF2), multiple-logged forest with 8 years regeneration (LF3), and oil palm plantation (OP). Hydrological and meteorological sensors and dataloggers were established in each catchment. Daily discharge was used for computing K via four estimation methods. Catchment ranks in terms of decreasing K were VJR (0.97841), LF3 (0.96692), LF2 (0.90347), PF (0.83886), and OP (0.86756). Catchment ranks in terms of decreasing annual baseflow were PF (1877 mm), LF3 (1265 mm), LF2 (812 mm), VJR (753 mm), and OP (367 mm), corresponding to 68%, 55%, 51%, 42%, and 38% of annual streamflow, respectively. Despite the low K, PF had the highest baseflow magnitude. OP had the fastest baseflow recession and lowest baseflow magnitude. Baseflow persistence decreased with increasing degree of disturbance. K showed strong association to catchment stem density instead of basal area. For dynamic catchments in this study, the Kb3 estimator is recommended based on its lowest combination of coefficient of variation (CoV) and root mean squared error (RMSE) of prediction. For wetter catchments with even shorter recession events, the Kb4 estimator may be considered. Regarding climate change, logging and oil palm agriculture should only be conducted after considering water resource availability. Forests (even degraded ones) should be conserved as much as possible in the headwaters for sustainable water resource. [ABSTRACT FROM AUTHOR]

There have been conflicting findings on hydrological dynamics in tropical montane cloud forests (TMCFs)—attributed to differences in climate, altitude, topography, and vegetation. We contribute another observation-based comparison between a TMCF (8.53 ha; 1906 m.a.s.l.) and a tropical lowland rainforest (TLRF) (5.33 ha; 484 m.a.s.l.) catchment in equatorial Sabah, Malaysian Borneo. In each catchment, a 90° v-notch weir was established at the stream's outlet and instrumented with a water-level datalogger that records data at 10-min intervals (converted to discharge). A nearby meteorological station records rainfall at the same 10-min intervals via a tipping bucket rain gauge connected to a datalogger. Over five years, 91 and 73 storm hydrographs from a TMCF and a TLRF, respectively, were extracted and compared. Various hydrograph metrices relating to discharge and flashiness were compared between the TMCF and TLRF while controlling for event rainfall, rainfall intensity, and antecedent moisture. Compared to the TLRF, storm-event runoff in the TMCF was up to 169% higher, reflecting the saturated conditions and tendency for direct runoff. Instantaneous peak discharge was also higher (up to 6.6x higher) in the TMCF. However, despite high moisture and steep topography, stream responsiveness towards rainfall input was lower in the TMCF, which we hypothesise was due to its wide and short catchment dimensions. Baseflow was significantly correlated with API20, API10, and API7. Overall, we found that the TMCF had higher runoff, but higher moisture condition alone may not be sufficient to govern flashiness. [ABSTRACT FROM AUTHOR]

Many studies have focused on soil erosion in unmanaged Japanese cypress plantations because the sparse understory vegetation and litter covering the forest ground enhance soil erosion. In this study, soil erosion, litter, and overland flow measurements were conducted over 14 months to identify the spatio-temporal variation and examine the optimal sample size. Fifteen traps (each 0.25 m wide) were installed in line along the bottom of a 15-m-wide slope. Soil erosion and overland flow had large spatial variations as compared to litter. The temporal coefficient of variation of soil erosion and overland flow was highest during dry seasons, while smaller during wet seasons. The random sampling analysis showed that the rate of decrease in spatio-temporal variation became moderate as the sample size increased beyond six. This result indicated that the optimal sample size was five, the total width of which was equivalent to about 8% of the monitored slope width. [ABSTRACT FROM AUTHOR]

Freshwaters provide valuable habitat and important ecosystem services but are threatened worldwide by habitat loss and degradation. In Southeast Asia, rainforest streams are particularly threatened by logging and conversion to oil palm, but we lack information on the impacts of this on freshwater environmental conditions, and the relative importance of catchment versus riparian-scale disturbance. We studied 16 streams in Sabah, Borneo, including old-growth forest, logged forest, and oil palm sites. We assessed forest quality in riparian zones and across the whole catchment and compared it with stream environmental conditions including water quality, structural complexity, and organic inputs. We found that streams with the highest riparian forest quality were nearly 4 °C cooler, over 20 cm deeper, had over 40% less sand, greater canopy cover, more stored leaf litter, and wider channels than oil palm streams with the lowest riparian forest quality. Other variables were significantly related to catchment-scale forest quality, with streams in the highest quality forest catchments having 40% more bedrock and 20 times more dead wood, along with higher phosphorus, and lower nitrate-N levels compared to streams with the lowest catchment-scale forest quality. Although riparian buffer strips went some way to protecting waterways, they did not maintain fully forest-like stream conditions. In addition, logged forest streams still showed signs of disturbance 10-15 years after selective logging. Our results suggest that maintenance and restoration of buffer strips can help to protect healthy freshwater ecosystems but logging practices and catchment-scale forest management also need to be considered. [ABSTRACT FROM AUTHOR]

Relatively minimal attention has been given to the hydrology of natural broadleaf forests compared to conifer plantations in Japan. We investigated the impacts of ground litter removal and forest clearing on surface runoff using the paired runoff plot approach. Plot A (7.4 m2) was maintained as a control while plot B (8.1 m2) was manipulated. Surface runoff was measured by a tipping-bucket recorder, and rainfall by a tipping-bucket rain gauge. From May 2016 to July 2019, 20, 54, and 42 runoff events were recorded in the no-treatment (NT), litter removed before clearcutting (LRBC), and after clearcutting (AC) phases, respectively. Surface runoff increased 4× when moving from the NT to LRBC phase, and 4.4× when moving from the LRBC to AC phase. Antecedent precipitation index (API11) had a significant influence on surface runoff in the LRBC phase but not in the NT and AC phases. Surface runoff in the AC phase was high regardless of API11. The rainfall required for initiating surface runoff is 38% and 56% less when moving from the NT to LRBC, and LRBC to AC phases, respectively. Ground litter and canopy function to reduce surface runoff in regenerated broadleaf forests. [ABSTRACT FROM AUTHOR]

Understanding baseline runoff characteristics is critical in any water balance study whether single- or multiple-catchment. As a product of interaction between many area-specific factors (scale, climate, geology, vegetation, land-use history), each catchment can only be well-understood through a reasonable period of baseline observation. In temperate regions, processes are complicated by a range of meteorological factors and plant phenological periods (growth and dormant) as well as the way vegetation reacts to these factors resulting in varying water uptake from soils. In the Inuyama Research Forest of the Ecohydrology Research Institute in Aichi prefecture, central Japan, streams in two small headwater catchments (cypress plantation, 2.2 ha; secondary mixed-broadleaf, 2.1 ha) were instrumented with 90° v-notch weirs and automatic data loggers that recorded water level at 5-minute intervals. These data were then converted to discharge via calibration. A weather station was also set up in the area to record rainfall and other meteorological data. After quality control and data filtering, 1,398 daily runoff and rainfall over five years (April 2013-April 2018) were computed and analysed. Data were separated according to plant phenology (growth period from 1st May to 31st October; dormant period from 1st November to 30th April) and explored via runoff coefficients (C) and rainfall-runoff regressions in two ways:- (i) growth vs. dormant periods within individual catchments (cypress and broadleaf); (ii) cypress vs. broadleaf forests within each phenological period (growth and dormant). C-values in the growth and dormant periods are 0.534 and 0.521 for cypress; and 0.506 and 0.525 for broadleaf respectively. Within individual catchments, the cypress catchment has a 2.5% higher C-value in the growth period (0.534) compared to in the dormant period (0.521) whilst the broadleaf catchment shows a 3.6% reduction instead (0.506 in growth; 0.525 in dormant). This suggests that during the warm and humid growth period, the increased water uptake by cypress trees does not offset the influence exerted by higher rainfall. However, the slopes of rainfall-runoff relationship are higher during the growth period in both catchments. For comparison between the two catchments within the same phenological period, the 5% lower C-value in broadleaf (0.506) compared to cypress (0.534) reflects higher water use by broadleaf trees during the growth season whereas similar values (0.521 in cypress, 0.525 in broadleaf) during the dormant season indicate continual rainfall interception by cypress even after leaf abscission in the broadleaf catchment. This is further supported by the higher slope of rainfall-runoff relationship in the broadleaf catchment during the dormant period. This study has shown that rainfall-runoff relationships in this area differ according to vegetation type and phenological periods. Hence, forthcoming catchment hydrological studies should be designed to control for these effects. [ABSTRACT FROM AUTHOR]

It is well known that a logging/harvesting practice in a forested catchment induces evapotranspiration (ET) decline and a subsequent runoff increase. In addition, most previous paired-catchment studies have revealed that, after re-planting the same tree species in the logged catchment, the post-logging runoff increase gradually diminished and returned to pre-logging level within short time period (typically 5-15 years), due to increasing water use by the planted trees with their growths. However, there is relatively little information on how longer-term catchment water balance changes with maturity of trees in the catchment. Marc and Robinson (2007) is one the few studies, in which, based on long-term catchment water balance data in UK, they reported that ET reduced by 140 mm per year in spruce/pine catchments with increasing forest ages. In order to fill the knowledge gap further, we revisited long-term water balance data for a Japanese catchment in which the soil and vegetation had been disturbed due to forest overuse, until its establishment in 1929 by University of Tokyo. Initially, the catchment was covered by young pines with scattered denuded ridges. After the catchment establishment, the poor vegetation had gradually been matured and the scattered denuded ridges had been decreased particularly after 1960s. Because the matured pine trees in the catchment had been largely declined due to an epidemic (pine wilt disease) during 1980s, we examined annual loss of the catchment from 1930s to 1970s. The result showed that the annual loss decreased with the decades, i.e., pine maturing, by about 100-150 mm per year. A further event-basis water balance analysis (Linsley et al. 1982) showed that the decline in the annual loss was caused by ET decline in the mid-growing season while ET in the dormant season exhibited almost no change throughout decades. Though, in order to draw a solid conclusion, a further investigation is still needed considering fluctuations in meteorological factors (such as air temperature) controlling ET, we currently attribute the ET decline in the mid-growing season to age-related transpiration decline, as was found for maritime pine stands in France (Delzon and Loustau 2005), because canopy interception would be augmented in later decades due to larger above-ground biomass and leave amount. [ABSTRACT FROM AUTHOR]