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This study investigated the difference in stand transpiration ( E) between upper (UP) and lower (LP) slope plots of a Japanese cypress ( Chamaecyparis obtusa) watershed to obtain catchment-scale E estimates. Sap flux-based stand-scale E estimates were conducted on the UP and LP, which had contrasting stand structures (diameter at breast height and tree height) despite being the same age. The plant area index was similar in the UP and LP, while the total sapwood area ( AS_stand) and the mean sap flux density ( JS) in the UP were 23% and ~30% lower, respectively, than those of the LP. Stand-scale E is the product of the AS_stand and JS in a stand. As a result, E in the UP was ~50% lower than that in the LP. This ratio was relatively constant throughout the year, which was supported by a similar decline in E, which resulted from soil water decline in the UP and LP. Canopy conductance ( GC) in the UP was ~50% smaller than that of the LP. In contrast to previous studies that showed a consistent JS along a slope, the differences in E between the UP and LP were caused by differences in AS_stand and JS, probably because the UP exhibited a lower GC per unit leaf area than the LP. Additionally, evapotranspiration ( ET), the sum of sap flux-scaled E plus rainfall interception, was 8-14% lower than the catchment water balance ET (precipitation minus runoff), which suggests the feasibility of calculating sap flux-scaled E for the two slope positions. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Thinning affects ecohydrological processes under different biophysical conditions, silvicultural systems, and time scales. • Throughfall, net precipitation, soil moisture and tree-level water use increase after thinning by 1.19, 1.14 and 1.56 relative to the control, respectively. • Stemflow and stand transpiration decrease after thinning by 0.42 and 0.6 relative to the control, respectively. • Thinning enhances runoff and groundwater recharge and mitigates the effects of drought through increasing Water Use Efficiency. • Thinning intensity of about 50% of the stand density is determined as the threshold at or over which hydrological processes are significantly affected. • The duration of thinning effect can be set between 2.6 and 4.3 (throughfall) and 3.1–8.6 years (soil moisture and transpiration). Forest thinning can significantly affect hydrological processes. However, these effects largely vary with forest types, climate, thinning intensity, and hydrological variables of interest. Understanding these effects and their variations can significantly support thinning treatments' design and selection to ensure desired hydrological benefits. In this global-level review paper, we report the first comprehensive meta-analysis on the effects of thinning on major hydrological processes with an emphasis on rainfall partitioning, soil moisture and evapotranspiration processes. The synthesized and reviewed studies encompass different biophysical conditions (climate and forest ecosystems), silvicultural systems, and time scales (from weeks to decades) across continents. The results showed a significant increase in net precipitation, soil moisture and tree-level water use after thinning (the effect sizes are 1.19, 1.14 and 1.56 relative to the value of the control, respectively), while decreases in stemflow and transpiration (the effect sizes of 0.42 and 0.6 relative to the value of the control, respectively). Thinning intensity of about 50% of the stand density is determined as the threshold at or over which hydrological processes are significantly affected. The duration of thinning effect can be set between 2.6 and 4.3 (throughfall) and 3.1–8.6 years (soil moisture and transpiration), asking for repeated thinning in order to effectively sustain these effects. These global averages can serve as benchmarks for assessment and comparisons, but the effects of thinning depend on local biophysical conditions and thinning treatments. The literature review on the rest of the studied hydrological variables suggests that thinning generally enhance runoff to increase water yield and groundwater recharge. Thinning can also have a positive or limited role in water use efficiency (WUE), but it mitigates the effects of drought through increasing WUE. Moderate adverse effects on water quality can be prevented by adequate forest managements to prevent soil degradation. Nevertheless, more researches at relatively less studied regions are needed to support a more robust analysis of these reviewed hydrological variables. The management implications of the synthesized and reviewed results are suggested and discussed within the context of climate change. [ABSTRACT FROM AUTHOR]

Forest management (thinning and clearcutting) can reduce evapotranspiration and increase catchment runoff. By summarizing data on the increase in annual runoff (ΔQ) due to forest management at various sites and analysing data using linear regression, traditional studies have reported large unexplained variability among data for different sites. To improve the predictability of ΔQ, it might be useful to model ΔQ for specific species and regions while considering underlying processes. This study performed such modelling for Japanese cedar and cypress plantations in Japan. Model 1 predicts ΔQ assuming that ΔQ equals the decrease in canopy interception loss (ΔEi), which was further modelled by stem density using 46 data for interception loss. Model 2 predicts the potential maximum of ΔQ (ΔQmax) assuming that ΔQmax equals the sum of ΔEi and the decrease in canopy transpiration (ΔEt). Here, ΔEt was calculated using a model developed in our previous study. ΔQ predicted using Model 1 approximated ΔQ observed for seven catchments, and the errors in prediction were less than those derived from traditional linear-regression analysis. ΔQmax predicted using Model 2 was greater than the observed ΔQ for all catchments. Thus, Models 1 and 2 would be respectively useful in assessing the effectiveness and limitations of managing Japanese cedar and cypress plantations to secure water resources, which have been controversial in Japan. Furthermore, the concept of the models gives implications for studies on other species and regions, because the models have demonstrated how to improve predictability of ΔQ considering underlying processes with the input of commonly available data. [ABSTRACT FROM AUTHOR]

The large-scale expansion of Moso bamboo forests in Japan raises concerns about how vegetation will affect the hydrological cycle and local water resources. However, information on transpiration (E) is limited to study on a single bamboo stand with low culm density (4 000 ha-1). The present study conducted a year-round measurement of E in a high-density (11 000 ha-1) stand using sap-flow measurements, and additional measurements were made during summer in the previously studied low-density stand and a neighbouring Japanese cedar stand for comparison. Annual E of the high-density stand was estimated at 455 mm. Although the value was greater than those reported for neighbouring coniferous forests (250-370 mm), it was lower than previous measurements made in the low-density stand (567 mm). The daytime sap flux density of the high-density stand was generally less than half that in the low-density stand, resulting in similar daily maximum E values in those stands. In addition, E typically peaked before midday in the high-density stand followed by a rapid decline; the midday suppression of E led to decreased total E in the stand. Based on present and previous measurements of E, combined with the lower rainfall interception (I) reported for bamboo stands, water loss through evapotranspiration would be comparable between bamboo and coniferous forests. Present results also suggest that the E of bamboo stands does not have strong positive relationships with stand structural parameters (e.g., culm density and sapwood area) but possibly depends more on the sites' microenvironments (e.g., solar radiation). [ABSTRACT FROM AUTHOR]

ABSTRACT We investigated the contribution of three evapotranspiration (ET) components including canopy interception ( Ei), tree transpiration ( Et) and forest floor evaporation ( Ef) and identified the sources depth of evaporated water in a Japanese cypress stand. Monitoring primarily focused on the growing season of July-October 2011. In a 12 × 13 m plot with 28 trees with a DBH of 19.1 ± 3.9 cm, Ei was calculated as the difference between precipitation on an open field and precipitation under a canopy as the sum of throughfall and stemflow, and Et was measured using the Granier method. Ef was measured by weighing lysimeters. Total ET during the monitoring period was 446.3 mm, accounting for 47.5% of the total precipitation of 938.8 mm. Ei was the dominant evaporation flux and accounted for 53.6% of ET or 25.5% of rainfall, followed by Et with 33.7% of ET or 16.0% of rainfall. The average Et was 1.5 ± 0.6 mm d−1. It was well correlated with soil moisture at a depth of 5-15 cm, which reflected the forest properties, i.e. tree roots were exposed on the forest floor. Ef accounted for 12.7% of ET or 6.0% of rainfall with a daily mean of 0.55 ± 0.26 mm d−1, and was best correlated with soil moisture in the upper 5 cm of soil. These results can improve the understanding of water budget in forested watershed and also be used to build and validate hydrologic models for water resource managements. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In recent years, Moso bamboo ( Phyllostachys pubescens) forests have rapidly expanded in Japan by replacing surrounding coniferous and/or broadleaved forests. To evaluate the change in water yield from forested areas because of this replacement, it is necessary to examine evapotranspiration for Moso bamboo forests. However, canopy interception loss, one of the major components of evapotranspiration in forested areas, has been observed in only two Moso bamboo forests in Japan with relatively high stem density (~7000 stems/ha). There are, in fact, many Moso bamboo forests with much lower stem density. Thus, we made precipitation ( Pr), throughfall ( Tf) and stemflow ( Sf) observations for 1 year in a Moso bamboo forest with stem density of 3611 stems/ha and quantified canopy interception loss ( Ic). Pr and Ic for the experimental period were 1636 and 166 mm, respectively, and Ic/ Pr was 10%. The value was approximately the same as values for the other two Moso bamboo forests and lower than values for coniferous and broadleaved forests. On the other hand, Tf/ Pr and Sf/ Pr for our forest (86% and 4%, respectively) were approximately 10% of Pr larger and smaller than values for the other two Moso bamboo forests. These results suggest that the difference in stem density greatly affects precipitation partitioning (i.e. Tf/ Pr and Sf/ Pr) but does not greatly change Ic/ Pr. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In a deciduous larch forest in eastern Siberia, the mean and standard deviation of the total evapotranspiration ( E) during May to September (day of year (DOY) = 121-274) for 2003-2006 were 181.5 and 26.4 mm, respectively. The interannual variation (IAV) in the total E was caused by the IAV in E for the canopy-foliated period (DOY = 164-253), not by the IAV in the dates of leaf expansion and leaf fall. For the years with higher total E, E in the canopy-foliated period was consistently higher, which corresponded to the higher soil water content in these years. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

According to widely held belief, annual evapotranspiration (ET) for broadleaf forests is less than that for coniferous forests, resulting in higher annual runoff for broadleaf forests. We processed 82 catchment runoff and 126 interception loss data from temperate regions and found that although the belief is valid under conditions of broadleaf deciduous forests and high winter precipitation (e.g. the United States), it is invalid under conditions of broadleaf evergreen forests (e.g. New Zealand) or low winter precipitation (e.g. Japan). Thus, forest management policies based on this belief should be reconsidered on the basis of our results for regions with broadleaf evergreen forests or low winter precipitation. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article looks at a model that estimates monthly forest evapotranspiration (E) from monthly temperature in Japan. It mentions that the model's accuracy was tested using monthly E data derived using micrometeorological methods and short-term water balance for 15 Japan forest sites. It notes that the model overestimated monthly E, and could only be reduced by considering the effect of precipitation of E.

Abstract: This study examined the change of water yield when a broad-leaved forest is converted to a coniferous plantation forest after clear-cutting in northern Japan where monthly precipitation is evenly distributed. Annual water yield after clear-cut was greater than observed in a broad-leaved forest and then decreased with the growth of a coniferous plantation forest. This reduction ceased after 30 years from the planting of coniferous seedlings. Water yield of a coniferous forest at this stage was smaller than observed in a broad-leaved forest. Results from monthly water yield examinations suggested that the difference in annual water yield was primarily caused by the difference in winter interception loss between broad-leaved deciduous and coniferous evergreen forests. The above results suggest that converting coniferous forests into broad-leaved forests can be used to increase water yield in these regions. [Copyright &y& Elsevier]

Summary: In Japan, forested areas are usually located upstream of urban and agricultural areas. Estimating annual water yield from such forested areas is therefore crucial for water resources management. For this purpose, estimating annual forest evapotranspiration is required. We developed an empirical model for estimating annual forest evapotranspiration E in Japan based on 43 catchment water balance datasets summarized from earlier publications. The model formulated E as E (mm)=31.4T (°C)+376, where T is mean annual air temperature. This model estimated E observed in forest catchments with an average 6% error relative to incident annual precipitation. This error was comparable to or smaller than the error included in precipitation data due to the spatial heterogeneity of precipitation. High-quality air temperature data are commonly available in Japan, thus this model is a practical tool for annual water yield estimates from forested areas and therefore water resources management. [Copyright &y& Elsevier]

• Evapotranspiration features differ in seasonal but are similar in annual scales. • Evapotranspiration can be fitted with single dominant factor in linear form. • Soil water is the main limitation of evapotranspiration in most cases in the region. • Improvement of soil water shifts dominant factors from soil water to energy. • The threshold of dominant factor shift can be determined by ROC curve. Evapotranspiration is an essential process of ecosystem water consumption and is controlled by meteorological factors and soil water conditions. In this study, evapotranspiration based on soil water budget was investigated with respect to major influencing factors during the growing seasons of 2012–2015 for two adjacent forest communities in the semiarid Loess Plateau region: a natural secondary forest dominated by oak (Quercus liaotungensis) and a plantation of exotic black locust (Robinia pseudoacacia). Based on the combination of precipitation, soil water storage, and evapotranspiration dynamics, four distinct periods were differentiated to explore the evapotranspiration response to the main meteorological factors. The correlation matrixes showed that, in most investigated days, evapotranspiration was limited by soil water storage, while an increase in soil water storage shifted dominance from water-related to energy-related factors. The stepwise regression of ≥5-day dry events in each period had a better fitness when paired with the relationship between the summations of evapotranspiration and dominant factors (R2 > 0.7, p < 0.01 for all) than the stepwise results for daily averages. A receiver operating characteristic (ROC) curve was applied to validate the division and determine thresholds. All divisions were thoroughly validated, and the soil water storage thresholds of the black locust (120.2 mm and 150.7 mm) were higher than those of the oak (105.8 mm and 137.9 mm). Our results suggest that the oak had an adaptive water consumption strategy, while the black locust had a higher sensitivity to soil water insufficiency. The method for determining the threshold of soil water storage to separate the dominant factors of evapotranspiration was validated. The approach may be applied to other semiarid forest communities with distinct evapotranspiration response patterns. [ABSTRACT FROM AUTHOR]

Summary: Annual forest evapotranspiration (ET) is highly variable among various sites. Zhang’s model () has been widely used for predicting the spatial variation in ET. The forest component of the model employs limiting theory and assumes constant annual potential evaporation (E 0 =1410mm) by regressing data recorded at 56 forest sites. However, most of the data used in determining E 0 were recorded for limited regions (Australia, African countries, and the United States). We summarized 829 forest ET data items obtained for sites around the world from earlier publications. Using the dataset, we showed that Zhang’s model overestimates forest ET in temperate and boreal regions with low annual mean temperature (T) owing to the E 0 value. We revised the E 0 term of Zhang’s model so as to consider the dependency of E 0 on T using the dataset. The revised model did not overestimate forest ET in temperate and boreal regions. Consequently, we recommend revising the E 0 term of Zhang’s model when predicting forest ET in these regions. [ABSTRACT FROM AUTHOR]