Search

In Japan, forests of Moso bamboo ( Phyllostachys pubescens, an exotic invasive giant bamboo) have naturalized and expanded rapidly, replacing surrounding broadleaved and coniferous forests. To evaluate impacts caused by these forest-type replacements on the hydrological cycle, soil-water content and its spatial variability in a Moso bamboo forest were compared with those in an adjacent evergreen broadleaved forest, in a case study of a stand in western Japan (northern Kyushu). The volumetric soil-water content averaged over depths between 0 and 60 cm was consistently higher in the bamboo stand than that in the broadleaved stand. These results contrast with previous studies comparing the soil-water content in Moso bamboo forests with that in other forest types. The sum of canopy transpiration and soil evaporation ( E) in the bamboo stand tended to be larger than that in the broadleaved stand. Small canopy interception loss was reported in the bamboo forest. Therefore, the large amount of E would counterbalance the small canopy interception loss in the bamboo forest. Differences in soil characteristics between the two stands may be the main factor causing differences in soil-water content. Spatial variation in soil-water content in the bamboo stand was larger than that in the broadleaved stand, confirming findings in a previous series of our study. This could happen because the well-developed root-system in the bamboo forest enhances preferential flow in the soil. To evaluate the effects of aggressive invasion of alien giant bamboo on the ecosystem functions, we recommend further studies measuring various hydrological components in various Moso bamboo forests. [ABSTRACT FROM AUTHOR]

• Two models to estimate the ratio of stemflow (SF) to gross rainfall (GR) in Japanese cedar and cypress plantations were developed using common forest inventory data. • Stand density (SD) exclusively determined the SF / GR. • A density-based SF / GR model with SD was developed for forest water management. • Stand-scale funneling ratio is related to mean diameter at breast height (D B H ¯). • A size-based SF/GR model with D B H ¯ and SD enables meticulous forest water management. Although stemflow (SF) had been regarded as a small portion of the gross rainfall (GR), recent studies have revealed that, depending on the forest stand structure, the SF/GR ratio should not be neglected. This study derived SF / GR estimation models using common forest inventory data. A set of SF/GR ratio and forest inventory data (stand density (SD), total basal area (BA), mean diameter at breast height (D B H ¯), mean tree height (H ¯), canopy cover (CC), and leaf area index (LAI)) was collected from previous studies of Japanese cedar and cypress plantations. To further investigate the relation between SF / GR ratio and forest stand structures, we examined additional stand-structure variables (mean basal area (B A ¯), mean stem surface area (S A ¯), and total stem surface area (SA)) derived from the inventory data, and the stand-scale funneling ratio (FR stand) evaluating the efficiency of funneling rainwater. Among all the stand-structure variables, SD exclusively determined the SF / GR ratio, providing the best-fitting positive single linear regression equation as a density-based SF / GR model with a root mean square error (RMSE) of 2.4%. Although this model is useful for practical forest water management because it requires only SD which is the most basic forest inventory data, it has a weak point in meticulous forest water management because it cannot reflect the effect of tree growth on SF / GR ratio. Thus, we developed a size-based SF / GR model (RMSE = 2.0%) based on the strong relationship between the FR stand and D B H ¯. This model is applicable to meticulous forest water management because it reflects the effects of not only SD but also tree growth by DBH on SF / GR ratio. These models derived from the common forest inventory data are potentially applicable to the evaluation and control of SF in forest water management. [ABSTRACT FROM AUTHOR]

Headwaters contribute a substantial part of the flow in river networks. However, spatial variations of streamflow generation processes in steep headwaters have not been well studied. In this study, we examined the spatio-temporal variation of streamflow generation processes in a steep 2.98-ha headwater catchment. The time when baseflow of the upstream section exceeded that downstream was coincident with the time when the riparian groundwater switched from downwelling to upwelling. This suggests that upwelling of the riparian groundwater increased considerably in the upstream section during the wet period, producing a shift in the relative size of baseflow between the upstream and downstream sections. The timing of fluctuations among hillslope soil moisture, hillslope groundwater and streamflow reveals that the hillslope contributed to storm flow, but this contribution was limited to the wet period. Overall, these results suggest that streamflow generation has strong spatial variations, even in small, steep headwater catchments. EDITOR A. Castellarin ASSOCIATE EDITOR X. Chen [ABSTRACT FROM AUTHOR]

Thinning results in more open-stand canopies and then immediately modifies the environmental factors that influence forest floor evaporation ( E f ). Thus, the changes in E f induced by thinning would play an important role in the forest water cycle, whereas few studies have reported this topic. This study analyzes the effect of strip thinning on E f , its spatial variation and identifies the factors influencing it in a Japanese cypress ( Chamaecyparis obtusa Endl.) plantation in Tochigi Prefecture, Japan. Strip thinning, which removed 50% of the stems, was conducted in a headwater basin during the period of October 11–November 5, 2011. The E f was monitored by weighing lysimeters before and after thinning. The daily E f was strongly correlated with the daily solar radiation ( R 2 = 0.62) followed by vapor pressure deficit ( R 2 = 0.41) below the canopy, whereas the soil water content had a poor effect on it in post-thinning. After thinning, the daily E f among the measuring points had no significant difference, indicating that the daily E f had a small spatial variation. This responded to the small spatial variability in the daily solar radiation under the canopy. Additionally, on an annual scale, thinning resulted in the daily mean E f increasing from 0.34 ± 0.23 to 0.68 ± 0.47 mm d −1 . The total E f increased by 97.6% from 124.0 to 245.0 mm. These findings indicate that E f composes a significant part of the forest water budget after thinning and emphasize the importance of E f measurements for management practices. This study also provides useful information for modeling the changes in hydrological processes at the forest floor and for evaluating the E f response to different management practices. [ABSTRACT FROM AUTHOR]

• Throughfall kinetic energy (TKE) can be affected by under-canopy dead branches. • The present unit TKE was much lower than that reported, with fewer/no dead branches. • Empirical unit TKE model only considering upper-canopy structures overestimates. • 6–15 sand-filled splash cups are appropriate for stand-scale TKE measurements. • Branch pruning may be unnecessary for soil erosion control. Among soil erosion processes, the initial stage of splash soil erosion caused by throughfall kinetic energy (TKE) plays a crucial role in soil conservation within forest ecosystems. Throughfall (TF) through the upper canopy structure considerably influences TKE in coniferous plantations. Recent studies have revealed that the under-canopy structure laden with dead branches in unmanaged coniferous plantations reduces the TF ; however, its specific impacts on TKE and appropriate sampling strategies remain unexplored. This study used 40 splash cups (4 for free kinetic energy and 36 for TKE) for one event (total: 600 splash cups for 15 events) in an unmanaged 36-year-old Japanese cypress plantation laden with dead branches. Additionally, unstratified and stratified Monte Carlo simulations were used to determine optimal sample sizes for stand-scale TKE estimation. Results demonstrated a strong correlation between TKE (J m−2) and TF (mm) (R 2 = 0.98) across all events. The stand-scale unit TKE of 12.5 J m−2 mm−1 was much lower than those in seven previous studies with fewer or no dead branches (range: 16.4 to 28.2, median: 18.8 J m−2 mm−1). The previously developed empirical stand-scale unit TKE model considering under-canopy structure solely exhibited a 1.7-fold overestimation. Among the stand structures, a positive relationship of TKE with the distance between a sampling point and its nearest trunk (D min) was observed, which was positively correlated with the lowest dead branch height. This indicated that under-canopy dead branches weakened the TKE , likely by reducing TF and raindrop fall velocity. Stratified Monte-Carlo simulation considering the D min related spatial patterns of TKE provided a more efficient approach for capturing variability. To achieve high precision with potential errors of ≤5–10 %, a total sample size of 6–15 was appropriate. Our findings implied that the presence of under-canopy dead branches mitigates the soil erosion risk in unmanaged Japanese cypress plantations. [ABSTRACT FROM AUTHOR]

Hydroxyl radical (HO ) photoformation rate ( R HO ) was determined in headwater stream samples from nitrogen (N)-saturated forests, (1) to quantify the sources of HO in headwater streams and (2) to evaluate the nitrate NO 3 - -induced enhancement of HO formation in stream water caused by N saturation in forested watersheds. Stream water fulvic acid extracted from the forested watersheds was used to quantify the contribution of dissolved organic matter (DOM) to R HO . The results showed that almost all (97%; 81–109%) R HO sources in our headwater stream samples were quantitatively elucidated; the photolysis of NO 3 - (55%; 34–75%), nitrite [N(III)] (2%; 0.5–5.2%), and DOM-derived HO formation, from which photo-Fenton reactions (18%; 12–26%) and the direct photolysis of fluorescent dissolved organic matter (FDOM) (22%; 10–40%), was successfully separated. FDOM, which accounted for 53% (24–96%) of DOM in total organic carbon bases, was responsible for HO formation in our headwater streams. High NO 3 - leaching caused by N saturation in forested watersheds increased R HO in the headwaters, indicating that N-saturated forest could significantly change photoinduced and biogeochemical processes via enhanced HO formation in downstream water. [ABSTRACT FROM AUTHOR]

Researchers and journalists in Japan recently proposed forest management as an alternative to dam reservoir development for water resource management. To examine the validity of the proposal, we compared the potential low-flow increase due to forest clearcutting with the increase due to dam reservoir development. Here, we focused on forest clearcutting as an end member among various types of forest management. We first analyzed runoff data for five catchments and found a positive correlation between annual precipitation and the low-flow increase due to deforestation. We then examined the increase in low-flow rates due to dam reservoir development (dQd ) using inflow and outflow data for 45 dam reservoirs across Japan. Using the relationship between annual precipitation and the low-flow increase due to deforestation, we estimated the potential increase in the low-flow rate for each dam reservoir watershed if forests in the watershed were clearcut (dQf ). Only 6 of the 45 samples satisfied dQf > dQd , indicating that the potential increase in the low-flow rate due to forest clearcutting was less than the increase due to dam reservoir development in most cases. Twenty-five of the 45 samples satisfied dQf <0.2 dQd , indicating the potential increase in the low-flow rate due to forest clearcutting was less than 20% of the increase due to dam reservoir development in more than half the cases. Therefore, forest management is far less effective for water resource management than dam reservoir development is in Japan. [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]

Lianas (woody climbers) have a greater amount of leaves relative to basal area or standing biomass than trees, and very wide vessels that permit efficient water transport. These features suggest that lianas possibly consume proportionally more water through transpiration than trees. Despite their potential importance, researchers have made only limited attempts to evaluate effects of lianas on forest water dynamics., We conducted sap flow measurements for 1 year using a thermal dissipation method for four species each of lianas and trees in a liana-rich, warm-temperate forest in Japan and estimated the contribution of lianas to stand canopy transpiration., Based on a calibration measuring water uptake rates from cut-stem ends, the actual sap flux ( Fd) in liana stems was several times greater than those estimated from the original calibration provided for the method. In the field, lianas showed an average of 2-4 times greater Fd than trees throughout the year. Except for this difference, diurnal and seasonal patterns of relative changes of Fd were similar in both groups. The whole-plant transpiration ( Qt) of sample plants was exponentially related to basal diameter for both lianas and trees; Qt of lianas increased more steeply with basal diameter than that of trees. By extrapolating the relationships between Qt and basal diameter to the inventory data of the study plot, we estimated that lianas contributed 12·8% to the annual stand canopy transpiration while comprising 2·3% of stand basal area, which probably reflected the top-heavy architecture of lianas., Our results indicate that the contribution of lianas to forest water dynamics may be several times greater than their contribution to forest basal area. This implies that a slight increase of liana abundance might have greater effects on water dynamics and, through competitions with trees for limited water, the carbon sequestration capacity of forests than expected from the increase in basal area. This study underlines the necessity of evaluating the relative importance of lianas to forest water dynamics in forests world-wide., A is available for this article. [ABSTRACT FROM AUTHOR]

In the large caldera of Mt. Aso, Japan, artificial grasslands were converted into forests of different species due to the decline of the livestock industry in this region. These changes in species composition are thought to have changed not only the transpiration rates ( E), but also the responses in E to variations in environmental conditions. For three introduced forest types, we monitored E using sap flux sensors and computed E with a multilayer model parameterized by independently obtained leaf-scale ecophysiological traits. Modeled E replicated the time series of measured E reasonably well, but did not reproduce a decrease in E lasting 20 days after a short rainless period in conifer plantation. Mean leaf-scale stomatal conductance of two deciduous broadleaved tree species was as low as that of trees under dry conditions in other studies, possibly an adaptation for the avoidance of excessive E during rainless periods. These results suggest that land use change influenced E and its response to the rainfall patterns of the region and that drought plays an important role in influencing species-specific E characteristics in this rainy region. The multilayer model in combination with sap flux measurements was found to be a useful tool not only for the extrapolation of E, but also for the detection of the unexpected events, as long as the measured parameter values capture the species-specific seasonality in leaf ecophysiological traits. [ABSTRACT FROM AUTHOR]

This study examined the effects of herbaceous plant roots on interrill erosion using two herbaceous species: clover (Trifolium repens) and oats (Avena sativa). We developed a simple rainfall simulator with relatively high normalized kinetic energy (KE; 23.2 J m−2 mm−1). Under simulated rainfall, we measured eroded soil for 42 boxes with various amounts of aboveground and belowground biomass. Aboveground vegetation had a significant effect on the soil erosion rate (SER). We found a clear negative relationship between the percent vegetation cover (c) and the SER. In contrast, plant roots showed no effects on the SER. The SER was not significantly different between the boxes with and without plant roots under similar c conditions. Thus, plant roots could have less of an effect on the SER under higher KE conditions. Editor M.C. Acreman Associate editor N. Verhoest [ABSTRACT FROM AUTHOR]

• 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]

Wood CO 2 efflux ( R wood ) is an important carbon cycling process in forest ecosystems and is less understood in Bornean tropical rainforests compared with that in Neotropics, which have differing biotic and abiotic characteristics. Bornean tropical rainforests have particularly higher aboveground biomass because of high stand densities of tall emergent trees, and no regular seasonal dry period. These properties may reflect specific R wood variation and higher annual R wood at the ecosystem scale (annual- R wood ) in Borneo. Hence, in this study, we investigated factors that affect inter-individual variation in chamber-based R wood on stem surfaces at breast height (chamber- R wood ) and estimated R wood at the ecosystem scale (ecosystem- R wood ) in a Bornean tropical rainforest. Subsequently, we examined temporal variation in ecosystem- R wood with environmental factors, estimated annual- R wood , and then evaluated the effects of large trees on ecosystem- R wood . Stem growth rates were the most significant predictor of inter-individual variation in chamber- R wood during all five measurement periods between 2012 and 2014. Accordingly, stem growth rates allowed accurate estimates of ecosystem- R wood , although chamber- R wood varied with diameter at breast height (DBH) and tree species in some measurement campaigns. Ecosystem- R wood decreased with soil moisture. Considering the inter-individual and temporal variation, annual- R wood was estimated at 7.06 ± 2.09 MgC ha −1 year −1 . This value was comparable to those determined in Neotropical forests, even though aboveground biomass in the present study site was approximately twice of those in Neotropical sites. Large trees with DBH >70 cm comprised 38% of aboveground biomass but accounted for only 23% of ecosystem- R wood because of the small portion of woody tissue surface area of the large trees. These data indicate that the stand density of large trees can considerably affect aboveground biomass but exert less influence on variation in ecosystem- R wood among various forests. [ABSTRACT FROM AUTHOR]

In the last several years, thinning has been conducted in coniferous plantations throughout Japan, mainly to secure water resources. Although canopy interception loss ( I c ) is a major component of evapotranspiration, this is among the first studies that have examined changes in I c while considering the effects of thinning in Japanese cedar ( Cryptomeria japonica ) forests, the most common type of plantation in Japan. We compared and contrasted three canopy interception models (Mulder, revised Gash, WiMo) before and after intensive thinning operations. The experimental Japanese cedar forest was intensively thinned with removal of 54% of all stems, reducing the basal area by 50% from 99.7 to 49.6 m 2 ha −1 . Prior to thinning, all three canopy interception models performed well with root mean square errors for the Mulder, revised Gash, and WiMo models of 2.96, 3.59, and 3.81 mm, respectively; while those after thinning were 1.32, 2.37, 2.38 mm, respectively. In addition, all three canopy interception models performed better than the mean before thinning as evaluated by the Nash–Sutcliffe model efficiency with values 0.51 (Mulder), 0.28 (revised Gash), and 0.19 (WiMo) but did not perform as well after heavy thinning. These results suggest that canopy interception models might not be applicable after intensive thinning of Japanese cedar forests. [ABSTRACT FROM AUTHOR]

Periodic droughts and extreme rainfall are predicted to become more common in the future; therefore, it is important to understand how soil N transformation processes driven by soil microbes respond to rainfall events. Differences in forest type, including those in the predominant mycorrhizal type, can have varying effects on soil N transformation. Therefore, we hypothesised that the response of the N transformation processes to rainfall events would differ between forest types, even those that are adjacently located. In this study, we generated a soil moisture gradient in adjacent dryland black locust (Robinia pseudoacacia , non-ectomycorrhizal [ECM]-type) and oak (Quercus liaotungensis , ECM-type) forests and measured the abundance and community composition of fungi and prokaryotes (including ammonia-oxidisers), extractable N content, and net N transformation rates in the soil. Increasing moisture was found to increase nitrate N content in the black locust forest but not in the oak forest. In the oak forest, the abundance of ECM fungi increased with increasing moisture, subsequently enhancing ECM fungal ammonium N uptake and limiting the N availability for ammonia oxidisers, which may reduce the nitrate N production by ammonia-oxidisers. Increased nitrate N uptake by ECM fungi may also result in low soil nitrate N content. The findings of this study indicate that the responses of the nitrate N dynamics to rainfall events can differ between adjacent forests and that this difference may be attributable to the presence of ECM fungi. Therefore, considering the forest mycorrhizal type is vital for predicating the response of forest N cycling under climate change. • A soil moisture variation was generated by an artificial rainfall experiment. • The response of nitrification to the moisture differed between two forest types. • Soil NO 3 − increased with increasing moisture in the black locust forest. • Soil NO 3 − content was always low in the oak (ectomycorrhizal-type) forest. • The increasing ECM fungi would reduce NO 3 − content in the oak forest. [ABSTRACT FROM AUTHOR]

Black locust (Robinia pseudoacacia) is widely planted throughout semiarid and subhumid regions of the Loess Plateau of China. Determining the changes in transpiration of this species in different climatic areas is important for revealing the acclimation mechanism of black locust and developing suitable forest management practices, particularly in the context of global climate change. Here, sap flow and canopy conductance of black locust plantation trees in semiarid (Yan'an) and subhumid (Yongshou) sites were quantified using Granier-type thermal dissipation probes and concurrent environmental observations from 2012 to 2017. Several physiological parameters were measured throughout the growing season. The results showed that sap flow was correlated with phenological factors across seasons within a year. However, interannual changes in sap flow were affected mainly by the reference evapotranspiration (ET 0) at the Yongshou site, and jointly by precipitation (P), soil water content, and P / ET 0 at the Yan'an site. Sap flow response to meteorological factors showed less discrepancy between pre- and post-rainfall periods at the Yan'an site. Moreover, canopy conductance fluctuated less with a wider range of vapor pressure deficit (VPD) and the slope of canopy resistance as a function of VPD was lower, indicating relatively lower sensitivity of stomatal conductance to environmental factors in Yan'an site. Physiological parameters, except for predawn leaf water potential, were significantly different between the two sites. The results suggested that black locust tended to reduce transpiration, modify leaf morphology, and improve water use efficiency to enhance its adaptability to the dryer site. The species changes stomatal regulation characteristics and general growth rate to acclimatize to distinct water habitats. • Sap flow characteristics of black locust differ between semiarid and subhumid sites. • Dominant environmental factors controlling transpiration varied with habitats. • Adaptability and responses to long-term and short-term drought are different. • Longterm soil water shortage weakened stomatal regulation and growth. • Future intensified drought potentially threatens the plantation stability. [ABSTRACT FROM AUTHOR]

Difficult access to 40-m-tall emergent trees in tropical rainforests has resulted in a lack of data related to vertical variations in wood CO2 efflux, even though significant variations in wood CO2 efflux are an important source of errors when estimating whole-tree total wood CO2 efflux. This study aimed to clarify vertical variations in wood CO2 efflux for emergent trees and to document the impact of the variations on the whole-tree estimates of stem and branch CO2 efflux. First, we measured wood CO2 efflux and factors related to tree morphology and environment for seven live emergent trees of two dipterocarp species at four to seven heights of up to ∼40 m for each tree using ladders and a crane. No systematic tendencies in vertical variations were observed for all the trees. Wood CO2 efflux was not affected by stem and air temperature, stem diameter, stem height or stem growth. The ratios of wood CO2 efflux at the treetop to that at breast height were larger in emergent trees with relatively smaller diameters at breast height. Second, we compared whole-tree stem CO2 efflux estimates using vertical measurements with those based on solely breast height measurements. We found similar whole-tree stem CO2 efflux estimates regardless of the patterns of vertical variations in CO2 efflux because the surface area in the canopy, where wood CO2 efflux often differed from that at breast height, was very small compared with that at low stem heights, resulting in little effect of the vertical variations on the estimate. Additionally, whole-tree branch CO2 efflux estimates using measured wood CO2 efflux in the canopy were considerably different from those measured using only breast height measurements. Uncertainties in wood CO2 efflux in the canopy did not cause any bias in stem CO2 efflux scaling, but affected branch CO2 efflux. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Physical process of canopy interception loss remains to be explained. [•] Rainfall partitioning to interception was similar between the stands. [•] The rate of interception increased with rainfall intensity. [•] Observed amount of interception was greater than estimated amount of evaporation. [•] We suggest that splash droplets transport by canopy ventilation is the primary process of interception loss. [ABSTRACT FROM AUTHOR]

To clarify characteristics of carbon (C) allocation in a Bornean tropical rainforest without dry seasons, gross primary production (GPP) and C allocation, i.e., above-ground net primary production (ANPP), aboveground plant respiration (APR), and total below-ground carbon flux (TBCF) for the forest were examined and compared with those from Amazonian tropical rainforests with dry seasons. GPP (30.61 MgC ha year, eddy covariance measurements; 34.40 MgC ha year, biometric measurements) was comparable to those for Amazonian rainforests. ANPP (6.76 MgC ha year) was comparable to, and APR (8.01 MgC ha year) was slightly lower than, their respective values for Amazonian rainforests, even though aboveground biomass was greater at our site. TBCF (19.63 MgC ha year) was higher than those for Amazonian forests. The comparable ANPP and higher TBCF were unexpected, since higher water availability would suggest less fine root competition for water, giving higher ANPP and lower TBCF to GPP. Low nutrient availability may explain the comparable ANPP and higher TBCF. These data show that there are variations in C allocation patterns among mature tropical rainforests, and the variations cannot be explained solely by differences in soil water availability. [ABSTRACT FROM AUTHOR]

Understanding radial and azimuthal variation, and tree-to-tree variation, in sap flux density (Fd) as sources of uncertainty is important for estimating transpiration using sap flow techniques. In a Japanese cedar (Cryptomeria japonica D. Don.) forest, Fd was measured at several depths and aspects for 18 trees, using heat dissipation (Granier-type) sensors. We observed considerable azimuthal variation in Fd. The coefficient of variation (CV) calculated from Fd at a depth of 0–20 mm (Fd1) and Fd at a depth of 20–40 mm (Fd2) ranged from 6.7 to 37.6% (mean = 28.3%) and from 19.6 to 62.5% (mean = 34.6%) for the ­azimuthal directions. Fd at the north aspect averaged for nine trees, for which azimuthal measurements were made, was ­obviously smaller than Fd at the other three aspects (i.e., west, south and east) averaged for the nine trees. Fd1 averaged for the nine trees was significantly larger than Fd2 averaged for the nine trees. The error for stand-scale transpiration (E) estimates caused by ignoring the azimuthal variation was larger than that caused by ignoring the radial variation. The error caused by ignoring tree-to-tree variation was larger than that caused by ignoring both radial and azimuthal variations. Thus, tree-to-tree variation in Fd would be more important than both radial and azimuthal variations in Fd for E estimation. However, Fd for each tree should not be measured at a consistent aspect but should be measured at various aspects to make accurate E estimates and to avoid a risk of error caused by the relationship of Fd to aspect. [ABSTRACT FROM PUBLISHER]

Abstract: In western Japan, Moso bamboo (Phyllostachys pubescens) forests have been expanding by replacing surrounding forests (e.g., coniferous plantation forests), which raises concerns about possible changes in terrestrial water and carbon cycles. Canopy conductance (G c ) is a critical parameter for determining canopy transpiration and photosynthesis. To clarify the characteristics of G c for Moso bamboo forests, we calculated G c during a growing season for a Moso bamboo forest on the basis of canopy transpiration measurements made using the sap-flux method, and then compared the G c value with values for coniferous plantation forests in western Japan. G c was primarily related to the vapor pressure deficit and secondarily to solar radiation, similar to the results obtained for other temperate forests. Under light-saturated conditions, G c for the bamboo forest was approximately twice that for the coniferous plantation forests despite the lower leaf area index for the bamboo forest. This implies higher canopy transpiration and photosynthesis for the bamboo forest, and therefore possible changes in terrestrial water and carbon cycles due to the replacement of coniferous plantation forests by bamboo forests. [Copyright &y& Elsevier]

The sensitivity of land surface energy partitioning to near-surface air temperature ( T) is a critical issue to understand the interaction between land surface and climatic system. Thus, studies with in situ observed data compiled from various climates and ecosystems are required. The relations derived from such empirical analyses are useful for developing accurate estimation methods of energy partitioning. In this study, the effect of T on land surface energy partitioning is evaluated by using flux measurement data compiled from a global network of eddy covariance tower sites (FLUXNET). According to the analysis of 25 FLUXNET sites (60 site-years) data, the Bowen ratio is found to have a linear relation with the bulk surface resistance normalized by aerodynamic and climatological resistance parameters in general, of which the slope and intercept are dependent on T. Energy partitioning in warmer atmosphere is less sensitive to changes in land surface conditions. In addition, a negative relation is found between Bowen ratio and T, and this relation is stronger above less vegetated surface and under low vapor pressure deficit and low received radiative energy condition. The empirical results obtained in this study are expected to be useful in gaining better understanding of alternating surface energy partitioning under increasing T. [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]

The prevalence of forestry practices such as thinning and pruning have gradually decreased since the 1980s. Researchers have noted an increased flood risk with decreased forestry practices for coniferous plantations in Japan on the basis of infiltration and overland flow measurements at a plot scale (typically several square meters). However, no studies have examined changes in peak flow with decreased forestry practices at a watershed scale (typically several tens or hundreds of square kilometers) even though flood disasters generally occur at this scale in Japan. We examined changes in frequency distributions of daily precipitation (P) and runoff (Q) during the period 1979–2007 at the Terauchi watershed, where forestry practices are known to have decreased. For this purpose, we divided P and Q data into 14 and 15 classes according to the magnitude, respectively, and examined changes in the frequency for each class during the period. We observed no significant increasing trend for any P or Q class. Even when taking into account the effect of interannual variations in precipitation on the frequency for each Q class, there was no significant increasing trend in the frequencies except for two Q classes with moderate Q values. These results suggest that the increase in flood risk due to decreased forestry practices might be less than expected. [Copyright &y& Elsevier]

In pine wilt disease (PWD), embolized tracheids arise after virulent pine wood nematodes (PWN), Bursaphelenchus xylophilus, invade the resin canal of pine tree; infected pine trees finally die from significant loss of xylem water conduction. We used a compact magnetic resonance imaging system with a U-shaped radio frequency (rf) probe coil to reveal the developmental process of the xylem dysfunction in PWD. Multiple cross-sectional slices along the stem axis were acquired to periodically monitor the total water distribution in each 1-year-old main stem of two 3-year-old Japanese black pines (Pinus thunbergii) after inoculation of PWN. During the development of PWD, a mass of embolized tracheids around the inoculation site rapidly enlarged in all directions. This phenomenon occurred before the significant decrease of water potential. Some patch-like embolisms were observed at all monitoring positions during the experimental period. Patchy embolisms in a cross-section did not expand, but the number of patches increased as time passed. When the significant decrease of water potential occurred, the xylem dysfunctional rate near the inoculation point exceeded 70%. Finally, almost the whole area of xylem was abruptly embolized in all cross-sections along the stem. This phenomenon occurred just after water conduction was mostly blocked in one of the cross-sections. Thus, it appears that the simultaneous expansion of embolized conduit clusters may be required to induce a large-scale embolism across the functional xylem. Consequently, xylem dysfunction in infected trees may be closely related to both the distribution and the number of PWN in the pine stem. [ABSTRACT FROM AUTHOR]

Boreal forests play an important role in the global balance of energy and CO2. Our previous study of elaborate eddy covariance observations in a Siberian boreal larch forest, conducted both above the forest canopy and at the forest floor, revealed a significant contribution of latent heat flux (LE) from the cowberry understory to the whole ecosystem LE. Thus, in the present study, we examined what factors control the partitioning of whole ecosystem LE and CO2 flux into the understory and overstory vegetation, using detailed leaf-level physiology (for both understory and overstory vegetation) and soil respiration property measurements as well as a multilayer soil-vegetation-atmosphere transfer (SVAT) model. The modeling results showed that the larch overstory's leaf area index (LAI) and vertical profile of leaf photosynthetic capacity were major factors determining the flux partitioning in this boreal forest ecosystem. This is unlike other forest ecosystems that tend to have dense LAI. We concluded that control of the larch overstory's LAI had a relationship with both the coexistence of the larch with the cowberry understory and with the water resources available to the total forest ecosystem. [Copyright &y& Elsevier]

Abstract: In the semiarid Loess Plateau region of China, ecosystems are frequently affected by water shortages. Late spring and early summer are periods when forest communities tend to suffer from soil drought. To clarify the water-use strategies of the main species in this area, the xylem sap flow of trees from three species in the field was monitored for three successive periods in summer using Granier-type thermal dissipation probes. Vapor pressure deficit (VPD), solar radiation (R s) and soil moisture had varying influences on sap flux density (F d) in the species. Normalized F d values could be fitted to VPD using an exponential saturation function, but the fit was better with a derived variable of transpiration (VT), an integrated index calculated from VPD and R s. From differences in model coefficients, the species were roughly divided into two types with contrasting drought sensitivity. The exotic Robinia pseudoacacia was defined as drought-sensitive type. It showed higher sapflow increases in response to rainfall, suggesting a high water demand and high influence of soil water conditions on transpiration. This species showed relatively late stomatal response to increasing VPD. The wide-peak pattern of diurnal sapflow course also suggests relatively low stomatal regulation in this species. The drought-insensitive type consisted of the naturally dominant Quercus liaotungensis and an indigenous concomitant species, Armeniaca sibirica, in the forest. The sap flow of these species was not very sensitive to changes in soil water conditions. The results suggest that typical indigenous species can manage the water consumption conservatively under both drought and wet conditions. Variations in water use strategies within indigenous species are also detected. [ABSTRACT FROM AUTHOR]

Temperature data in the mountain forest regions are often extrapolated from temperature data recorded at base stations at lower elevation. Such extrapolation is often based on elevation differences between target regions and base stations at low elevation assuming a constant temperature lapse rate throughout the year. However, this assumption might be problematic where slope circulation is active and decoupled from the regional circulation. To model the seasonal change in the lapse rate, the authors compared daily maximum ( Tmax) and minimum temperatures ( Tmin) observed at a mountain forest site (Kog–Ma; 1300-m altitude) with those observed at the bottom of the basin (Chiang–Mai; 314-m altitude) in northern Thailand, where slope circulation is active and decoupled from the regional circulation. The difference in Tmax between Kog–Ma and Chiang–Mai (Δ Tmax; Kog–Ma minus Chiang–Mai) was relatively unchanged throughout the year. However, the difference in Tmin between Kog–Ma and Chiang–Mai (Δ Tmin) changed seasonally. Thus, assuming a constant lapse rate throughout the year could cause large errors in extrapolating Tmin data in mountainous areas in northern Thailand. The difference Δ Tmin was related to nighttime net radiation (Rn), suggesting that nocturnal drainage flow affects the determination of Δ Tmin. This relationship would be useful in formulating seasonal changes in the lapse rate for Tmin. As Rn data are generally unavailable for meteorological stations, an index that relates to the lapse rate for Tmin and is calculated from Tmax and Tmin data is proposed. This index might be useful for accurately estimating Tmin values in mountainous regions in northern Thailand. [ABSTRACT FROM AUTHOR]

In this study, we aimed to assess how sample sizes affect confidence of stand-scale transpiration (E) estimates calculated from sap flux (Fd) and sapwood area (AS_tree) measurements of individual trees. In a Japanese cypress plantation, we measured Fd and AS_tree in all trees (n = 58) within a 20 x 20 m study plot, which was divided into four 10 x 10 subplots. We calculated E from stand AS_tree (AS_stand) and mean stand Fd (JS) values. Using Monte Carlo analyses, we examined the potential errors associated with sample sizes in E, AS_stand and JS using the original AS_tree and Fd data sets. Consequently, we defined the optimal sample sizes of 10 and 15 for AS_stand and JS estimates, respectively, in the 20 x 20 m plot. Sample sizes larger than the optimal sample sizes did not decrease potential errors. The optimal sample sizes for JS changed according to plot size (e.g., 10 x 10 and 10 x 20 m), whereas the optimal sample sizes for AS_stand did not. As well, the optimal sample sizes for JS did not change in different vapor pressure deficit conditions. In terms of E estimates, these results suggest that the tree-to-tree variations in Fd vary among different plots, and that plot size to capture tree-to-tree variations in Fd is an important factor. The sample sizes determined in this study will be helpful for planning the balanced sampling designs to extrapolate stand-scale estimates to catchment-scale estimates. [ABSTRACT FROM AUTHOR]

Abstract: This study was undertaken to identify critical and practical factors explaining spatial variations in soil respiration and to estimate stand-scale soil respiration in an aseasonal tropical rainforest on Borneo Island. To this aim, we conducted soil respiration measurements at 25 points in a 40m×40m subplot of a 4ha study plot between 2002 and 2006, and examined the spatial variation in soil respiration averaged over the 4 years in relation to soil, root, and forest structural factors. In addition, we examined the spatial representativeness of soil respiration measured in the subplot using a specific scaling procedure. Consequently, we found significant positive correlation between the soil respiration and forest structural parameters such as the mean diameter at breast height (DBH), total basal area, and maximum DBH within 6m of the measurement points. The most important factor was the mean DBH within 6m of the measurement points, which had a significant linear relationship with soil respiration. Using the derived linear regression and an inventory dataset, we estimated the 4ha plot-scale soil respiration. The 4ha plot-scale estimation (6.0μmolm−2 s−1) was nearly identical to the subplot-scale measurements (5.7μmolm−2 s−1), which were roughly comparable to the nocturnal CO2 fluxes calculated using the eddy covariance technique. In addition, we discuss characteristics of the stand-scale soil respiration at this site by comparing with those of other forests reported in previous literature in terms of the soil C balance. Soil respiration at our site was noticeably greater, relative to the incident litterfall amount, than soil respiration in other tropical and temperate forests probably owing to the larger total belowground C allocation by emergent trees. Overall, this study suggests the arrangement of emergent trees with larger DBH and their belowground C allocation could be primary factors controlling spatial variations in soil respiration in the tropical rainforest. [Copyright &y& Elsevier]

Abstract: Plant–soil system patterns and processes along a slope are among the greatest causes of uncertainty in estimating watershed-scale transpiration (E). Tree-to-tree and radial variations in xylem sap flux density (F d), in addition to tree biometrics, were measured over a 2-year period (2005–2006) in two slope stand positions. The areas of interest consisted of an upper slope plot (UP) and a lower slope plot (LP) in a Japanese cedar (Cryptomeria japonica D. Don) forest watershed and the environmental controls of stand E for each plot were compared. Canopy stand E (E C) and canopy stomatal conductance (G C) in the UP were less than those in the LP during the growing season, while those in the UP were greater than those in the LP over winter. In addition, mean stand F d (J S) in the UP was greater than that in the LP over winter, but J S values were similar in the UP and LP except in the winter, which allows us to extrapolate watershed-scale E based on J S estimated from F d measurements of a partial stand in the watershed. However, this relationship contains a bias and differed between 2005 and 2006. Although there were significant differences in soil moisture conditions between the UP and LP in both years, a systematic relationship between the similarity in J S and soil moisture conditions was not found. The bias was due to a tendency for J S in the LP to be greater than that in the UP in 2006. This tendency was amplified because J S in the LP was greater than that in the UP around an atmospheric humidity deficit (D) of 1–1.5kPa and frequencies of this D range were higher in 2006 than in 2005. The greater J S in the LP at D ∼1–1.5kPa could be explained by the difference in the response of G C to D between the UP and LP. Our results suggest this to be the cause of the similarity in J S values for the UP and LP and for the occasional abortion of its similarity. However, even when the bias or the occasional deviation is disregarded, the error in estimating stand E from a partial stand is so small that it is comparable to an F d measurement error. For example, the error when using only the LP was 6.6% for stand E. [Copyright &y& Elsevier]

Summary: This study aimed to clarify the effects of antecedent rain history on particulate phosphorus (PP) loss in a small mountainous watershed covered primarily with a plantation forest of Japanese cypress (Chamaecyparis obtusa). We analyzed stream discharge and PP concentration at 15–60min intervals during 24h in eight rain events with different discharge levels. The PP concentration versus stream discharge (PPC–Q) relationships exhibited clockwise hysteresis loops for each of the eight events monitored. Discharge could explain changes in PP concentration on the falling but not rising limb of the hydrograph. On the rising limb, a positive relationship between the rate of changes in discharge (dQ/dt) and the PP load (dL/dt) was found for each event. This indicates that a large amount of PP is strongly pulsed at times of rapidly increased discharge. These results suggest that dQ/dt is the driving force behind PP supply and the primary control on the clockwise hysteresis loop of PPC–Q relationship. There was a strong negative correlation between the antecedent precipitation index and the slope of the dL/dt versus dQ/dt relationship. This shows that a rapid increase in PP load occurs even with slight increases in discharge as antecedent moisture conditions become drier. The soil water repellency and rapid runoff response following dry conditions support that soil desiccation increases the PP supply associated with soil erosion via overland flow. Therefore, we concluded that the antecedent rain history affects the mobility of PP via soil desiccation. The findings of this study will fill gaps in our understanding of temporal variations in released fine sediment and associated PP as reported in previous studies. [Copyright &y& Elsevier]

Abstract: Many studies have reported tree growth reduction in forests with pedestrian trampling, implying a reduction of tree transpiration in such forests. We undertook observations of tree transpiration based on the heat-pulse method in a forest (Lithocarpus edulis) with pedestrian trampling. We prepared trampled and control plots in the forest. Tree transpiration in the trampled plot was reduced compared to that in the control plot after precipitation with a small-precipitation period preceding this. No difference was observed between plots in the small-precipitation period itself; during which tree transpiration was limited in both plots. After the period, tree transpiration recovery was not as complete in the trampled plot as in the control plot. This was caused by incomplete soil matric potential recovery at 20 cm and deeper in the trampled plot due to a lower infiltration rate. We believe this study is the first to report reduction of tree transpiration in a forest with pedestrian trampling. [Copyright &y& Elsevier]

We determined the amount of information needed to estimate watershed-scale transpiration in a Japanese cedar (Cryptomeria japonica D. Don) forest from sap flow measurements of individual trees. Measurements of tree biometrics (diameter at breast height (DBH) and tree sapwood area (AS_tree)), and tree-to-tree and radial variations in xylem sap flux density (Fd) were made in two stand plots, an upper slope plot (UP) and a lower slope plot (LP), during a growing season characterized by significant variations in environmental factors. We then investigated how mean stand sap flux density (JS) and a tree stem allometric relationship (DBH--AS_tree) varied between the stands. Appropriate sample sizes for estimating representative JS values were determined. Both a unique and a general function allowed description of the allometric relationship along the slope, but the data for its formulation was required for both the UP and LP. Values of JS in the UP and LP were similar during the study period despite differences in tree density and size between the plots, implying that JS measured in a partial stand in a watershed is a reasonable estimate of JS in other stands in the watershed, and that stand sapwood area calculated from AS_tree is a strong determinant of water use in a forest watershed. To estimate JS in both the UP and LP, it was necessary to sample at least 10 trees in each plot. [ABSTRACT FROM AUTHOR]

Abstract: To scale sap flux density (F d) measurements of individual trees to stand level transpiration (E), the mean stand F d (J S) is among the most important factors, because E is frequently estimated as a product of J S and stand sapwood area. Major uncertainties in J S estimations are caused by tree-to-tree and radial variations in F d. Thus, by using the Monte Carlo sampling technique with original tree-to-tree F d data measured at several depths, we examined how many trees and radial depths need to be sampled for calculation of appropriate J S. In this study, F d was measured in 14 mature Japanese cedar (Cryptomeria japonica) trees at several radial depths, 0–2, 2–4 and 4–6cm, using Granier-type sensors. The results revealed that the potential error in J S with the largest available sample size was not stable even though radial profiles in F d for all sample trees were measured. They also showed that to consider radial variation in F d it might be necessary to sample at least six trees, but not necessarily more than this. The results imply that, for E estimations, there is more tree-to-tree variation in F d than in radial variation in F d. [Copyright &y& Elsevier]