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A larch forest in eastern Siberia was characterized by the presence of two distinct storeys, the overstorey with a small leaf area index (LAI) and a dense understorey with a relatively large LAI. To understand the roles of the overstorey and understorey in forest-atmosphere water exchange, canopy conductance ( Gc), a critical parameter used in determining the energy and mass exchange, was calculated on the basis of latent heat flux above the overstorey and understorey, measured separately. Results showed that Gc for the overstorey ( Gco) and understorey ( Gcu) experienced different seasonal fluctuations. Gco was smaller than Gcu during periods of leaf expansion and leaf fall and showed an increasing trend until 1 month after the onset of leaf expansion. In contrast, a sharp decrease in Gco was observed immediately before onset of leaf fall. Furthermore, Gco was slightly larger than Gcu during the fully foliated period. A simple model using solar radiation and vapour pressure deficit ( D) as inputs successfully reproduced the Gc in fully foliated periods with acceptable accuracy. Furthermore, both the understorey and overstorey in this study have a large reference Gc ( Gc at D = 1 KPa) than their counterparts of other boreal forests and would not be able to sustain a constant leaf-soil water potential difference as D increases. We speculated that this confers the forest with an advantage allowing it to be able to sustain carbon assimilation during large D days and thus provides for the survival of the ecosystem during the short growing season at this site. Copyright © 2014 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]

Nitrogenous air pollutants including nitrogen dioxide (NO), nitric acid (HNO), nitrate (NO), ammonia (NH), ammonium (NH), and nitrous acid (HONO) were characterized at an urban forested (UF) site in Hiroshima and at a suburban forested (SF) site in Fukuoka, western Japan, using an annular denuder system for 1 year from May 2006 to May 2007 to compare the concentrations and chemical species of atmospheric nitrogenous pollutants between UF and SF sites. The proximity of the urban area was reflected in higher NO concentrations at the UF site than at the SF site. NO was more oxidized at the SF site because it is farther from an urban area than the UF site, which was reflected in higher concentrations of HNO at the SF site than the UF site. HNO and acidic sulfate is neutralized by NH, existing as ammonium nitrate (NHNO) and ammonium sulfate [(NH)SO] at the UF site. At the SF site, acidic sulfate is neutralized by NH, existing as (NH)SO, but NHNO, had scarcely formed at the SF site. A much higher HONO concentration was observed at the UF site than at the SF site, especially in winter and spring at night, which could be explained by higher NO concentrations at the UF site because of its proximity to an urban area and stagnant meteorological conditions. Atmospheric HONO determination was critical in evaluating the possibility of damage to trees in UF areas. [ABSTRACT FROM AUTHOR]

Sap flow techniques are practical tools for estimating tree transpiration. Though many previous studies using sap flow techniques did not consider azimuthal variations of sap flux density ( F) on xylem trunk to estimate tree transpiration, a few studies reported that ignoring the azimuthal variations in F could cause large errors in tree transpiration estimates for some tree species. Therefore, examining azimuthal variations in F for major plantation tree species is critical for estimating tree transpiration. Using the thermal dissipation method, we examined azimuthal variations in F in six trees of Japanese cypress Chamaecyparis obtusa (Sieb. et Zucc.) Endl., which is one of the most common plantation tree species in Japan. We recorded considerable variations among F at four different azimuthal directions. The F value for one aspect was more than 100% larger than those for the other aspects. We calculated differences between tree transpiration estimates based on F for one to three azimuthal directions and those based on F for four aspects. The differences relative to tree transpiration estimates based on F for four aspects were typically 30, 20, and 10% in accordance with the F for one, two, and three measurement aspects, respectively. This finding indicates that ignoring azimuthal variations could cause large errors in tree transpiration estimates for Japanese cypress. [ABSTRACT FROM AUTHOR]

Abstract: In western Japan, Moso bamboo (Phyllostachys pubescens) forests have been expanding by replacing surrounding vegetation such as coniferous plantation forests and natural broadleaved forests. It has been speculated that the replacement of surrounding vegetation by bamboo forests could alter the vegetation water cycle and available water resources. We quantified stand-scale transpiration (E) in a bamboo forest on the basis of sap-flux measurements and compared the E value with values for coniferous forests. The annual E was estimated to be 567mm. Seasonal trends in E primarily corresponded to seasonal trends in the vapor pressure deficit. Annual E for the bamboo forest was higher than that for the coniferous forests by 12% of annual precipitation (P). This difference in annual E is comparable with the difference in annual interception evaporation (I) relative to P between bamboo and coniferous forests; previous studies reported lower I for bamboo forests by ∼10% of P. Thus, the sum of E and I was comparable for bamboo and coniferous forests. As this study is the first measuring E of bamboo forests, further studies are required to examine the generality of our results. [Copyright &y& Elsevier]

Abstract: The applicability of sap flux (F d ) measurements to bamboo forests has not been studied. This study was undertaken to establish an optimal and effective design for stand-scale transpiration (E) estimates in a Moso bamboo forest. To this aim, we validated F d measurements in Moso bamboos in a cut bamboo experiment. In addition, we analyzed how sample sizes affect the reliability of E estimates calculated from F d and conducting culm area (A S_b ). In the cut bamboo experiments, we found that F d measurement using a 10mm probe was a valid means of determining the water-use behavior of a Moso bamboo, although a specific correction was needed. Furthermore, we calculated E from stand A S_b (A S_stand) and mean stand F d (J S ). Employing Monte Carlo analysis, we examined potential errors associated with sample size in E, A S_stand, and J S using an original dataset with A S_b and F d measured for 40 and 16 individuals, respectively. Consequently, we determined the optimal sample size for both A S_stand and J S estimates as 11. The optimal sample sizes for J S were almost the same under different vapor pressure deficit and soil moisture conditions. The optimal sample size for J S at the study site was less than that of a coniferous plantation in the same region probably owing to small individual-to-individual variations in sap flux in the Moso bamboo forest. Our study concludes that sap flux measurements are an applicable technique for assessing water use in Moso bamboo forests. [ABSTRACT FROM AUTHOR]

In recent years, moso bamboo ( Phyllostachys pubescens) forest areas in Japan have rapidly expanded, and bamboo is now invading nearby natural or plantation forests. To date, only one study has examined the rainfall interception of a moso bamboo forest. In that study, it was reported that the interception ratio (interception/rainfall) of the bamboo forest did not exceed the interception ratios of other natural and plantation forests ( n = 4) in Japan. To expand the current state of knowledge about rainfall interception of bamboo forests, we measured throughfall and stemflow at another bamboo forest site. Annual rainfall ( Rf), throughfall ( Tf), and stemflow ( Sf) during the measurement period were 2,105, 1,556, and 322 mm, respectively. Annual rainfall interception at the plot ( I) was 228 mm. Tf/Rf, Sf/Rf, and I/Rf were 73.9, 15.3, 10.8%, respectively. I/Rf was less than 20% throughout the year except in October, the month with lowest rainfall. We also summarized rainfall interception data from 19 other natural and plantation forests. The I/Rf value of our site did not exceed the I/Rf values of these natural and plantation forests ( n = 19). Our data will be useful for assessing changes in water resources that result from replacement of natural or plantation forests by bamboo forests. [ABSTRACT FROM AUTHOR]

Abstract: Several previous studies in Japan have examined differences in rainfall interception amounts induced by differences in forest properties by comparing the annual rainfall interception ratios (annual rainfall interception divided by annual rainfall) from various sites without considering variations in meteorological conditions between sites. Rainfall interception actually depends on meteorological conditions as well as forest properties. This study examined variations in the annual interception ratio relating to the variation in annual rainfall, which would be the primary factor relating to the interception ratio, across Japan with the use of a rainfall interception model assuming the same forest properties (i.e., the canopy storage capacity, canopy closure, leaf area index (LAI), and the bulk coefficient for sensible heat transfer). The ratio ranged between 0.12 and 0.24 across Japan and was highly correlated to annual rainfall. This indicates that considering the variation in annual rainfall is critical for assessing the difference in rainfall interception amounts induced by forest properties. We reconsidered the results of previous studies in Japan that compared annual interception ratios between sites with different forest properties: (i) there is no clear difference in interception amounts between broadleaf and coniferous forests and (ii) there is a positive correlation in stem density and interception amounts for coniferous forests. These results still held when considering differences in annual rainfall between sites. [Copyright &y& Elsevier]

Abstract: Annual ring growth of Quercus liaotungensis trees in natural forests bounded by desertified region in the Loess Plateau of China was investigated for the evidence of climatic influence. Increment cores were sampled and cross-dated for 120 trees from six stands 0.5–2.5km apart. Site tree-ring chronologies were created using general dendrochronological techniques. The results of correlation analyses between tree-ring indices and monthly climatic variables indicated that radial growth was positively correlated with precipitation in September of the previous year and that from April to June of the current year. Ring widths were negatively affected by temperature during spring and summer. In contrast, mild temperature in the previous October showed a positive influence. The results suggest that precipitation is important in the early growing season when soil and air are dry, and that high temperatures tend to reduce radial growth in this region. September rainfalls and a warm October may provide conditions that facilitate carbon storage, favor soil microbial activity, and promote root growth and shoot maturation against detrimental effects of stresses in the following seasons. There were also some differences among plots in the effects of both climatic variables probably as a result of different structures and geographical conditions that modified microenvironments. The results may contribute to the reforestation management of the area. It is expected that Q. liaotungensis forests should be ecologically established in this region on shady and half-shady slopes where air and soil drought stresses are not serious. [Copyright &y& Elsevier]

Abstract: Estimations of stand sapwood area (A S_stand) are among the most critical factors for determining stand transpiration (E) using sap flux measurements. A S_stand is generally estimated using stem diameter (DBH) data measured for all trees in a stand and an allometric equation that describes the relationship between DBH and sapwood area (A S_tree) based on available allometric data. To examine the errors in E that are generated when using the allometric equation with a small sample size, the Monte Carlo sampling technique was used with an original allometric data set. In this study, all trees (921 Cryptomeria japonica and 1226 Chamaecyparis obtusa) in the studied stands provided the original allometric data (DBH and A S_tree). Monte Carlo simulations allow the number of sample trees required for an appropriate E estimate to be derived. The results revealed that potential errors in the E estimate were almost stable with a sample size of over 20 for both Cr. japonica and Ch. obtusa. This implies that at least, but not more than, 20 trees are necessary for the allometric equation when estimating E for both species. [Copyright &y& Elsevier]

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]

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]

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]

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]