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In this paper, we present an investigation of interspecies differences in transpiration of the 2 most common plantation forest tree species in Japan, both in the family Cupressaceae with different northern limits of native distribution, Japanese cypress (Hinoki; Chamaecyparis obtusa Sieb. et Zucc.) and Japanese cedar (Sugi; Cryptomeria japonica D. Don). The stem sap flow rate was measured in 2 nearby stands of similar leaf area index in a 42-year-old plantation. Single-tree and stand-scale transpiration rates ( Etre and Esta, respectively) were observed during an ideal autumn environment. At the stand scale, mean sap flux density of Hinoki was greater than that of Sugi, whereas total sapwood area per ground area was smaller in Hinoki than Sugi. Because the 2 variables had counterbalancing effects on transpiration, Esta of Hinoki was similar to (94% of) that of Sugi. This offset was also found between the mean Etre of the 2 species. Esta was similar between the stands from May to October, whereas Esta of Sugi was notably greater than that of Hinoki from February to April. During these 3 months, the difference in cumulative Esta was 21.7 mm, which accounted for 79% of the difference in annual Esta between Hinoki and Sugi (192 and 219 mm/year, respectively). We found that canopy conductance ( Gc) and its sensitivity to the mean vapour pressure deficit during daylight hours in Sugi were particularly high in early spring, whereas those in Hinoki shifted gradually throughout the growing season. This difference was related to the optimal temperature of Gc in Sugi, which was approximately 10 °C lower than that in Hinoki. Our results suggest that plantations of water-conserving species such as Hinoki produce timber slowly but yield water resources generously. Moreover, for plantations of trees sensitive to high temperature, such as Sugi, managers should be concerned about possible future decline caused by anticipated global warming. [ABSTRACT FROM AUTHOR]

Stand transpiration ( E) estimated using the sap flux methods is affected by the azimuthal, radial, and tree-to-tree variations of sap flux. Although several studies have examined the relative importance of the three variations in estimating E, the seasonality of the three variations remains unknown. In the current study, we attempted to clarify whether the relative importance of these three variations could show seasonal changes. Using sap flux data measured in a subtropical cloud forest from August 2010 to July 2011, we calculated the differences resulting from omitting the three variations in estimating E. The effects of the three variations in estimating E showed seasonality. The azimuthal and tree-to-tree variations were more pronounced during winter, whereas the radial variation was more pronounced during summer. However, the effect of tree-to-tree variation was consistently much larger than the other two variations throughout the study period. The tree-to-tree variation is more important in estimating E monthly, seasonally and annually than both the azimuthal and radial variations, although all three variations have shown seasonality. In addition, the sensor allocation for summer would be acceptable for the practical estimation of E if aiming at the long time scale. [ABSTRACT FROM AUTHOR]

This study offers an unprecedented opportunity to estimate total sapwood area over an entire catchment (Ascat/Ag) using small-footprint light detection and ranging technology with a minimal amount of labour in field. Forty-two-year-old plantations of Japanese cypress (Hinoki; Chamaecyparis obtusa Sieb. et Zucc.) and Japanese cedar (Sugi; Cryptomeria japonica D. Don) vegetated the 2.98 ha experimental catchment. Field observations identified diameter at breast height (DBH) of all trees and produced the relationship between DBH and tree sapwood area (Astre). The sum of Astre generated actual values of Ascat/Ag. For light detection and ranging data analyses, local maximum filtering revealed height of tree apices (H) and tree number (N) with 9% omission errors. A novel process was developed to identify tree species by their apices based on height of the apices and canopy roughness. Four methods were tested. In Methods A-C, H was converted to Astre directly or via DBH, then, the sum of Astre created Ascat/Ag. H-Astre or H-DBH relationships were varied irrespective of labour-intensive measurements, and Ascat/Ag was underestimated up to 85% of actual value because of the smaller N. On the other hand, in Method D, ready-made stand density management diagrams (SDMDs) overestimated mean DBH. However, a product of overestimated mean Astre and the underestimated N was almost identical to the actual Ascat/Ag. The estimates were 84% and 95% of the true Ascat/Ag in Hinoki and Sugi, respectively, and the former will be more precise if the SDMD is suitable for the site as indicated through sensitivity analysis. [ABSTRACT FROM AUTHOR]

Previous studies have revealed that changes in forest structure due to management (e.g., thinning, aging, and clearcutting) could affect the forest water balance. However, there are unexplained variability in changes in the annual water balance with changing structure among different sites. This is the case even when analyzing data for specific species/regions. For a more advanced and process-based understanding of changes in the water balance with changing forest structure, we examined transpiration ( E ) observed using the sap-flux method for 14 Japanese cedar and cypress plantations with various structure (e.g., stem density and diameter) in Japan and surrounding areas and developed a model relating E with structural parameters. We expressed E using the simplified Penman–Monteith equation and modeled canopy conductance ( G c ) as a product of reference G c ( G cref ) when vapor pressure deficit is 1.0 kPa and functions expressing the responses of G c to meteorological factors. We determined G cref and parameters of the functions for the sites separately. E observed for the 14 sites was not reproduced well by the model when using mean values of G cref and the parameters among the sites. However, E observed for the sites was reproduced well when using G cref determined for each site and mean values of the parameters of the functions among the sites, similar to the case when using G cref and the parameters of the functions determined for each site. These results suggest that considering variations in G cref among the sites was important to reproduce variations in E , but considering variations in the parameters of the functions was not. Our analysis revealed that G cref linearly related with the sapwood area on a stand scale ( A ) and that A linearly related with stem density ( N ) and powers of the mean stem diameter ( d m ). Thus, we proposed a model relating E with A (or N and d m ), where G cref was calculated from A (or N and d m ) and the parameters of the functions were assumed to be the mean values among the sites. This model estimates changes in E with changing structure from commonly available data ( N and d m ), and therefore helps improve our understanding of the underlying processes of the changes in the water balance for Japanese cedar and cypress plantations. [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]

The article discusses a study which examines how whole-tree transpiration can be computed from the base of the stem in the Japanese cedar and cypress trees using of sap flow and stem water content measurements and a whole-tree water balance equation. The study measured sap flows at the base of the stem and upper trunk and stem water contents at vertical positions on the trunk using of sensors. It concluded that further study is needed into the effects of tree sizes and soil moisture conditions.

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]

Tree root system development alters forest soil properties, and differences in root diameter frequency and root length per soil volume reflect differences in root system function. In this study, the relationship between vertical distribution of very fine root and soil water content was investigated in intact tree and cut tree areas. The vertical distribution of root density with different diameter classes (very fine <0.5 mm and fine 0.5–2.0 mm) and soil water content were examined along a slope with two coniferous tree species, Cryptomeria japonica (L.f.) D. Don and Chamaecyparis obtusa (Siebold et Zucc.) Endl. The root biomass and length density of very fine roots at soil depth of 0–5 cm were higher in the Ch. obtusa intact tree plot than in the Cr. japonica intact plot. Tree cutting caused a reduction in the biomass and length of very fine roots at 0–5 cm soil depth, and an increment in soil water content at 5–30 cm soil depth of the Ch. obtusa cut tree plot one year after cutting. However, very fine root density of the Cr. japonica intact tree plot was quite low and the soil water content in post-harvest areas did not change. The increase in soil water content at 5–30 cm soil depth of the Ch. obtusa cut tree plot could be caused by the decrease in very fine roots at 0–5 cm soil depth. These results suggest that the distribution of soil water content was changed after tree cutting of Ch. obtusa by the channels generated by the decay of very fine roots. It was also shown that differences in root system characteristics among different tree species affect soil water properties after cutting. [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]

Soil water repellency (SWR) is a cause of low water infiltration, overland flow and soil erosion in mountainous coniferous plantations in Japan. The factors determining SWR intensity were investigated in two coniferous plantations of Chamaecyparis obtusa (Siebold et Zucc.) Endl. and Cryptomeria japonica (L.f.) D. Don, using intact tree plots and cut tree plots on the same hillslope. The SWR of Ch. obtusa plots was stronger than that of Cr. japonica plots. SWR intensity decreased after tree cutting. There were no significant differences in SWR upslope and downslope of individual trees/stumps for both tree species, though areas downslope of individual Ch. obtusa trees had higher SWR intensity than those upslope. SWR intensity and soil aggregate stability were positively correlated in the Ch. obtusa intact tree plot (r = 0.88, p < 0.01), whereas in the cut tree plot, this correlation was weak with no significance (r = 0.29, p = 0.41). Soil aggregate size had a non-significant influence on SWR intensity. These findings suggest that SWR intensity was not related to the soil aggregate size, but SWR intensity seemed have a role in soil aggregation in the Ch. obtusa intact tree plot. Destruction of soil aggregates could occur after tree cutting because of physical disturbances or increased input of different types of organic matter from other vegetation into soil. The presence of Ch. obtusa introduces a source of SWR, although uncertainty remains about how water repellency is distributed around soil aggregates. The distribution pattern of soil water content and soil hydraulic conductivity around Cr. japonica was related to other factors such as the litter layer and non-water-repellant soil. [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]

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]