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Bamboo forests have been expanding rapidly in Asian countries for the past 50 years. Whether natural or artificial, this expansion involves the replacement of other vegetation types by bamboo, which could impact the local water cycle. Previous studies in Japan have reported that bamboo forests have higher transpiration than coniferous forests under temperate climates, but it is unknown whether this finding applies to subtropical climates. Thus, we examined whether a Moso bamboo ( Phyllostachys pubescens) forest exhibits higher transpiration in a subtropical climate. We used the sap-flux method to estimate the stand transpiration ( E) of Moso bamboo and Japanese cedar ( Cryptomeria japonica) forests in Taiwan. As was observed in the Japanese studies, annual E for bamboo (478 mm) was higher than that for cedar (122 mm), although we found a difference in the seasonality of E between the Taiwanese and Japanese sites. Canopy conductance ( Gc) for bamboo was higher than that for cedar in Taiwan, which was reported previously for Japan. Gc for bamboo in Taiwan was comparable to that in Japan, despite a difference in the leaf area index (LAI). Gc for cedar in Taiwan was lower than that in Japan. This difference in Gc between Taiwan and Japan corresponded to differences in the sapwood area and LAI. These findings suggest a significant change in E and, therefore, the terrestrial water and carbon cycle, regardless of different climates, when Japanese cedar forests are replaced by Moso bamboo forests. [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 the sapwood area at stand scale ( A) is an important factor determining changes in transpiration by canopy trees ( E). This study examined changes in A for four to six years after thinning of two Japanese cedar and two cypress plantation sites, each having three or four plots with different thinning intensities and one control plot. We focused on whether there was a difference in A (δ A) between a thinned plot and a control plot during the experimental period. We observed increased radial stem growth for plots with low stem density ( N) due to intensive thinning. However, δ A did not decrease to zero during the experimental period for any plot. The increased radial stem growth was not large enough to cancel the effect of low N due to thinning. These results imply that a lower E for thinned plantations as compared to non-thinned plantationsis remains for several years (more than 10 years, according to our results) after thinning and that thinning could be an effective method of reducing water consumption by canopy trees. [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]

To our knowledge, no one has examined the canopy conductance of a Cryptomeria japonica plantation, although such forests are very common in Japan. We plan to examine the canopy conductance of a Cryptomeria japonica plantation (canopy height 8 m) based on 1-year sap-flow data using the simplified Penman-Monteith equation. This study examines the effect of the aerodynamic control of transpiration before calculating canopy conductance using the simplified Penman-Monteith equation, because the equation assumes that the effect of aerodynamic control is negligible. To examine the effect of aerodynamic control, we examined the dependency of the relationship between the vapour pressure deficit (VPD) and transpiration on wind speed, when solar radiation, air temperature, and soil water content do not limit transpiration greatly. The relationship between VPD and the heat pulse velocity measured 11 m above the ground was dependent on wind speed only when the wind speed was < 0.7 m s-1. This suggests that the effect of aerodynamic control was negligible when the wind speed was < 0.7 m s-1, but that the effect was not negligible when the wind speed was < 0.7 m s-1. Therefore, we should use data from when the wind speed was ≥ 0.7 m s-1 for calculating canopy conductance Gc, based on the simplified Penman-Monteith equation. Although this criterion is site specific, the methods used to develop it are applicable to other sites. [ABSTRACT FROM AUTHOR]

To our knowledge, there is no information on the canopy conductance of Cryptomeria japonica plantations, although such forests are very common in Japan. We examined the canopy conductance Gc of a C. japonica plantation based on 1-year sap-flow data using the simplified Penman-Monteith equation. After selecting data based on the criterion proposed in part 1 of this study (Komatsu et al., 2006. Hydrological Processes 20: this issue), we now examine Gc responses to meteorological factors. Gc was expressed using functions of solar radiation S (W m-2), the vapour pressure deficit D (kPa), and air temperature T (°C). The resulting functions were f1(S) = [(1000 + 30)S]/[1000(S + 30)], f2(D) = exp(-0.54D)/exp(-0.54), and f3(T) = {[(30 - 5) + 14](T - 5)}/{(30 - 5)[(T - 5) + 14]), where f1(S), f2(D), and f3(T) are functions expressing the Gc responses to S, D, and T respectively. The functions were characterized by comparing general functions for coniferous forests, which showed that it was necessary to consider f3(T) to reproduce the 1-year transpiration at the site, and that f1(S) and f2(D) determined here were not very different from the general functions. This paper is the first to determine Gc responses to meteorological factors for a C. japonica plantation. When predicting transpiration from a C. japonica plantation using hydrological or ecological models, the functions determined here should be used instead of the default functions of the models. [ABSTRACT FROM AUTHOR]

• We developed a model tool to assist forest and water-resource policymaking. • The model focuses on two major plantation species in Japan. • The model can compare available water resources for different management scenarios. • The model can assess effectiveness of existing policy recommendations. • The study inspires development of similar models for other species/regions. Examining changes in evapotranspiration with forest management is one starting point for comprehensively understanding the impacts of forest management on water resources and forest resilience. This study builds on our previous work and develops a practical model that predicts changes in evapotranspiration with the management of Japanese cedar and cypress plantations. The model has distinct features that it requires only stem density, mean diameter at breast height, and basic meteorological data as inputs. This study first confirms that the model predicts annual evapotranspiration for cedar and cypress with relatively small errors (approximately 60 mm at the maximum). Next, this study shows that the model predicts changes in annual evapotranspiration with thinning and clearcutting of cedar and cypress with small errors (the mean absolute error of 86 mm). This study then demonstrates that coupling the model and yield tables enables prediction of annual evapotranspiration for different management scenarios and then the assessment of policy recommendations. Indeed, our model prediction suggests that the decrease in annual evapotranspiration with cedar and cypress aging is seemingly much smaller than that assumed in existing policy recommendations. Our model also suggests that the decrease in annual evapotranspiration with aging can more than triple by thinning at a rate of 50%, although this suggestion should be tested by future observation studies. The model is applicable only to Japanese cedar and cypress plantations under Japan's meteorological conditions, but similar models for other mono-specific plantations can be developed. This study will thus inspire forest scientists to develop models that assist policymaking for other species in other areas. [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]

Highlights: [•] We obtained reliable estimations of water use components in Japanese cedar stands. [•] We found a constant ratio of interception to rainfall (P) throughout a year. [•] Upper canopy transpiration contributes to total water use during scarce rainfall. [•] These result in a conservative ratio of evapotranspiration to P throughout the year. [ABSTRACT FROM AUTHOR]