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

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]

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]

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: Sap flow velocities in stems (Sfs) were measured in four 50-m tall emergent trees in a Bornean tropical rainforest. Cross-correlation analysis was used to estimate time lags between diurnal patterns of Sfs and canopy-scale transpiration (Tr) calculated from a big-leaf model validated by water-vapor flux measurements at this site. The time lags between Sfs and Tr were found to be less than 20min in these trees in both wet and medium dry conditions. In addition, the time lags between Sfs and sap flow velocities measured in a branch at the top of an emergent tree were also less than 20min. These results are in contrast to those of previous studies conducted in a neo-tropical forest ecosystem, which reported significant time lags of 40–120min between transpiration and stem sap flow in emergent trees. The results of this study suggest that hydraulic resistance along the conductive pathway and internal water storage between tree crown and stem are insignificant for this forest. Our results also suggest that sap flow measurements conducted at accessible points can be used to estimate canopy transpiration on a diurnal time scale without accounting for the time lags between canopy transpiration and stem sap flows, despite the 50-m tall forest canopy at our site. [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]

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]

Previous studies reported relationships between stem diameter at breast height (DBH) and whole‐tree transpiration (Qt) across a variety of species and locations. It might be possible to develop a relationship between DBH and Qt with smaller variations when we focused on a single species. We attempted to develop such a relationship for Japanese cypress (Chamaecyparis obtusa), which is one of the major plantation species in Japan. We collated Qt for 51 Japanese cypress trees from nine different‐sized and different‐aged stands using the sap flux method. We found a strong linear correlation between DBH and the reference value of Qt at a vapour pressure deficit of 1 kPa (R = .883). This was a consequence of a strong correlation between DBH and sapwood area (AS_tree; R = .973) and the absence of a correlation between DBH and sap flux density (R = −.043). We confirmed that using the relationship between DBH and AS_tree, while assuming typical responses of sap flux density to meteorological factors, provides reasonable Qt estimates. This study also demonstrated how the DBH–Qt relationship can be applied to estimate changes in EC with changing forest management. [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]