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The large-scale expansion of Moso bamboo forests in Japan raises concerns about how vegetation will affect the hydrological cycle and local water resources. However, information on transpiration (E) is limited to study on a single bamboo stand with low culm density (4 000 ha-1). The present study conducted a year-round measurement of E in a high-density (11 000 ha-1) stand using sap-flow measurements, and additional measurements were made during summer in the previously studied low-density stand and a neighbouring Japanese cedar stand for comparison. Annual E of the high-density stand was estimated at 455 mm. Although the value was greater than those reported for neighbouring coniferous forests (250-370 mm), it was lower than previous measurements made in the low-density stand (567 mm). The daytime sap flux density of the high-density stand was generally less than half that in the low-density stand, resulting in similar daily maximum E values in those stands. In addition, E typically peaked before midday in the high-density stand followed by a rapid decline; the midday suppression of E led to decreased total E in the stand. Based on present and previous measurements of E, combined with the lower rainfall interception (I) reported for bamboo stands, water loss through evapotranspiration would be comparable between bamboo and coniferous forests. Present results also suggest that the E of bamboo stands does not have strong positive relationships with stand structural parameters (e.g., culm density and sapwood area) but possibly depends more on the sites' microenvironments (e.g., solar radiation). [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]

The article presents a study which examines the wet-canopy evaporation process within the forest canopy. It states that this process has been applied on eleven individual tress of various heights, ranging from two to fifty meters in Bornean tropical rainforests. It notes the area and structure of the forest, the sap flow and the meteorological measure. It also presents that the length of the canopy drying time after rainfall appears to be strongly related to meteorological conditions above and within the canopy.

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]

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]

Abstract: This study was undertaken to quantify interannual variations of total evaporation (ET) in a tropical rainforest in Sarawak, Malaysia. To this end, we conducted 10-year meteorological measurements and formulated a simplified big-leaf model that reproduces transpiration (Et), rainfall interception (Ei), and ET as the sum of these. The model was validated independently using eddy covariance fluxes, rainfall interception based on throughfall and stemflow measurements, and sap flow measurements conducted for more than 2 years. Using the model, Et, Ei, and ET were estimated for the period 2000–2009. Annual Et, Ei, and ET averaged over 10 years were estimated as 1114, 209, and 1323mm, respectively, with small seasonal fluctuations. The derived estimates showed conservative year-to-year variations in annual Et, Ei, and ET (CV=5–7%) in contrast to considerable year-to-year variations in annual rainfall (CV=11%). Specific rainfall characteristics (e.g. intense short duration storms) at this site can explain the conservative year-to-year Ei variations. Small interannual variations in meteorological conditions and absence of severe drought during the study period can explain the small year-to-year Et variations. To characterize ET at our site, we also compared Ei and ET at our site with those of other tropical forests. Based on the derived ET characteristics, we discuss possible ET changes in response to changes in rainfall regime at this site. [Copyright &y& Elsevier]