Search

To estimate whole-tree or stand transpiration based on sap flow measurements, sap flux density (Fd) needs to be scaled up over the entire sapwood area. We investigated radial variations in Fd in the dominant oak (Quercus liaotungensis) and a commonly occurring oriental arborvitae (Platycladus orientalis) species using Granier-type thermal dissipation probes in a semi-arid forest in northern China. Our results show that Fd in oak trees reached a maximum just below the cambium and decreased towards the inner sapwood. On the other hand, radial sap flow patterns in oriental arborvitae trees differed among individuals. Fd values at different depths within an individual were highly correlated with each other in both species. We assessed the error of single-depth measurements when upscaling to whole-tree water use using multi-depth measurements as a reference. Omitting radial variations resulted in an overestimation of daily water use by 38% and 78% in oak trees with sapwood depths of approximately 2 and 3 cm, respectively. The outer sapwood annuli (0-1 cm) contributed 74% and 65% to the total water use in the two classes of sapwood depth. These contribution coefficients may be used as correction indices for estimating whole-tree water use. Errors of omitting radial variations in oriental arborvitae trees ranged from 42% to 21%. Using relatively long sensors (e.g. 2 cm) may improve the estimate accuracy in this species. The results would be applicable to the estimation of tree or stand transpiration based on routine depth measurements using one set of sensors. It is suggested that radial variations should be considered for accurately upscaling locally measured sap flow data to whole-tree water use in trees with wide sapwood and that different approaches may be applied to species with different patterns of radial variations. [ABSTRACT FROM AUTHOR]

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]

In this study, we aimed to clarify spatial variations in xylem sap flow, and to determine the impacts of these variations on stand-scale transpiration ( E) estimates. We examined circumferential and radial variations in sap flow velocity ( F d) measured at several directions and depths in tree trunks of black locust ( Robinia pseudoacacia) and native oak ( Quercus liaotungensis), both of which have ring-porous wood anatomy, in forest stands on the Loess Plateau, China. We evaluated the impacts of circumferential variations in F d on stand-scale transpiration estimates using a simple scaling exercise. We found significant circumferential variations in F d in the outermost xylem in both species (coefficients of variation = 20-45%). For both species, F d measured at the inner xylem was smaller than that of the outermost xylem and the F d at the depth of > 10 mm was almost zero. The simple exercises showed that omitting circumferential variations in F d affected the E estimate by 16-21%, which was less than the effects of omitting within-tree radial and tree-to-tree variations in F d in both species. These results suggest that circumferential variations in F d can be a minor source of error for E estimates compared with within-tree radial and tree-to-tree variations in F d, regardless of the significant circumferential variations. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

According to widely held belief, annual evapotranspiration (ET) for broadleaf forests is less than that for coniferous forests, resulting in higher annual runoff for broadleaf forests. We processed 82 catchment runoff and 126 interception loss data from temperate regions and found that although the belief is valid under conditions of broadleaf deciduous forests and high winter precipitation (e.g. the United States), it is invalid under conditions of broadleaf evergreen forests (e.g. New Zealand) or low winter precipitation (e.g. Japan). Thus, forest management policies based on this belief should be reconsidered on the basis of our results for regions with broadleaf evergreen forests or low winter precipitation. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents a study of storm flow samplings and discrete interval samplings of stream water to examine the effects of storm flow samplings on the evaluation of Dissolved Inorganic Nitrogen (DIN) and sulfate. The result of discrete interval sampling indicated that the relationships of DIN concentration to the discharge amount found in the stream water differed from the storm flow sampling. The outcomes confirmed that storm flow samplings are important for estimating annual exports.