Yasuki Shiiba

Spatial variations in xylem sap flux density in evergreen oak trees with radial-porous wood: Comparisons with anatomical observations

To estimate whole-tree water use when employing sap flow measurements, integration of the sap flux density (Fd) over the sapwood area is needed. Accordingly, it is necessary to obtain information on the characteristics of stem water transportation such as spatial variations in Fd and the active xylem area in the stem cross-section. Although evergreen oak trees with radial-porous wood represent a major component of secondary forests in western Japan, detailed information on their stem water transportation characteristics remains unclear. In the present study, we used the heat dissipation method (Granier method) to conduct measurements of azimuthal and radial variations in the Fd of Quercus glauca Thunb. ex Murray, a representative evergreen broad-leaved tree in western Japan. Further, by analyzing the anatomy of the xylem structure, we examined why Fd varies spatially in the stem cross-section. By using a dye solution injected into a radial hole bored into the tree trunk, we confirmed that the entire stem is hydroactive. We also compared the spatial variations in Fd and water conductivity per xylem area (Ks) which were estimated by using the observed vessel diameters and their density over the stem cross-section and Hagen–Poiseuille’s law. Azimuthal and radial variations in Fd reached about 60 and 50% of the maximum values, respectively, and could be explained by spatial variation in Ks. As a result, we obtained statistical parameters describing the spatial variation in Fd in Q. glauca and determined that whole-tree water use estimated from measurements in one direction had at most ±20% potential errors for studied trees.

Green moisture content and basic density of 95 woody species growing in Kyushu University Forests, Japan

We investigated the green moisture content and basic density of 95 woody species growing in Kyushu University Forests. In softwood species, the green moisture content of heartwood ranged from 28% in Cryptomeria japonica to 67% in Abies firma, and in sapwood, from 75% in Tsuga sieboldii to 160% in Cryptomeria japonica. The green moisture content of softwood trees was greater in sapwood than heartwood. The green moisture content in the heartwood of hardwood species ranged from 34% in Euonymus alatus f. striatus to 83% in Kalopanax pictus, and in sapwood, from 45% in Fraxinus sieboldiana to 153% in Actinidia polygama. We found three radial variation pattern types in stems of hardwood species. The green moisture content was higher in heartwood than sapwood, in the first type, whereas in the second, it was higher in sapwood than heartwood. In a third type, differences between heartwood and sapwood were relatively small. The basic density of softwood species ranged from 378 kg/m3 in Cryptomeria japonica to 524 kg/m3 in Tsuga sieboldii. Most trees tended to decrease in basic density from corewood to outerwood. Basic density in hardwood species ranged from 266 kg/m3 in Paulownia tomentosa to 751 kg/m3 in Rhaphiolepis indica var. umbellata. We identified three types of radial variation pattern in stems of hardwood species. In the first type, basic density was higher in corewood than outerwood, whereas in second, it was higher in outerwood. In the third type, differences between corewood and outerwood were small. We also provided the information on the age and size of heartwood formation. Keyword:green moisture content; basic density; Kyushu University Forests; Japan