This study assessed the effect of the change in forest structure including understory vegetation of Sasa nipponica on soil C and N accumulation from 0 to 40-yr Japanese oak ( Quercus crispula ) plantation chronosequence. The peak of understory biomass was at 7 years after afforestation. Biomass of the overstory species linearly increased, and the biomass of overstory species was more than that of understory species after 8-yr. According to leaf mass index change along with stand age, canopy closure was occurred about 12 years after afforestation. The ranges of temporal changes in both soil C and N accumulations increased from surface to deep soil layers. The changes in C and N accumulation of O layer were large during early stage of stand development, and C and N accumulations increased until 10 years and 20 years after afforestation, respectively. Overstory leaf mass positively correlated with C and N accumulations in O layer. Understory biomass negatively correlated with N accumulation in O layer and positively correlated with C/N ratio. The N accumulations both in mineral soil 0-4 and 4-8cm in depth were negatively correlated with fine root mass of S. nipponica . The results suggested that change in vegetation structure such as canopy closure by overstory and dynamics of understory biomass affected soil C and N accumulations.

The relationships between habitat partitioning and the pattems of species diversity of collembolan families in relation to horizontal and to soil depth distributions have not been understood yet. The relationships between soil depth distribution a d alpha diversity within a forest stand or beta diversity among forest stands in Simpson's diversity index for 9 family groups of soil Collembola were studied in 6 natural broad-leaved forests and 5 larch plantations of cool temperate zone in northern Japan. Studied forests were on wide range of environrriental gradients including two forest types, deciduous broad-leaved natural forests and larch plantation, on south and north facing slopes, and from upper ridge to bottom of the slopes. Collembolan species were classified into 9 family groups. The percentages of organic layer dwellers to total abundance for a family group (%OL) of Tomoceridae, Entomobryidae, Neelidae and Sminthroidea were significantly higher than the other families. The standard deviation of weighted mean of %OL (SDW) of Isotomidae and Onychiuridae!Tullbergiidae were significantly higher than the other families, uggesting that Isotomidae and Onychiuridae/Tullbergiidae should have the widest range ofhabitat in soil depth distribution. Based on Simpson's D, alpha diversities of Isotomidae and that of OnychiuridaelTullbergiidae were high, whereas those of Hypogastruridae and of Oncopoduridae were low. Beta diversities of Hypogastruridae and Tomoceridae were high, whereas those of Isotomidae and of OncopoduridaerTullbergiidae w re low. The significant positive correlation between the SDW and alpha diversity and between SDW and contribution ofalpha diversity to garnma diversity of family groups were fbund, indicating that the range of soil depth distribution among species within a family related with local diversity of collembolan family, The %OL and beta cliyersity were not significantly correlated. Negative correlation between alpha and beta diversities of family groups was found. indicating that families with high local diversity within a forest stand had low tumover diversity among forest stands in this site.

To estimate whole-tree water use when employing sap flow measurements, integration of the sap flux density (F d) 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 F d 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 F d 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 F d 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 F d and water conductivity per xylem area (K s) 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 F d reached about 60 and 50% of the maximum values, respectively, and could be explained by spatial variation in K s. As a result, we obtained statistical parameters describing the spatial variation in F d 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.