Kotaro Sakuta

Distribution of hydraulic resistance in seedlings, sprouts and an adult tree of Pasania edulis Makino

Hydraulic resistance is an important factor in predicting water status. Hydraulic resistance of petiols, stems and branches, and roots was measured inPasania edulis Makino in order to compare the distribution of resistance between current seedlings, current stump sprouts and a 16 year old adult tree. Total resistance showed only minor variations despite large variations in plant size. This result is thought to be consistent with allometry between leaf mass and supportive organ mass, and with changes in permeability of conductive organs. Root resistance was low in sprouts and the adult tree due to their mature root systems. Current seedlings with undeveloped root systems had high root resistance. The proportion of petiol resistance in total resistance was high compared to the proportion of their conductive distance, and was thought to be a limiting factor of tree water status. The petiol resistance of the adult tree leaves was higher than for seedling and sprout leaves. From a comparison with the leaf water relation characteristics, the petiol resistance was thought to be provided as low values for intolerant leaves against water stress in order to compensate water inflow, and high values for tolerant leaves to regulate water inflow.

Construction of one-way volume table for the three major useful bamboos in Japan

The one-way volume table for the three major useful bamboos in Japan, i.e., Phyllostachys pubescens Mazel ex Houz., Phyllostachys bambusoides Sieb. et Zucc. and Phyllostachys nigra var. henonis, was constructed based on a dataset of 920 felled culms collected from five different districts. Twenty-three models were fitted to the height–diameter relationship for each species, and their goodness of fit were compared. The height–diameter relationship for P. pubescens and P. nigra could be expressed by the reciprocal equation, whereas that for P. bambusoides was approximated by the simple allometric power equation. The culm height was predicted by substituting the measured diameter at breast height (dbh) into the determined height–diameter model. The apparent culm volume was then estimated from the measured dbh and the predicted culm height with the two-way volume equations derived in previous studies. For all species, there was no significant difference between the actual and estimated apparent culm volume. The one-way volume table for these bamboo species was constructed by combining the two-way volume equation and the height–diameter model, so that the apparent culm volume could be solely estimated from dbh. For the same dbh, P. bambusoides had the largest apparent culm volume compared to the other two species, whereas P. pubescens had the smallest one. The difference in the apparent culm volume was caused by the inter-specific variations in culm slenderness and/or taper. The volume table developed here will be useful in evaluating the amounts of resources of the three major useful bamboos in Japan.

Effects of light and microsite conditions on tree size of 6-year-old Cryptomeria japonica planted in a group selection opening

We examined the extent to which direct and indirect measures of light and microsite conditions could explain variation in tree height and diameter at the base of 6-year-old Cryptomeria japonica trees planted in a group selection opening of about 0.32 ha on a steep slope at Shiiba, Miyazaki Prefecture, southern Japan. We first used the gap light index (GLI) and soil thickness (ST) as directly measured indices. For an indirect measure of light, we used a between-cohort competition index (BCI) estimated from the position and total height of residual trees. For indirect measures of microsite, we examined topographic indices (slope, plan and profile curvature, average slope gradient, and relative elevation) derived from digital elevation models (DEMs) with different resolutions ranging from 2 to 10 m. The multiple linear regression using GLI and ST explained about 45% of variation in tree size, while simple regression using only GLI explained about 35%. The contribution of ST was about half of GLI. The multiple regressions using BCI and the topographic indices did not explain any more variation than using BCI alone (R2 of about 0.26). We conclude that microsite conditions with shallower soil and steeper slope have negative effects on tree growth in group selection openings, although the relative importance is smaller than light conditions. More comprehensive studies considering several openings with more heterogeneous topography including different species are needed to generalize our growth prediction using the indirect measures, which are useful for practical forest management.

Effects of topography and planted trees on the distribution of naturally regenerated broad-leaved trees in a 140-year-old Cryptomeria japonica plantation in northern Kyushu, Japan

We investigated factors affecting the distribution of naturally regenerated broad-leaved trees in a 140-year-old Cryptomeria japonica plantation. We used path analysis to examine the relationship among microtopography, the biomass of planted trees, and the biomasses of canopy and subcanopy trees of broad-leaved species. The study plot was divided into three topographic types (ridge, slope, and valley), and we discuss how the different topographic types are affected. For all topographic types, the biomass of canopy trees of broad-leaved species decreased with convexity. For slope and valley topographies, the biomass of subcanopy trees of broad-leaved species also decreased with convexity. For ridge topography, the biomass of subcanopy trees of broad-leaved species increased with the biomass of planted trees, and decreased with the biomass of canopy trees of broad-leaved species. These results suggest the effects of microtopography on the biomass of subcanopy trees were much larger than the effects of canopy trees for slope and valley topographies, while the effects of microtopography were smaller for ridge topography.

Differences in growth responses between Cryptomeria japonica and Chamaecyparis obtusa planted in group selection openings in Kyushu, southern Japan

ABSTRACT We quantified the differences in growth responses between Cryptomeria japonica and Chamaecyparis obtusa trees in approximately 0.1-ha group selection openings in southern Japan. We measured the position, height (H), and diameter at ground level (D) of 6- and 13-year-old C. japonica and C. obtusa trees that were planted in two respective openings. The annual H and D growth of C. japonica increased until trees were 10 and 8 m, respectively, distant from the nearest edge of the opening. For C. obtusa, the annual H and D growth increased slightly until the trees were 6 m distant from the nearest edge, but they did not significantly differ between 6 and 18 m distant from the nearest edge. While the shortest distance from the edge explained 63% and 50% of the variationsal H and D growth, respectively, of C. obtusa. Our result demonstrates that C. obtusa is less sensitive to edge effects than C. japonica. We conclude that C. obtusa is likely to be more suitable than C. japonica for planting within 0.1-ha group openings, as it will result in faster early stage growth, with less variation, within the openings.