Juichi Tsutsumi

Effect of thinning on the wood structure in annual growth rings of Japanese larch (Larix leptolepis) by

The objective of this study was to determine the effect of thinning on the annual ring structure and the cross-sectional dimensions of tracheids in plantation-grown Japanese larch (Larix leptolepis). Annual ring width, earlywood width and latewood width increased significantly after thinning. The width of the band of nonflat latewood tracheids in the annual ring increased more than that of flat latewood tracheids. Thinning did not significantly affect latewood percentage. The average radial diameter of both earlywood and latewood tracheids increased after thinning. After thinning, average wall thickness of earlywood tracheids increased, while that of latewood tracheids decreased. Cell wall percentage in earlywood was not influenced significantly by thinning, but latewood cell wall percentage decreased. The changes of the average radial tracheid diameter, the average wall thickness of tracheids and cell wall percentage from earlywood to latewood within a growth ring became more gradual after thinning. However, thinning did not affect significantly the cell wall percentage of the whole growth ring. This study suggests that thinning has little effect on wood density of the whole growth ring in Japanese larch.

Relationship between Wood Anatomical Properties and Specific Permeability of Sugi (Cryptomeria japonica) Sapwood and Intermediate Wood

The objective of this study was to clarify anatomical factors which determine specific permeability of sapwood and intermediate wood in air-dried sugi (Cr?~ptomeria juponica) wood. Superficial air permeability of sugi sapwood and intermediate wood was measured and then specific permeability was determined. Using these specimens for permeability tests, the proportion of latewood and earlywood, the percentage ol aspirated and incompletely aspirated pits, the number of bordered pits per tracheid, the number of tracheids per unit area and tracheid length were obtained. Specific permeability decreased with increasing levels in the stcm except for the lowest level and also related to distance from pith, suggesting that cambial age is related to specific permeability. A clear relationship between percentage ol latewood and specific permeability was not found, suggesting that effective pathways in earlywood determines permeability. Specific permeability of intermediate wood and sapwood were significantly related to the number of effective open pits in earlywood, Mi3J, which was determined by anatomical properties such as aspirated and incompletely aspirated pits, the number of pits and tracheids, and proportion of latewood, suggesting that specilic permeability of sugi sapwood and intermediate wood is a physical value determined by the intrinsic properties of earlywood in addition to the condition of bordercd pits.