Confocal laser scanning microscopy (CLSM) was applied as a new method of visualizing the shrinkage of wood and its anisotropy. Control of relative humidity and temperature in a specialized environment chamber made it possible to acquire transverse images of tracheids of Akamatsu (Pinus densiflora) from the saturated condition to the dried condition. The shrinkage of tracheid cells was also determined by measuring the tangential diameter of tracheid and lumen, the radial diameter of tracheid and lumen, and the thickness of tangential and radial walls. Moreover, this technique makes it possible to discuss the relationship between moisture content and tracheid cell shape. We found the CLSM technique to be an effective method for visualizing shrinkage of tracheid cells with desorption.
The microcracks occurring during drying of wood were visualized under confocal laser scanning microscopy (CLSM). Precise control of relative humidity and temperature in a specialized environment chamber made it possible to acquire sequential images of the wood of Cryptomeria japonica during drying from the water-saturated condition. The images indicated that the microcracks occurred between tracheid and ray parenchyma in the latewood region and the crack tip advanced in both the bark and pith directions. Subsequently, the crack tip expanding towards the bark stopped at the earlywood region through the growth ring boundary. The other tip toward the pith stopped at the earlywood region before reaching the growth ring boundary. Our technique made it possible to generate microcracks and discuss the relationship between moisture content and microcrack formation during drying. We found the CLSM technique to be an effective method for visualizing microcrack propagation with time.
Growth ring structure and wood density were compared among five families of Pinus patula planted in Malawi, Africa. The vertical and radial variations of wood density and growth characteristics were investigated in stems of 30-year-old Pinus patula planted at a spacing of 2.74 × 2.74 m. The pattern of ring width with cambial aging was broadly similar at all stem heights: wide to the 4th growth ring, decreasing gradually up to the 10th ring and then very narrow towards the bark. In all the families, the first complete growth ring was the widest, ranging from 20 to 50 mm across the families. This trend was different from other similar studies carried out in Zimbabwe and South Africa where the growth ring width increased from the 1st to the 3rd ring with the highest ring width of 19 mm. Specific gravity varied with height above the ground for all the trees. The average specific gravity was 0.56. Weak to medium correlations between latewood percentage and specific gravity were observed. The study shows that selection for density in Pinus patula could be made at least by the age of 10 years.