Effects of plantation spacings on the quality of visually graded lumber and mechanical properties of Taiwan-grown Japanese cedar.
Effects of plantation spacings on the log and lumber grades and the bending strength of 41-year-old Taiwan-grown Japanese cedar (Cryptomeria japonica) were investigated. Five plantation spacings and the number of trees per hectare used in this experiment were 1×1 m (Type A: 10,000 trees/ha), 2×2 m (Type B: 2,500 trees/ha), 3×3 m (Type C: 1,110 trees/ha), 4×4 m (Type D: 630 trees/ha), and 5×5 m (Type E: 400 trees/ha). Results indicated that the greatest frequencies of first grade logs, special and first grade lumber, largest values of specific gravity in air-dried conditions, and dynamic modulus of elasticity (ED), static bending modulus of elasticity (MOE), and modulus of rupture (MOR) occurred in trees obtained from the Type A plantation spacing, but the smallest ones were in those cut from the group of Type E. Large significant differences occurred between these two types (A and E). However, significant differences among the other three types (B, C, and D) were not observed. The average values of ED, MOE, and MOR of visually graded special grade lumber were significantly greater than those of the second and third grade groups.