Characteristics of the annual ring structure related to wood density variation in sugi (Cryptomeria japonica)

The effects of annual ring structural factors on the variation in wood density in sugi (Criptomeria japonica D. Don) from different sources were examined by means of multiple regression analysis within the annual ring width limit of 1 to 5 mm. It was concluded that the percentage of latewood was commonly the most important factor for wood density in this species, although other factors such as early- and latewood densities also were related. The variability in the percentage of latewood was a characteristic corresponding to increases of ring width. The latewood percentage decreased entirely with increased ring width, but patterns of the variation were different within each sugi-producing district. The variability in the percentage of latewood is fundamentally summarized into several types, and these types appear to be closely associated with quantitative patterns of latewood formation. It is explained that the quantitative difference of variability in latewood width is related closely to patterns in the tracheid flattening of radial diameters. Therefore, this suggests that the flattening patterns of tracheid are related closely to the variability in wood density, and that these patterns must be affected by some growth conditions.