Ring characteristics and screw withdrawal resistance of naturally regenerated Chamaecyparis obtusa var. formosana trees

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The ring characteristics and screw withdrawal resistance (SWR) of naturally regenerated Taiwan yellow cypress (Chamaecyparis obtusa var. formosana) trees were explored. Significant differences in average ring width (RW), earlywood width, latewood width, ring density (RD), earlywood density (ED), latewood density (LD), highest density (Dmax), lowest density (Dmin), latewood percentage (LWP), and SWR were observed between trees, rings (SWR excluded), and tree height positions. The RW components in the radial direction increased from the pith outward to about the 3rd to 5th ring and then decreased to about the 25th ring; it was almost constantly sustained toward the bark side. The RD in the radial direction slowly decreased from the pith outward to the bark side. Average ring width and ring density were significantly affected by the various tree growth rates, radial ring numbers, and tree height positions. ED, LD, Dmax, Dmin, and LWP were the most important factors determining the overall RD. RW did not correlate with tree RD. SWR is correlated with ED, RD, Dmin, LWP, and intra-ring density variation (IDV). Thus, the SWR can be used to predict wood density and in nondestructive evaluation of a living tree.