Genetic Variation of Wood Specific Gravity and Tracheid Length of Open-Pollinated Progeny Families in Calocedrus formosana

A test plantation containing 5o wind-pollinated progeny families representing 3 provenances of Taiwan incense cedar (Calocedrus formosana) was established in central Taiwan in 1976. A randomized complete block design was adopted in the field layout with 7-tree linear plots in each of 4 replications and a 2 x 2-m spacing between plants. At a tree age of 27 yr, a 10-mm caliber increment core sample was extracted at breast height in the east cardinal direction from the mid-DBH size tree per plot. Thirty families (out of 50) with 100% survival of trees in each of 4 replications were selected for increment-core extraction. In total, 120 cores (1 core family-1 plot-1 x 30 families x 4 replications) were sampled. From each core, only the 6 outermost growth rings near the bark were used to assess the specific gravity and tracheid length. Variations among provenances and among families within a provenance were analyzed using a general linear model. No significant difference among provenances was found in either trait. Significant variations among families within provenances were detected at the 5% level for specific gravity but not for tracheid length. Tree-to-tree variations in both traits accounted for more than 80% of the total variances. The overall mean values were respectively 0.494 for wood specific gravity and 3.16 mm for tracheid length. The family heritability estimate for tracheid length was 0.296, which was weaker than that for wood specific gravity (0.412). Therefore, different strategies of future selection programs are discussed.