Comparisons of tracheid lengths in Pinus densiflora Siebold & Zucc.: earlywood versus latewood and province versus province

The tracheid length (TL) in conifer species is a primary factor to determine quality of paper and wood products. However, TL in Pinus densiflora Siebold & Zucc., a dominant conifer species in Korea, has not been monitored systematically across the country yet. To this end, the TL of early- and latewoods of Korean red pine from 16 provinces of the Republic of Korea was measured and compared to verify the differences (1) between the monitoring years (2014-2018), (2) between early- and latewoods of the trees from the same provinces, and (3) between the early- and latewoods from different provinces. Analysis of 31,500 tracheids revealed that the variation of TL of early- and latewood from two and six out of 16 sites, respectively, were not statistically meaningful and the TL of latewood displayed a lower annual variation than that of the earlywood during the monitoring years. The TL of the latewood was longer than that of the earlywood; however, four out of 16 sites showed shorter TL for the latewood. So, it was verified that the relationship between the TL of the early- and latewood can change. Moreover, the TL was longer for the trees located in the southeast regions.