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.