Juvenile/Mature Wood Transition in Loblolly Pine as Defined by Annual Ring Specific Gravity, Proportion of Latewood, and Microfibril Angle

The length of juvenility or number of years a tree produces juvenile wood at a fixed height can be defined by the age of the wood at which properties change from juvenile to mature wood. This paper estimates the age of transition from juvenile to mature wood based on ring specific gravity (SG), proportion of annual ring in latewood, and ring average microfibril angle (MFA). The threshold method and the segmented modeling approach were used to estimate the age of transition. Twenty loblolly pine ( Pinus taeda L.) plantations, 20-27 years old, were sampled across five physiographic regions in the southern United States. Increment cores were collected at 1.3 meters from 15 trees in each stand to determine ring specific gravity and proportion of latewood by X-ray densitometry and annual ring MFA by X-ray diffraction. Precisely determining the transition age between juvenile and mature wood was difficult because transition is gradual, not abrupt. The age of transition was found to differ by wood property because these properties mature at different rates due to genetic and environmental factors. Both the threshold and the segmented model approach showed that transition age varied among regions. Both approaches showed that length of juvenility based on ring SG was shorter in the South Atlantic and North Atlantic Coastal Plains (ranging from 5.5 to 7.9 years) compared to that in the Hilly Coastal Plain that ranged from 10.4 to 13.6 years. Using MFA to estimate the age of demarcation, both approaches showed the South Atlantic, Gulf Coastal, and Hilly Coastal Plains had shorter lengths of juvenility (ranging from 8.4 to 10.4 years) than the Piedmont and North Atlantic Coastal Plain (ranging from 10.5 to over 20 years).