Radial variation of wood anatomical characteristics and demarcation of juvenile and mature wood in two slash pine (Pinus elliottii) half-sib families

Summary Understanding the radial anatomical variation and determining the transition between juvenile and mature wood is crucial for enhancing harvesting efficiency and resource utilisation of Pinus elliottii . In this study, two slash pine half-sib families, A04 and A05 less investigated, were selected to study the radial variation of wood anatomical characteristics, i.e. annual ring width, latewood ratio, tracheid length, tracheid length-to-width ratio, double wall thickness, and wall-to-lumen ratio. Specifically, annual ring width decreased from pith to bark, whereas latewood ratio, tracheid length and tracheid length-to-width ratio both of earlywood and latewood, double wall thickness and wall-to-lumen ratio of latewood increased. Moreover, annual ring width, latewood ratio, tracheid length and tracheid length-to-width ratio both of earlywood and latewood, and wall-to-lumen ratio of earlywood were identified as suitable for distinguishing juvenile from mature wood. Additionally, the double wall thickness of latewood proved effective for demarcation in A05. Nevertheless, results revealed that double wall thickness of both earlywood and latewood, as well as wall-to-lumen ratio of latewood, were insensitive indicators for demarcation in A04. Similarly, the double wall thickness of earlywood and the wall-to-lumen ratio of latewood were not sensitive to the demarcation between juvenile and mature wood in A05. Furthermore, the transition from juvenile to mature wood of two half-sib families was evaluated using a segmented regression model and a cubic polynomial third-order regression model. Distinct maturation patterns illustrated A04 exhibited juvenile wood formation during the period of years from 2 to 10, followed by a transitional period from 10 to 15 years before reaching maturity from 15 to 18 years, while A05 demonstrated different development with the transition from 8 to 11 years. Furthermore, a third-order polynomial regression model was fitted for each anatomical trait within distinct growth stages. Systematic anatomical characteristics and determination of juvenile and mature wood constitute critical evidence for guiding family selection in silviculture and optimising processing parameters in wood industries.