Evaluation of relationships between age-related changes in radial growth increments of stems and wood properties in Paulownia tomentosa trees grown in Fukushima, Japan: RADIAL GROWTH AND WOOD PROPERTIES IN PAULOWNIA TOMENTOSA

The information on the relationship between age-related changes in stem size and wood properties is essential for promoting plantation forestry and wood utilization using fast-growing tree species. In this study, age-related changes in radial growth increments of stems and wood properties were preliminarily examined using mixed-effects modeling in about 25-year-old Paulownia tomentosa trees planted in Fukushima, Japan. Gompertz model was well-fitted to age-related changes in stem diameter. The cambial ages showing the maximum current annual increment and mean annual increment estimated by the radial growth model were 5.4 and 7.3 yrs, respectively. Although radial growth decreased after certain cambial age, the mean annual increment value still showed more than 2 cm per yr until 25 yrs. Most anatomical characteristics increased from the pith and stabilized towards the cambium. On the other hand, physical and mechanical properties were stable from the pith towards the cambium: the fixed-effect parameter estimates in the selected y-intercept model were 0.29 g • cm–3 for air-dry density, 4.02 GPa for MOE, and 40.3 MPa for MOR, respectively. Thus, a large volume of xylem with low and stable values of physical and mechanical properties was produced for more than 20 yrs, suggesting that the rotation age of the plantation of this species can be determined from the viewpoints of wood quantity.In addition, the wood that forms at any cambial age can be used for utility applications.