Evaluation of Relationships Between Cambial Age-Related Changes in Radial Growth Increments of Stems and Wood Properties in Paulownia tomentosa Trees Grown in Fukushima, Japan

Abstract

Information on the relationship between cambial age-related changes in stem size and wood
properties is essential for promoting plantation forestry and utilization of fast-growing tree species. In this
study, cambial age-related changes in radial growth increments of stems and wood properties were preliminarily
examined using mixed-effects modeling of 25-yr-old Paulownia tomentosa trees planted in
Fukushima, Japan. A Gompertz model was well-fitted to cambial 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 yr, respectively. Although radial growth decreased after a
certain cambial age, the mean annual increment value was still more than 2 cm per year until 25 yr. Most
anatomical characteristics increased from the pith and stabilized toward the cambium. On the other hand,
physical and mechanical properties were stable from the pith toward 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. Thus, a large volume of xylem with low and stable physical and mechanical properties
values was produced for more than 20 yr, suggesting that the rotation age of plantations of this species
can be determined from the viewpoint of wood quantity. In addition, the wood can be used where low
density, but stable properties is an advantage at any age in this species.