Determination of Boundary between Core and Outer Wood by Radial Variation Modeling in Tropical Fast-Growing Tree Species

Boundary between core and outer wood should be clarified for tropical fast-growing tree species to utilize its wood resources under sustainable forestry. This study aimed to determine the boundary between core and outer wood based on the mixed-effects models for radial variations of anatomical characteristics and wood properties in three fast-growing tree species grown in community forests in Indonesia - Acacia mangium Willd., Maesopsis eminii Engl., and Melia azedarach L.. On the basis of the results of the radial variation modeling, almost all anatomical characteristics and wood properties were shown to increase or decrease from pith to bark and then become almost stable. The boundary values between core and outer wood based on exponential function with plateau for absolute changing ratios of estimated properties were 6.1, 6.8, and 5.5 cm for A. mangium, M. eminii, and M. azedarach, respectively. In conclusion, boundary between core and outer wood in respect to multiple characteristics and properties in tropical fast-growing tree species can be determined by combination of mixed-effects modeling and exponential function with convergence.