and

This is the third and final paper in a three-part series investigating the effect of location within a tree on the mechanical properties of individual wood tracheids. This paper focuses on the definition of juvenile, transition, and mature zones as classified by fiber stiffness, strength, microfibril angle, and cross-sectional area. The average modulus of elasticity and ultimate tensile stress of all loblolly pine fibers were, in equal proportion of earlywood and latewood ' 17.3 Gpa and 824 Mpa, respectively. The average microfibril angle was found to be 15.4 degrees, with rings 5 and 48 averaging 26.8 and 6.1 degrees, respectively. Normalization of all mechanical and physical properties showed that the juvenile zone is not cylindrical but rather biconical, tapering from stump to below the live crown and then again from the live crown to the bole tip. The transition zone parallels the juvenile zone, ranging in width from 3 to 15 rings. Fiber properties continued to improve slightly throughout the duration of the mature zone