Changes in leaf morphology and anatomy with tree age and height in the broadleaved evergreen species, Eucalyptus regnans F. Muell

Relatively little is known about changes in leaf attributes over the lifespan of woody plants. Knowledge of such changes may be useful in interpreting physiological changes with age. This study investigated changes in leaf morphology and anatomy with tree age and height in the broadleaved evergreen species, Eucalyptus regnans. Fully expanded leaves were sampled from the upper canopy of tree ages ranging from 6 to 240 years, and tree heights ranging from about 10–80 m. There were significant changes in leaf form with increasing tree age and height. Leaf size and specific leaf area (SLA; leaf area/leaf mass) decreased, leaf thickness increased, and leaves became narrower relative to their length, with increasing tree age and height. Cuticle thickness and leaf waxiness, including wax occlusion of the stomatal antechamber, increased with increasing age and height. By comparison, there were no clear trends in stomatal frequency or stomatal length with tree age, although there were curvilinear relationships between an index of total stomatal pore area per leaf lamina and both tree age and tree height. The results support the hypothesis that leaves of E. regnans become more xeromorphic with tree age and height. The results are discussed in relation to their significance for changes in water relations in the canopy with age.