How Do Changes in Leaf/Shoot Morphology and Crown Architecture Affect Growth and Physiological Function of Tall Trees?

Abstract

With increasing height within the crowns of tall trees, leaves tend to become smaller and thicker and shoots shorter. In tall trees, the vertical variation in leaf/shoot morphology is largely driven by water status. Morphological changes associated with increasing height in the crown present static constraints on photosynthesis, such as decreasing light intercepting area relative to leaf mass and decreasing CO2 diffusion rate inside the leaf. Despite high light availability, leaf-area-based photosynthetic rates at the tops of tall trees tend to be low and this may limit height growth. However, the observed changes in leaf/shoot morphology as well as xylem/leaf anatomy, and crown architecture may compensate for various physiological constraints associated with increasing tree height. Continuous renewal of branches and foliage through epicormic shoot production and the change from hierarchic to polyarchic crown architecture may allow large trees to maintain physiological function and continue to grow.