The Control of Tree Structure and Productivity Through the Interaction of Morphological Development and Physiological Processes

Abstract

The key to understanding how tree productivity is controlled, and how it may change in response to changes in environment, lies in understanding how morphology and physiology interact. Plant morphology determines both patterns of resource acquisition and the condition of the internal environment of the tree. Empirical evidence in support of these claims is presented and a theory is specified for the morphological control of physiological processes in crown and canopy growth. Three important postulates of this theory are that (1) multiple structural characters influence resource acquisition, (2) characters are not constant during tree growth but change over time, and (3) both the external and internal environment of the tree change over time. Two models are presented that are based on the principle that morphology determines patterns of resource acquisition and subsequent growth. One model, WHORL, simulates competition and, particularly, the effects of tree plasticity on the competition outcome. The other model, BRANCH, illustrates how different degrees of modular autonomy, when given to the component shoots of a branch, may markedly alter the patterns of foliage weight supported and estimates of export of photosynthate from the branch to the rest of the tree.