Age-related decline in forest growth: an emergent property

Proposed explanations for the age-related decline in forest production (i.e . 'culmination of current annual increment') generally fall into one of two categories: (1) the ecophysiology of individual, generally old, trees; and (2) structural changes at the population level associated with increasing stand age. The decline in production occurs in young forests, is substantia l at young stand ages, and timing of decline can be altered simply by chang es in stand density. Changes in physiology of old trees do not account for the near-universal decline in production in developing stands. Rather, peak production and its subsequent decline are associated with inevitable chang es in the structure of developing forest stands. Peak production almost inv ariably occurs as peak community leaf area is obtained. Substantial changes in canopy architecture, production efficiency, and tree population structu re occur at this point, resulting in declining stand-level production. Thes e changes are emergent properties that must be studied and understood at th e population level, and are not derived from individual tree physiological processes. (C) 2001 Elsevier Science B.V. All rights reserved.