HEIGHT GROWTH STRATEGIES IN OPEN-GROWN TREES

This paper analyses the height growth of open-grown trees as a compromise between reducing self-shading by decreasing foliage density, and reducing structural costs by controlling crown dimensions. Self-shading is described with an equation which accounts for the reduction of foliage-specific photosynthesis due to increased volume density of foliage. Tree growth is described using a differential equation based on the carbon balance, where allocation of growth between wood and foliage follows the pipe-model theory. Crown shape is constant and crown length is equal to tree height. In this model, the construction and maintenance costs of wood relative to photosynthetic production increase with decreasing foliage density in the crown. The main result is that optimal height growth for maximizing accumulated net production is a bell-shaped function of time and rather independent of parameter values. As a result of optimal height growth, foliage biomass follows an allometric function of tree height. The allometric exponent is in the range 2-3, depending on the environmental parameters. The model is most sensitive to the fertility of the growth site, such that fertile sites favour low values and poor sites high values of the exponent. The results are compared with Scots pine and red pine trees grown in the open. The empirical material is consistent with the model. © 1992 Academic Press Limited.