Modelling growth and optimal rotations of tropical multipurpose trees using unit leaf rate and leaf area index.
Abstract
Theoretical analysis of a simple model, in which tree growth in even-aged stands is calculated as the product of unit leaf rate (E, increase in plant weight per unit of leaf area per unit of time) and leaf area per tree, showed that decreasing E with increasing leaf area index (LAI) depends on both allometry and current growth rate (related to planting density, growth history and competition). A case study for Eucalyptus saligna in Hawaii showed that growth trajectories for 4 different planting densities can be represented by a single curve of E versus LAI. Using maximum mean annual increment (MAI) as the criterion for optimal rotation, the model predicted increasing peak MAI from 16.4 to 21.5 t/ha for initial planting densities from 500 to 2000 trees/ha, with rotation age decreasing from 9.0 to 4.7 yr. At rotation age for these initial densities, stem diameter decreased from 28 to 14 cm, total biomass from 148 to 102 t/ha and LAI from 4.0 to 2.9. The importance is emphasized of including foliage as a yield component (e.g. as fodder) in a model for multipurpose trees.