Modelling Growth and Optimal Rotations of Tropical Multipurpose Trees Using Unit Leaf Rate and Leaf Area Index

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Abstract
A simple model of tree growth in even-aged stands calculated growth rate as the product of unit leaf rate (E) and leaf area per tree. Theoretical analysis showed that decreasing E with increasing leaf area index (LAI) depends on both allometry and current growth rate, which depend on planting density, growth history, and competition. A case study using Eucalyptus saligna grown in Hawaii found that the growth trajectories of four different planting densities can be representing by a single curve of E versus LAI. Using maximum mean annual increment (MAI) as the criterion for optimal rotation length, the model predicts increasing peak MAI from 16.4 to 21.5 ha-1 year-1 for initial planting densities, varying from 500 to 2000 trees ha-1. Over this range of initial densities, rotation age decreases from 9.0 to 4.7 years; at rotation age for these initial densities, trunk diameter decreases from 28 to 14 cm, total biomass decreases from 148 to 102 t ha-1, and LAI decreases from 4.0 to 2.9. Such synthesis and generalization from empirical growth trials will permit improved decision-making in the context of desired rotation characteristics. Extrapolation to other sites and species will require understanding of how key parameters vary, in particular those of the allometric equations and those describing the E-LAI relationship.