Simulating Stationary Size Distribution of Trees in Rain Forests

A simple dynamic model of the distribution of tree size (trunkdiameter) in natural rain forests is presented. Based on dataof permanent plot measurements in a tropical rain forest anda warm-temperate rain forest, the cumulative basal area densityof trees larger than a given tree, at any particular time, isused to express the effect of suppression, or one-sided competition,on the growth rate of that tree. It also shows that increasingthe basal area density of all trees in the stand depresses therate of recruitment from the pool of seedlings. Mortality istreated as independent of the cumulative basal area. Simulationwith the model, applying the one-dimensional drift-diffusionequation, reproduces the observed course of reforestation afterclear-felling and leads to convergence to a unique stationarysize distribution by 200 years. This concuts with the size distributionobserved in primary forest stands. The present model representsan extension of density-dependent population growth models tosize-structured tree populations. Competition, cumulative basal area, density dependence, equilibrium, population, simulation, size distribution, tropical rain forest, warm—temperate rain forest