A model of ecological processes that determine the behaviour of individual trees, and thus the overall characteristics of forest stands, is described, evaluated and discussed. The purpose of the model is to simulate individual trees as part of the SYMFOR framework for modelling the effects of silviculture on the growth and yield of tropical forests. The model encompasses the response of individual trees to a range of conditions, described in a spatially explicit form, that represent typical situations occurring in forests at all stages following management interventions. The model describes the processes governing the behaviour of trees, allowing it to be used with validity for simulations of management regimes that do not have experimental precedent. The model can thus guide or negate the requirement for lengthy and laborious field trials. Sub-models of tree growth, natural mortality and recruitment processes specify the ecological model. The growth model describes the annual diameter increment for an individual tree, calculated from a deterministic component using tree diameter, local competition (5 m radius), wider competition (30 m radius) and the effect of previous harvesting and a stochastic component representing the remaining variation. The mortality model represents the death of trees as a probability function that increases with diameter. Damage from falling trees is represented by a trapezium-shaped area in which all trees smaller than the falling tree are killed. The recruitment model uses 10 by 10 m grid-squares to represent the probability of recruitment of trees past the 10 cm diameter threshold of the SYMFOR framework based upon the average competition within a grid-square. The whole model is derived from data and does not rely on theories of tree or forest behaviour, but all aspects represent real forest processes. © 2002 Elsevier Science B.V. All rights reserved.