| Summary: | The mechanisms through which tropical trees, and thereby tropical forest areas, regenerate themselves remain little understood. The area of greatest ignorance in the life cycle of tree species is the early pre-seedling stage and, therefore, a set of experiments to investigate this stage was undertaken. Firstly, a field experiment to measure the secondary dispersal dynamics of three pioneer tree species in the Barro Colorado Island (BCI) forest of Panamá was carried out. Seeds were sown out in the forest and later recovered by excavating the surface soil where they were sown. The results of this project gave an estimate of the displacement and burial percentages to be expected for a small clump of seeds dispersed onto the forest floor. An assessment was made of the relative importance of abiotic and biotic mechanisms of secondary dispersal. Secondly, a modelling and field experiment used a soil water and heat transport model to characterise and predict soil drying in forest gaps. A three scenario modification to the gap-understorey dichotomy was suggested by the field measurements and model results. Thirdly, a modelling project used s simulation of the ground-level radiation regime of a forest, based on data from BCI, to investigate the relationship between high light areas and the areas delimited as gaps according to four different definitions. In addition to proposing a new method of surveying large forest areas for gaps, this project produced a well-validated model of forest structure. Finally, the results and programme produced during these three projects were synthesised into a description of several forest simulation sub-models, and possible directions for further research were outlined that may combine these into a full simulation model for a tropical forest.
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