Like most other species, sustainable management of mahogany in natural forests ultimately relies on continued seed production by the population. Because larger trees produce more fruit, previous authors have emphasised the importance of retaining large trees. In this paper, we investigate levels of fruit production of mahogany in two ecologically distinct forests. Fecundity was related to tree size in some years, but this relationship was neither consistent nor strong. The contribution of any given size class to population-level fruit production depended on both its fecundity and its relative abundance and this differed between forests. The fecundity of small and medium-sized trees was also significantly different between forests and this was consistent with patterns of increased crown exposure caused by differences in forest structure. From a forest management perspective, these results suggest that size-fecundity relationships are insufficient to guide forest management prescriptions without also quantifying the size structure of the population.