In lowland mixed-dipterocarp forests in Southeast Asia, synchronous mast reproduction involving various species and families occurs at irregular intervals of 2-10 y at community level. Most emergent trees, typically of the family Dipterocarpaceae, are involved in these events, but they seldom reproduce in other years. How do dipterocarp species respond to such a huge resources demand for mast reproduction in the tropical forest environment with low availability of soil nutrients, especially phosphorus? We investigated resources dynamics for reproduction and continuously monitored resources concentrations in an emergent dipterocarp species, Dryobalanops aromaticain , in Sarawak, Malaysia. As a result, the decrease in phosphorus concentrations in the trees during the reproductive period correlated significantly with their fruit produce in the reproductive years. In addition, reproductive individuals of this species had significantly higher phosphorus content in their stems than non-reproductive individuals just before flowering. Therefore, the accumulation of phosphorus may be the decisive factor in the occurrence and frequency of mast reproduction under relatively poor soil conditions prevalent in tropical rain forests in Southeast Asia.