Tropical forests are occasionally hit by intense disturbances like hurricanes or droughts that kill many trees. We found evidence for such intense disturbances in a tree-ring study on tropical forests in Bolivia, Cameroon and Thailand. To reconstruct past disturbances we applied ‘forensic forest ecology’, a combined analysis of age distributions and spatial distributions of trees. The study shows that all three forests carry a legacy of past disturbances. The process of recovery after past disturbance may explain recently reported increases in tree growth and forest biomass from long-term forest monitoring plots. This finding is in contradiction with the dominant paradigm that increases in forest biomass are the result of enhanced photosynthesis due to rising CO2 concentrations in the atmosphere. A more dominant role for past disturbances means that the compensating effect of tropical forests in global warming may be smaller than previously thought.