The proportion of carbon allocated to wood production is an important determinant of the carbon sink strength of global forest ecosystems. Understanding the mechanisms controlling wood production and its responses to environmental drivers is essential for parameterization of global vegetation models and to accurately predict future responses of tropical forests in terms of carbon sequestration.Here, we synthesize data from 105 pantropical old-growth rainforests to investigate environmental controls on the partitioning of net primary production to wood production (%WP) using structural equation modeling.Our results reveal that %WP is governed by two independent pathways of direct and indirect environmental controls. While temperature and soil phosphorus availability indirectly affected %WP via increasing productivity, precipitation and dry season length both directly increased %WP via tradeoffs along the plant economics spectrum.We provide new insights into the mechanisms driving %WP, allowing us to conclude that projected climate change could enhance %WP in less productive tropical forests, thus increasing carbon sequestration in montane forests, but adversely affecting lowland forests.