Lianas reshape tree height allometry across tropical forests

Lianas exist in virtually every tropical forest, play a vital role for their functioning but also exert a strong pressure on their hosting trees. The exact influence of lianas on tree structure is poorly understood, despite its potential implications. Here, we investigated the relationship between liana infestation and tree height across the pantropics. Our analysis based on 50,473 tree records revealed substantial individual tree height reduction with liana infestation. Controlling for species, size and site, trees were on average 4.2% and 7.8% shorter when moderately and heavily infested by lianas compared to their liana-free counterparts. Substantial tree height reduction for heavily infested trees was found in a majority of the abundant species in our dataset, as well as in 46 of the 66 sites that we compiled in this study. Among the sites where a substantial liana-induced tree height reduction was identified, its magnitude varied between 3.6% and 39.3% for a 50 cm DBH tree under heavy liana infestation. Liana impact on tree height varied with disturbance, elevation and climate. In lowland, old-growth forests, liana impacts on tree height strengthened under drier conditions and warmer temperature regimes, particularly in sites characterised by higher minimum temperatures, warmer warm-season conditions, and reduced thermal seasonality. As global warming is predicted to exacerbate these climatic drivers, individual tree height reduction with heavy liana infestation could aggravate pantropically by 48% (middle of the road emission scenario) to 92% (business as usual) by the end of this century. Given the central role of tropical forest structure in governing carbon sequestration and climate feedback, these findings, coupled to the globally observed increase in tropical liana abundance, suggests that lianas could disproportionately influence Earth system functioning under future climate change.