Lianas explore the forest canopy more effectively than trees under drier conditions

Lianas rely on trees for support and access to high-light positions in the forest canopy, but the implications for how lianas explore the canopy compared to trees remain understudied. We present an in situ forest canopy study to test the hypotheses that: (1) lianas favour leaf display over stem investment compared to trees and (2) lianas have greater potential to colonize non-shaded, high-light areas effectively than trees. We compared branches of 16 liana species with those of 16 sympatric tree species in the canopy of two lowland tropical forests with contrasting rainfall regimes in Panama using 40–50 m tall canopy cranes. One forest was relatively dry and seasonal in rainfall and associated solar radiation. The other forest was relatively wet and had a weaker seasonality. We observed that lianas were more efficient in leaf display over stem investment than trees, particularly in the forest with lower precipitation and stronger seasonality. Specifically, lianas had a lower LMA (leaf mass per unit leaf area), stronger apical dominance, higher stem slenderness and fewer leaf layers than trees. In the forest with higher precipitation and weaker seasonality, lianas also had stronger apical control and fewer leaf layers than trees, but both lianas and trees were relatively similar in LMA and stem slenderness. Our study shows that lianas more effectively explore the canopy than trees under drier conditions, but much less so under wetter conditions. We argue that lianas display a functional strategy that allows them to better intercept light than the tree species in forests with low precipitation and strong seasonality, while they are constrained to display such strategy at high precipitation – light-limited – sites. A free Plain Language Summary can be found within the Supporting Information of this article.