Climbing mechanisms as a central trait to understand the ecology of lianas -- a global synthesis.

Lianas are a distinctive component of tropical forests and their increase in abundance may have profound ramifications for forest composition and ecosystem functioning. However, so far, the current view considers lianas as a single, functional plant type and, therefore, ignores the life history differences among species resulting from their climbing mechanisms. Here, we integrate data from the main functional traits used to characterize plant form and function with global abundance data to reveal that lianas consistently have differences associated with their main climbing mechanisms. Overall, lianas with active climbing were characterized by an acquisitive strategy, showing higher specific leaf area, foliar nitrogen and slightly higher (marginally significant) maximum photosynthetic rates compared to lianas with passive climbing. Using structural equation modeling, we show that across the tropics the abundance of lianas with active climbing is mainly determined by forest structure (stem size distribution). Our study shows that active and passive climbing lianas clearly diverge in their functional traits and factors affecting their distribution. We conclude that a shift in the current view, where lianas are considered a single, functional plant type, is urgently needed to increase our predictability of their effects on tropical forests in the future.