The importance of including lianas in global vegetation models

Tropical forests are essential components of the earth system and play a critical role for land-surface feedbacks to climate change.These forests are currently experiencing large-scale structural changes, of which the most apparent may be the increase in liana abundance and biomass.The first study that documented liana proliferation in the Neotropics (1) was initially debated but later confirmed by multiple other studies (2).The consensus on liana proliferation led to speculations that this phenomenon could potentially have large impacts on the carbon cycle of tropical forests.But experimental proof for such speculations was lacking until recently.In their recent study, van der Heijden et al.(3) show for the first time that lianas substantially reduce tropical forest carbon storage.The study is based on a well-developed liana-removal field experiment.The experiment was performed over a limited period (3 y), in an area with particular high liana abundance in Panama, and therefore still needs to be confirmed by long-term studies elsewhere in the tropics.Nevertheless, the results are striking.By comparing natural forests with forests where lianas are artificially removed, the authors found that forests with lianas reached only 24% of their carbon sink potential compared with liana-free forests.Lianas were shown to reduce tree growth and recruitment, to increase tree mortality, and to shift carbon allocation to leaves rather than woody tissue.Based on this study (3), it is now clear that liana proliferation has a potential high impact on the future carbon cycle of tropical forests.We speculate that this impact might even be strengthened by the long-term impact lianas have on forest species composition and demography.