Liana-tree competition and the ramifications for tropical forest diversity and carbon dynamics
Tropical forests store more than one-third of all terrestrial carbon and account for over one-third of terrestrial net primary productivity, and thus they are a critical component of the global carbon cycle. Nearly all of the aboveground carbon in tropical forests is held in tree biomass, and long-term carbon fluxes are balanced largely by tree growth and tree death. Therefore, the vast majority of research on tropical forest carbon dynamics has focused on the growth and mortality of canopy trees. Competition among trees is thought to be a zero-sum-game in terms of carbon dynamics; however, across growth forms the zero-sum-game assumption breaks down. For example, competition between lianas (woody vines) and trees may result in forest-wide carbon loss if lianas fail to accumulate the carbon that they displace in trees. Lianas may also stabilize or destabilize tree species diversity if lianas affect some tree species more than others. We tested these hypotheses using a series of large-scale liana-removal studies in gaps and in intact forest in the Republic of Panama.
We found that lianas competed intensely with trees, limiting rates of tree growth, sap-flow, seedling regeneration, and reproduction. Liana competition had a similarly negative effect on all tree species examined. Lianas significantly reduced carbon accumulation in trees, but lianas themselves could not compensate for the carbon that they displaced in trees. Therefore, lianas have a multi-pronged effect on many aspects of tropical forest diversity and dynamics, and the recently observed increases in liana density, biomass, and productivity in neotropical forests will likely result in lianas assuming a greater role in future tropical forest dynamics and the global carbon cycle.