Lianas are key contributors to the ecology of tropical forests, where they compete intensely with trees. Lianas suppress tree growth, survival and fecundity, which ultimately reduce tree biomass accumulation and decreases the capacity of tropical forests to store and sequester carbon. Previous experimental removal projects have quantified the total effect of lianas on tree growth; however, no study has experimentally manipulated multiple levels of liana infestation in trees, which limits the ability to predict how small changes in liana infestation will affect host trees. In this study, we tested the hypothesis that tree growth rate of (and thus carbon accumulation) would be proportional to the level of liana infestation. In 2012, we measured tree diameter and installed dendrometer bands in 140 mature canopy trees that were infested by lianas in a secondary forest in Panama. One year after (in 2013), we reduced liana infestation on each target tree by cutting either 10%, 25%, 50%, 75%, 90%, or 100% of liana basal area infesting the tree crown, which we compared to un-manipulated control trees (i.e. no liana stems cut).
Over two years, tree diameter growth was positively related to the percentage of lianas removed, with average growth in the 100% removal treatment being four-times greater than that of the control trees. Growth of trees in the low and intermediate liana removal levels were intermediate to the control and 100% removal treatments. This study demonstrates that even small levels of liana infestation (50% or less) substantially reduces tree growth, and that high levels of liana infestation (> 50%) have an even greater effect on tree growth.