Lianas and vines are climbing plants that act as structural parasites of trees, generally reducing host tree survival, growth, and reproduction. Previous studies suggest co-occurring tree species often differ in levels and impacts of infestation with lianas and vines, yet the role of these biotic interactions in structuring tree communities has remained largely unexplored. We describe multiple pathways by which climber-tree interactions could alter relative competitive ability of tree species and/or modify niche structure of tree communities. We quantitatively evaluate several such effects for lianas infesting trees in the tropical forest on Barro Colorado Island (BCI), Panama. We utilize observations of liana load (proportion of the crown covered by lianas) for 6832 trees of 33 tree species, together with previously established species-specific relationships of liana load with tree growth, survival, and reproduction, integrated with whole life cycle data in integral projection models to estimate per capita population growth rates. We investigate how tree species relationships with lianas vary in relation to tree species shade-tolerance and leaf size, and in relation to liana species climbing mode. We define a tree species’s liana burden as the decrease in estimated population growth rate from liana-free conditions to its current levels of liana infestation.
Results/Conclusions
The most obvious potential impact of lianas is as relatively generalized natural enemies to which tree species are differentially resistant or tolerant, thereby altering tree species competitive rankings. Our 33 focal tree species varied widely in liana burden, and these differential burdens results in large shifts in rankings of per capita population growth rates between current liana infestation levels and liana-free conditions. Shade-tolerant species had lower liana burdens than light-demanding species, suggesting that lianas alter niche structure with respect to shade-tolerance, increasing the relative abundance of shade-tolerant species. Insofar as generalized liana pressure is spatially and/or temporally variable, lianas may also alter spatial and temporal storage effects that contribute to niche differences among tree species. In addition, lianas may generate new axis of niche differentiation among tree species if different tree trait combinations confer resistance or tolerance to different groups of lianas, leading lianas to act as (semi-)specialized natural enemies. Tree species shade-tolerance and leaf size are differentially associated with the prevalence of lianas having different climbing modes in our study system, consistent with semi-specialization. We conclude that lianas can and probably do play important roles in structuring many tree communities, and that these effects deserve further study.