It’s not just Tarzan who liked lianas – Darwin did too

Plant ecologists have long sought to classify the bewildering variety of plant species into a manageable number of functional types that could be used to represent the essential characteristics of particular biomes or vegetation of geographic areas. Commonly recognized functional types include trees, shrubs, herbs, graminoids and climbers. Climbers, also known as vines, are plants rooted in the soil that are incapable of autonomuos vertical growth above a certain height and must rely on external support. Commonly, a distinction is made between herbaceous vines and lianas, the latter exhibiting a significant degree of woodiness. These plants have long attracted the interest of botanists because of their peculiar climbing mechanisms (Darwin, 1865).

Lianas constitute a major functional type in temperate, and especially in tropical zones. Liana research has recently been stimulated by their increasing presence and even dominance in disturbed vegetation and the discoveries of the multifaceted role they play in forest dynamics. A number of questions still need to be answered with respect to biological characterization of lianas as a group. This review in Annals of Botany addresses functional characteristics of wild lianas while focusing on whole-plant resource allocation, growth rate and some organ-specific structural and functional features of leaves, stems and roots.

Wyka, T.P., Oleksyn, J., Karolewski, P., & Schnitzer, S. A. (2013) Phenotypic correlates of the lianescent growth form: a review. Annals of botany, 112(9), 1667-1681.
Background: As proposed by Darwin, climbers have been assumed to allocate a smaller fraction of biomass to support organs in comparison with self-supporting plants. They have also been hypothesized to possess a set of traits associated with fast growth, resource uptake and high productivity.
Scope: In this review, these hypotheses are evaluated by assembling and synthesizing published and unpublished data sets from across the globe concerning resource allocation, growth rates and traits of leaves, stems and roots of climbers and self-supporting species.
Conclusions: The majority of studies offer little support for the smaller allocation of biomass to stems or greater relative growth rates in climbers; however, these results are based on small sized (<1 kg) plants. Simulations based on allometric biomass equations demonstrate, however, that larger lianas allocate a greater fraction of above-ground biomass to leaves (and therefore less biomass to stems) compared with similar sized trees. A survey of leaf traits of lianas revealed their lower average leaf mass per area (LMA), higher N and P concentration and a slightly higher mass-based photosynthetic rate, as well as a lower concentration of phenolic-based compounds than in woody self-supporting species, consistent with the specialization of lianas towards the fast metabolism/rapid turnover end of the global trait spectra. Liana stems have an efficient hydraulic design and unique mechanical features, while roots appear to penetrate deeper soil levels than in trees and are often able to generate hydraulic pressure. Much remains to be learned, however, about these and other functional specializations of their axial organs and the associated trade-offs. Developmental switches between self-supporting, searcher and climbing shoots within the same individual are a promising field of comparative studies on trait association in lianas. Finally, some of the vast trait variability within lianas may be reduced when species with different climbing mechanisms are considered separately, and when phylogenetic conservatism is accounted for.