Increasing liana abundance and biomass in tropical forests: Emerging patterns and putative mechanisms

Background/Question/Methods

Tropical forests contain more than half of the earth’s terrestrial species and contribute more than a third of global terrestrial carbon stocks as well as nearly a third of terrestrial net primary productivity.  Thus, any alteration to tropical forests has important potential ramifications for species diversity, productivity, and the global carbon cycle.  Tropical forests are now experiencing large-scale structural changes, the most apparent of which may be the increase in liana (woody vine) abundance and biomass.  Lianas permeate most lowland tropical forests, where they can have a huge effect on tree diversity, recruitment, growth, and survival, which, in turn, can alter tree community composition, carbon storage, and carbon, nutrient, and water fluxes.  Consequently, increasing liana abundance and biomass have potentially profound ramifications for tropical forest composition and functioning.  To date, however, we lack a synthetic examination of the change in liana abundance and biomass in tropical forests.  Here, we synthesize the all of the available data to conclude that lianas are increasing in abundance and biomass in neotropical and subtropical forests.

Results/Conclusions

Currently, eight studies support the pattern of increasing liana abundance and biomass in neotropical and subtropical forests, whereas no studies from the neotropics reported a decrease or no change.   The putative mechanisms to explain increasing lianas include increasing evapotranspirative demand, increasing forest disturbance and turnover, changes in land use and fragmentation, and elevated atmospheric CO₂.  Each of these mechanisms probably contributes to the observed patterns of increasing liana abundance and biomass, and the mechanisms are likely to be interrelated and synergistic.  To determine whether liana increases are occurring throughout the tropics, and to determine the mechanisms responsible for the observed patterns, a widespread network of large-scale, long-term monitoring plots combined with observational and manipulative studies that more directly investigate the putative mechanisms are essential.