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News Article

Lianas suppress tree fruit in tropical forests

The vines compete with trees for light, water and nutrients

Woody vines, also known as lianas, compete intensely with trees, reducing tree growth, survival and recruitment and are on the increase in tropical forests.  A new study from the Smithsonian Tropical Research Institute, shows that lianas prevent canopy trees from producing fruit, with potential consequences for other forest inhabitants.

Lianas climb up the trunk of a tree to access the sunlit forest canopy where they spread their leaves, reducing the availability of light to their host trees.  Unlike the trees, lianas do not need to spend as much energy in making large stems to support themselves, as they use the architecture of the trees that support them.  They also compete for water, nutrients and other resources below the ground.

“Lianas are well known as rivals of trees in tropical forests because lianas compete with trees for sunlight; until this study, however, we didn’t know to what extent lianas actually reduce tropical tree reproduction,” says co-author Stefan Schnitzer.

Schnitzer and his team established 16 experimental plots where all trees and lianas greater than one centimetre in diameter were identified to species, tagged, mapped and measured.  In 2011, in eight of the plots the lianas were cut, leaving the remaining eight in the other plots for comparison.

In 2012, the plants growing on the ground under the trees were surveyed to see how many were producing fruit and flowers.  This was carried out again, for the trees in the canopy in 2013. A second census of all plants was undertaken in 2016, five years after the lianas were initially removed.

According to the research findings, the effects of removing the lianas were dramatic.  They noticed that only two years after the lianas were removed, the number of canopy trees bearing fruit was 173 percent higher in the plots where the lianas were removed than the plots that still had lianas.  Also, the number of tree species with fruits was 169 percent higher and fruiting trees had 50 percent more of their canopies covered with fruits. Five years after the lianas had been removed, the number of canopy trees with fruits was 109 percent higher and the fruiting trees had 31 percent more of their canopy covered by fruits.  In contrast, liana removal only slightly increased reproduction in understory plants and palms.

Previous research has shown that lianas affect reproduction in single species of trees.  However, this is the first experimental study to demonstrate the effects of lianas on the reproduction of an entire tree community.  As lianas flourish in tropical forests, their suppression of tree reproduction could change the dynamics of forest regeneration, threatening the high biodiversity of these forests.

“We suspected that lianas might have a negative effect on tree reproduction, but the strength of the effect, only five years after cutting the lianas, was surprising,” said lead-author Maria Garcia León.  “The seeds of most lianas in the tropical forests of the Americas are spread by the wind, whereas most trees seeds and fruit are spread by animals.  Therefore lianas reduce tree fruit production, but they don’t make up for it by producing their own fruit, which, potentially may deprive animals of food.”

Further information on lianas is available to subscribers of the Forest Science database.  For example, using the search terms "climbing plants" AND "tropical forests" yields 484 results.

Journal reference

María M. García León, Laura Martínez Izquierdo, Felipe Nery Arantes Mello, Jennifer S. Powers, Stefan A. Schnitzer. Lianas reduce community-level canopy tree reproduction in a Panamanian forestJournal of Ecology, 2017; DOI: 10.1111/1365-2745.12807

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 21 June 2017
  • Source
  • Smithsonian Tropical Research Institute
  • Subject(s)
  • Environment
  • Forest trees