Marquette researchers determine woody vines in Panama diminish tree reproduction

June 12, 2017

MILWAUKEE — Competition from woody vines, called lianas, significantly reduces tree reproduction in tropical forests, Marquette University researchers found in a new study.

The findings, published in the Journal of Ecology, were the first experimental demonstration that competition from lianas dramatically reduces the ability of community-level canopy trees to reproduce.

These vines climb trees to reach the forest canopy, where their leaves absorb the sunlight required for tree growth. Lianas ultimately could have a destabilizing effect on trees and animals in tropical forests, the researchers said.

"Many of the animals in the forest depend on fruit from trees to survive," said Maria Garcia-Leon, the lead author on the study. "Since the number of lianas are increasing while reducing the ability of trees to reproduce, it could reduce the amount of food available to these animals."

Unlike trees, most lianas do not produce the kinds of fruits that are favored by animals, meaning that if lianas displace trees they could also displace many animal species.

The research was conducted from the lab of Stefan Schnitzer, a Marquette professor of biological sciences. Schnitzer, who also is a research associate at the Smithsonian Tropical Research Institute, has led many studies on the effects of lianas, which are increasing in abundance, in tropical forests.

"This is the first experimental demonstration that lianas reduce reproduction across the entire canopy tree community" Schnitzer said. "By reducing the ability of canopy trees to reproduce, far fewer seeds are dispersed into the surrounding forest, which can influence tree diversity and the composition of the tree community."

The researchers studied 576 canopy trees (comprising 65 tree species), 85 palms and 617 understory plants on Gigante Peninsula, which is part of the Barro Colorado National Monument in central Panama. In 2011, the tropical ecologists removed all lianas from 12.6 acres of forest while leaving lianas intact on adjacent plots of the same size.

Five years later, the plots with lianas removed had 150 percent more canopy trees with fruits than the other plot that still had the woody vines. Fruiting trees had 30 percent more of their canopy covered by fruits in plots where the lianas were removed than did trees in the control plots.

A lower number of flowers and fruits limits seed production and seed dispersal. Previous studies have shown that more seeds results in a larger number of plants and more species diversity.

Removing the lianas had "only a slight positive effect" on palms and understory tree flower and fruit production, the researchers said, demonstrating that lianas have the strongest competitive effect on canopy trees compared to the rest of the plant community.

Other researchers involved in the research included Laura Martinez-Izquierdo, an associate in the Schnitzer lab at Marquette; Felipe Nery Arantes Mello, a Marquette graduate student in biological sciences; and Jennifer S. Powers, associate professor of ecology at the University of Minnesota.