Scientists have discovered that climbing vines are upsetting the carbon balance of tropical forests by crowding out and killing trees. Rainforests play a vital role in the global carbon cycle. We depend on the trees found in these tropical areas to take up some of the carbon dioxide that we are emitting, so not all of our emissions end up in the atmosphere.

In a new study published in Proceedings of the National Academy of Sciences, and led by Dr Geertje van der Heijden from The University of Nottingham, researchers have found evidence that woody climbing plants - called lianas - are dramatically reducing the carbon uptake and storage of tropical forests by crowding out and killing trees.

Tropical forests store nearly 30 per cent of global carbon and contribute to 40 per cent of the global carbon sink. Lianas have drastically increased in both numbers and bulk in recent decades, and are restricting tree growth and even killing trees by their tangling presence.

During a three-year experiment, scientists were able to prove that lianas substantially reduce forest-level carbon uptake and storage.

Working in the Barro Colorado Nature Monument in Panama, Dr van der Heijden and her team, consisting of Dr Stefan Schnitzer (Marquette University, US) and Dr Jennifer S Powers (University of Minnesota, US), removed lianas from eight of 16 large (80-meter-square) plots of tropical forest, then tracked how much above-ground biomass - wood and leaves - accumulated in each plot over a period of three years.

Reducing tree growth and increasing tree mortality
The researchers found that the study plots with lianas collected 76 per cent less carbon in woody biomass over the experimental period because of reduced tree growth and increased tree death.

The team calculated that lianas could potentially reduce long-term storage of carbon in tropical forests by one-third or more.

Dr van de Heijden, from the School of Geography at The University of Nottingham, said: "Essentially lianas are reducing the amount of carbon being taken in by the forest and increasing the amount that's going out.

"To our knowledge, this is the first time that these liana effects have been experimentally tested on a whole forest level. It proves the important role of lianas in tropical forests, particularly in relation to carbon.

"Lianas are increasing in numbers and size (at least) in the tropical forests in Central and South American and so our findings have a great relevance when looking at the future fate of the tropical carbon balance, as well as for global levels of atmospheric carbon dioxide.

"Now we have evidence to prove the important role of lianas in the carbon balance of these forests, I would hope that this will be taken into account in climate and vegetation models to improve future predictions."