Vines use climate change to catch a ride on the trees

Tropical forests could initially benefit from climate change and the rise in carbon dioxide levels. And vines, in particular, are positioned to be the big winners.

Tropical forests are a rich and vibrant habitat — home to more than half of the planet’s species of plants and animals.

Yet though life flourishes in the hot, humid equatorial regions, competition for space is fierce. And as levels of carbon dioxide increase, the dynamics of species competition can be upset.

CO2 acts like a fertilizer for most plants, but new research shows the woody vines, or lianas, that thrive in the tropics are particularly well-suited to a more carbon-rich environment. And that's not necessarily good news for slower growing tropical trees.

Oliver Phillips, professor of geography at the University of Leeds in the UK, said the vines compete with trees by riding the trees to the top of the canopy. From there, they compete for sunlight and water.

"If you are a species of tree which has an architecture which is really vulnerable to liana infestation, you’re likely to get those extra lianas in you," he said. "If you happen to be, say a palm, which doesn’t have branches and it just goes straight up, and manages to shed, clean its trunk efficiently by dropping down leaves, in a liana rich world, you could actually have an extra advantage."

That means, in a CO2 rich world, the composition of our tropical forests is likely to change.

To be sure, the increase in CO2 is also good for the trees, which also metabolize and feed on the gas. In fact, virtually every plant should benefit from the higher levels of CO2. But lianas have an extra advantage, in that they let trees do most of the work to grow up into the canopy and the sun, Phillips said.

Eventually, however, that CO2 will change the climate more than it helps the trees. 

"In the Amazon the last few years, there’s been a series of intense droughts. Those droughts have tended to kill more trees than were dying before," Phillips said.

Phillips says he's already seeing signs that the increased mortality is countering any benefits from the increased levels of CO2.

"If that were to be the case, then instead of seeing a carbon sink, which is what we’ve been measuring in the Amazon for decades now, in the future we could actually see the system becoming a carbon source," he said.

And that would be a very bad situation. And, as for the lianas, if they weren't there, the trees would be doing a 20 percent better job of sequestering carbon and perhaps better staving off, or at least reducing, climate change.