Thursday, 26 May 2011

"All the Trees Will be Very Unhappy"

The ongoing effort to protect and revitalise forests is one of the key ways people are coming together to combat climate change.  Deforestation, after all, is responsible for around 20% of global greenhouse gas emissions.

Now, ecologists are hinting that climate change is causing yet another harmful feedback loop that reduces forests' ability to store carbon.

Throughout the tropics, lianas compete with trees for light, water and soil nutrients.  These fast-growing vines use the tree trunks for support and then sprout luxuriant leaves when they reach the tree canopy.  Where lianas are particularly aggressive, trees are weaker and die faster.  In some cases, they become so thick that trees are more easily blown over in heavy wind and rain.  The fallen trees die, but the flexible lianas survive and sprout new shoots.

As ecologist Dr. Stefan Schnitzer notes in the New York Times article, “If you come back in a year, it will have changed,” he said. “There will be a whole lot of vines in there, all rooted, all growing. And all the trees will be very unhappy.”

Faster growing trees are better able to compete with lianas, but these tend to have softer, less dense wood - which stores less carbon.  All told, the growth of lianas can reduce the carbon storage capacity of a forest by as much as 10%, according to the article.

Now for the climate feedback connection: lianas appear better able than trees to adapt to extended dry periods, precisely the conditions expected in much of the tropics as the planet warms. Lianas also appear more effective at utilising extra carbon dioxide to form new growth, so increasing atmospheric CO2 concentrations could be enhancing lianas' competitive advantage versus slower-growing trees.  In other words, human activity may be impeding forests' ability to absorb CO2, which makes it harder to reduce CO2 concentrations.

Long-term studies to understand how lianas and trees interact are just beginning, but this is a sobering reminder of the unanticipated effects of global climate change.