Older Trees Grow Faster, Take Up More Carbon

Trees' growth accelerates with age, according to a new study in the journal Nature, which suggests that the world's oldest trees could play an important role in combating climate change.

The revelation goes against the long-held assumption that trees lose their vigor with age. An analysis of more than 600,000 trees belonging to 403 species found that trees grow more as they get older, which enables them to trap more carbon than their younger counterparts.

"Rather than slowing down or ceasing growth and carbon uptake, as we previously assumed, most of the oldest trees in forests around the world actually grow faster, taking up more carbon," said Richard Condit, staff scientist at the Smithsonian Tropical Research Institute. "A large tree may put on weight equivalent to an entire small tree in a year."

The phenomenon would be akin to a human's growth continuing past adolescence instead of slowing down, the study' first author Nathan Stephenson, an ecologist with the US Geological Survey, said in a statement.

"By that measure, humans could weigh half a ton by middle age and well over a ton at retirement," Stephenson told the AFP.

Stephenson told the Nature blog that the trees "have the equivalent of an adolescent growth spurt, but it just keeps going."

One study site, an old-growth forest in the western US, the researchers found that trees with a diameter larger than 100 centimeters comprised just 6 percent of trees but accounted for one third of the growth in the forest.

One of the next steps in this research is to determine whether the accelerated growth of an individual tree will translate into greater carbon storage by aging forests. The answer will have an impact on a number of carbon sequestration programs that rely on the carbon-absorbing abilities of forests.

"We already knew that old forests store more carbon than young forests. But old forests contain trees of all sizes and it was not clearly understood which trees grew the fastest, removing the most carbon dioxide from the atmosphere," said Stephenson told the AFP.

But now the answer in clear.

"For reducing carbon dioxide in the atmosphere, more big trees are better!" he said.