Bigger trees grow faster than smaller ones, contradicting previous assumptions that growth rates slowed with age, according to a study in the journal Nature. That means larger trees will absorb carbon dioxide faster.
Growth rates increased with size in 97 per cent of tropical and temperate trees, according to a study published today of more than 650,000 individual trees from 403 species. As part of photosynthesis, trees absorb greenhouse gases that cause global warming.
The results may change the way researchers create climate models, said Nate Stephenson, a forest ecologist with the U.S. Geological Survey in Three Rivers, California. Under the United Nations clean development mechanism, large-scale tree planting projects in developing countries may apply for emissions credits that can be traded and sold.
"This finding is going to be surprising to a lot of people," said Stephenson, who co-wrote the study. "Let's say you're the manager of a sports team -- what we found is the equivalent of your star players are a bunch of 90-year-olds. In human terms, we expect our star players to be in their 20s, 30s, maybe in their 40s, but not in their 90s."
Less mature forests still play an important role in sucking carbon from the atmosphere, he said, in part because there are more younger trees than older ones.
"In these old forests, which already hold a huge amount of carbon in them, it turns out that the star players are the biggest trees in old forests," Stephenson said yesterday in a telephone interview. "If you're trying to look at the role of forests in the future and feedbacks to climatic changes, you've got to get the players right."