Rising CO2 Levels Improving Tree Growth

Published April 1, 2010

Rising amounts of atmospheric carbon dioxide are benefitting tree growth, with forests in the Chesapeake Bay region growing two to four times faster than expected, scientists report in Proceedings of the National Academy of Sciences.

Greatly Accelerated Tree Growth
Scientists at the Smithsonian Environment Research Center tracked tree growth in stands of Chesapeake Bay hardwoods over a 22-year period. Higher than expected circumference measurements showed the trees were growing much faster and producing much more biomass than expected as atmospheric CO2 levels rose

“Using a unique dataset of tree biomass collected over the past 22 years from 55 temperate forest plots with known land-use histories and stand ages ranging from 5 to 250 years, we found that recent biomass accumulation greatly exceeded the expected growth caused by natural recovery,” the study explained.

“We have also collected over 100 years of local weather measurements and 17 years of on-site atmospheric CO2 measurements that show consistent increases in line with globally observed climate-change patterns. Combined, these observations show that changes in temperature and CO2 that have been observed worldwide can fundamentally alter the rate of critical natural processes, which is predicted by biogeochemical models,” the study observed.

Other Factors Ruled Out
A Smithsonian press release accompanying the study emphasized the scientists wanted to know not just how quickly trees are growing but also what factors are causing the unexpectedly strong growth rates.

“It was not enough to document the faster growth rate; Parker and McMahon wanted to know why it might be happening. ‘We made a list of reasons these forests could be growing faster and then ruled half of them out,’ said Parker. The ones that remained included increased temperature, a longer growing season and increased levels of atmospheric CO2,” the Smithsonian press release explained.

CO2 Assists Plant Growth
Craig Loehle, an expert in tree growth at the National Council for Air and Stream Improvement, is not surprised by the tree growth findings in the Proceedings study and new data from the U.S. Forest Service.

“If it gets warmer and wetter, trees will be happy,” Loehle notes. “More carbon dioxide will also increase tree growth.”

Loehle notes most projections show there will be more trees and fewer droughts in North America in the next 100 years.

“The Forest Service’s models show a generally greener and more productive North America over the next 100 years, with a few drought spots,” he said.

Loehle noted satellite imagery shows world tree growth is increasing worldwide. Rising carbon dioxide levels will also help with global food production, Loehle observed.

“Globally, net primary productivity is up 6 percent over the past 25 years,” said Loehle. “This is noticeable in the Amazon, Boreal [an extensive forest area ringing the Northern Hemisphere], and in Northeastern America, all based on satellite data. The same applies to agriculture.”

Thomas Cheplick ([email protected]) writes from Cambridge, Massachusetts.