Increased Carbon Dioxide In Atmosphere Makes Trees More Efficient At Using Water

Trees located in forests around the world have been using water more efficiently over the past 20 years as carbon dioxide levels have increased in the Earth’s atmosphere, a new study published in Nature revealed.

The study, titled “Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise,” was based on data collected from forests in the northeastern United States and around the world.

“This could be considered a beneficial effect of increased atmospheric carbon dioxide,” Trevor Keenan of Harvard University and the lead author of the study, told the Harvard Gazette, on Wednesday.

“A large proportion of the ecosystems in the world are limited by water. They don’t have enough water during the year to reach their maximum growth. If they become more efficient at using water, they should be able to take more carbon out of the atmosphere due to higher growth rates.”

Terrestrial plants remove carbon dioxide from the atmosphere through a process called photosynthesis, which results in the loss of water vapor from leaves, a key characteristic of our ecosystem that is central to the global cycles of water, energy and carbon.

After analyzing long-term measurements of carbon and water exchange in the ecosystem, researchers found that there has been a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades.

“Our analysis suggests that rising atmospheric carbon dioxide is having a direct and unexpectedly strong influence on ecosystem processes and biosphere-atmosphere interactions in temperate and boreal forests,” Dave Hollinger, a plant physiologist with the U.S. Forest Service’s Northern Research Station, and a co-author of the study, said in a press release on Wednesday.

Efficient use of water by trees could enhance timber yields and improve water availability, which could partially offset the effects of future droughts. But, according to scientists, this very capability now seen in the world's trees could also reduce evaporation and plant transpiration to the atmosphere, which may lead to higher air temperatures, decreased humidity and reduction in the recycling of continental rainfall.

The study, published in Nature on July 10, was conducted in collaboration with researchers from Harvard’s Department of Earth and Planetary Sciences, the U.S. Forest Service, Ohio State University, Indiana University and the Karlsruhe Institute of Technology in Germany.

“This larger dataset will help us to better understand the extent of the response we observed,” Keenan said. “That in turn will help us to build better models, and improve predictions of the future of the Earth’s climate.”