A sonic aenomometer and air inlet tube on an eddy-covariance tower at University of Michigan Biological Station, Michigan, USA. The instruments allow for the continuous monitoring of gas exchange between the forest and the atmosphere. Credit: Chris Vogel

A study by scientists with the U.S. Forest Service, Harvard University and partners suggests that trees are responding to higher atmospheric carbon dioxide levels by becoming more efficient at using water.

The study, "Increase in forest water-use efficiency as  concentrations rise," was published on-line today in the journal Nature. Dave Hollinger, a  with the U.S. Forest Service's Northern Research Station, is a co-author with lead author Trevor Keenan of Harvard University and colleagues from The Ohio State University, Indiana University, and the Institute of Meteorology and Climate in Germany.

"Working with others, the Forest Service is developing knowledge that is essential to maintaining healthy, sustainable forests in a ," said Michael T. Rains, Director of the Northern Research Station. "We are striving to be at the forefront of delivering sound  to the public."

Terrestrial plants remove carbon dioxide from the atmosphere through photosynthesis, a process that is accompanied by the loss of water vapor from leaves. The ratio of water loss to carbon gain, or water-use efficiency, is a key characteristic of ecosystem function that is central to the global cycles of water, energy and carbon.

Scientists analyzed direct, long-term measurements of whole-ecosystem carbon and water exchange and found a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades.

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