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Net carbon uptake has increased through warming-induced changes in forest phenology

Net carbon uptake has increased through warming-induced changes in forest phenology

Research funded by the Climate Program Office has been accepted for publication into Nature Climate Change. The paper “Net Carbon Uptake has Increased Through Warming-Induced Changes in Forest Phenology,” was published June 1.
The researchers used remote sensing, ground observations of phenology, and flux tower measurements of forest-atmosphere exchange to examine the impact of shifts in forest phenology on ecosystem carbon cycling.
Scientists have known for many years that rising temperatures are lengthening the growing season in many northern and mid-latitude forests. New research indicates that in the eastern United States, increased carbon uptake has outpaced a simultaneous increase in carbon dioxide “exhaled” into the atmosphere through respiration. Overall, it seems that eastern forests are acting as increasing “sinks” for carbon dioxide.

One reason for the increased carbon uptake is that trees up and down the eastern half of the country are leafing out earlier in the spring. The map shows a trend toward earlier spring green-up over twelve years (2001-2012), based on both satellite vegetation data and ground observations from long-term research sites in forests across the Northeast. Shades of green indicate locations where the onset of spring is occurring earlier. White indicates very little change, while pink shows locations where the onset of spring is occurring later in the year. On average, spring is arriving about 10 days earlier than it used to only two decades ago.

The shift toward earlier spring leaf out is due to warming in the U.S. East, and has been mirrored by a delay in when trees drop their leaves in autumn. In a recent study published in Nature Climate Change, researchers found that enhanced “greening activity” during this extended growing season increased the amount of carbon that forests removed from the atmosphere through photosynthesis—the process by which plants convert carbon dioxide in the air into sugar molecules to use for food and to grow.

But just like animals do, plants and soil organisms burn sugars for energy and “exhale” carbon dioxide as a byproduct, a process known as respiration; warming also increases ecosystem respiration. While respiration increased in eastern forests during the extended growing season, the forests absorbed more carbon dioxide than they released, leading to a total net increase in carbon storage.
Visuals for this piece were created by the team and appeared on the inside cover of Nature Climate Change.
To view the full study, visit:

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