Urban warming slows tree growth, photosynthesis

https://www.eurekalert.org/pub_releases/2016-10/ncsu-uws100516.php

Public Release: 5-Oct-2016
Urban warming slows tree growth, photosynthesis
North Carolina State University

New research from North Carolina State University finds that urban warming reduces growth and photosynthesis in city trees. The researchers found that insect pests are part of the problem, but that heat itself plays a more significant role.

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The researchers found that scale insects and spider mites - well known tree pests - were more abundant at hotter sites. Specifically, they found that spider mite populations more than doubled when a site's average temperature crossed a threshold of 16.4 degrees Celsius (61.5 degrees Fahrenheit). Scale insects, however, showed a linear relationship with temperature. In other words, the hotter it got, the more scale insects there were.

The researchers also found that warming negatively affected tree photosynthesis and growth, regardless of whether pests were present.

"Trees that didn't have pests had more branch growth than trees with pests," Meineke says. "But trees at warmer sites had less trunk growth, which accounts for more tree biomass, regardless of pests."

The researchers then plugged these results into a model to determine the extent to which urban warming impacted carbon storage for all of the willow oaks in Raleigh.

"We found that urban warming reduced carbon storage by all of Raleigh's willow oaks by 12 percent, or 27 metric tons per year," Meineke says.

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