Urban Warming Slows Tree Growth, Photosynthesis

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."Earlier studies have shown that urban warming increases in pest abundance of street trees," says Emily Meineke, lead author of a paper describing the work. "We wanted to know how the urban warming and pest abundance Affect tree growth, since trees pull carbon out of the atmosphere and convert it into biomass. This is important, Because We know that high levels of atmospheric carbon play a role in climate change. "Meineke did the work while a Ph.D. student at NC State. She is now a postdoctoral researcher at Harvard.To explore this issue, Researchers went to 20 pairs of willow oak trees (Quercus Phellos) across Raleigh, North Carolina. At each site, one tree was treated with an oil that kills insect pests, and the second tree was left untreated. The sites were located across a variety of different urban Temperatures, and the water temperature was monitored at each site over the course of the experiment.

The Researchers tracked the growth of all 40 trees for two years. Growth was assessed in two ways: by measuring the circumference of each tree's trunk, and by measuring how much specific Grew branches on each tree. The Also Researchers measured each tree's photosynthesis, the which is how trees capture carbon from the atmosphere and is a key marker of tree health.The Researchers found that the scale insects and spider mites - well known tree pests - were more abundant at sites hotter. 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.