22 September 2009

Reasons for late fall colors

After a long hot summer, fall colors are just around the corner. Or are they? With fall arriving today, folks want to see the bright reds, oranges, and yellows, but those fall colors seem to show up later and later.

The culprit for these late arrivals is increasing amounts of carbon dioxide in the atmosphere for prolonging the growing season of trees, scientists said.

“Carbon dioxide fools the trees,” said Wendy Jones, a research associate at Michigan Technological University, who conducts research at the Aspen FACE site in northern Wisconsin. “They think they should still be growing when they ought to be going through autumnal senescence”—changing their colors and settling down for a long winter’s nap.

The phenomenon first appeared at the Aspen FACE (Free Air Carbon dioxide Experiment) site in Rhinelander. Plots of trees underwent exposure to varying levels of carbon dioxide and ozone to gauge how increasing concentrations of greenhouse gases will affect northern forests.

Delaying the color change may actually be good news for forest products industries. If that occurs, it could mean trees will become a bit more productive due to the extra carbon taken up in the autumn, along with the increased photosynthesis throughout the growing season.

Jones cautions other variables also affect tree growth and senescence, however. In other words, even with higher levels of carbon dioxide, the annual autumn spectacle could still come early. “It’s been a dry year here,” she said, which generally means trees lose their leaves earlier.

For related information, go to www.isa.org/environment.