Potentially warm fall may mean long-lasting color
But expert also says drought could cause trees to lose leaves early
Chlorophyll has begun to break down in this leaf, revealing pigments such as carotenoid and anthocyanin. (G. Randall Goss/News-Review / August 31, 2012)
Lucky for our residents, those deaths will result in a brilliant landscape of color.
"Here's basically what happens: as the sun angle goes down in the fall, a tree's leaves lose the ability to make food," said Scott Rozanski, meteorologist for the National Weather Service in Gaylord. "It's like when you take a rubber band and put it around your finger. Eventually, it'll turn black and fall off. Leaves do the exact same thing."
This lack of sunlight turns leaves hard and brittle, said Rozanski, "almost like they're suffocating, in a way."
"It's just a fact of the sun angle going down. The only thing that can change that or make that premature is if you get a couple of really hard freezes in September. Water droplets freeze and burst, which kills the leaf and it falls off," he said.
And as fall progresses, trees begin to recycle some of the chemicals in the chlorophyll in their leaves — the chemical responsible for photosynthesis, said Bert Cregg, associate professor of horticulture and forestry at Michigan State University.
"As that happens, other pigments, some of which are already there, increase in production," said Cregg.
The pigments that already exist are carotenoids and anthocyanin. Carotenoids make carrots orange, and anthocyanin give the eggplant its deep purple skin. In trees, carotenoids show up in the yellow and orange leaves of red maple and sassafras and anthocyanin gives a purple hue to ash and oak trees.
The chemicals are present in different amounts in trees, which typically change color in the same way each year.
"Because of species and genetics, or whatever it is, year after year we have those standouts," said Cregg, describing a trail near Lake Lansing he walks. "It's completely covered with red maple, which have yellow leaves. It can be a cloudy day, but you feel like you're walking under sunshine."
Cregg says, after the March heat wave, April freezes and summer drought, Michigan's trees are stressed and have begun to scorch and drop leaves already — near Lansing, sumac were bright orange in July.
How bright the colors are and how long the leaves hold on depends on weather.
Rozanski says we could be in for a wet, mild fall. The El Niño pattern is developing in the Pacific, building from warm temperatures over the Equator in the Pacific. The pattern usually builds until Christmas.
"Generally, that means we will have a very wet fall and a mild rest of the winter, but right now, it's still in its development page," said Rozanski.
That means every weather prediction right now is just that: a prediction, and full of caveats.
"Because when you have an El Niño, there's only one guarantee: if it's extremely warm, it will be mild and we may have very little snow," said Rozanski.
Still, he said, "mild" for Michigan could mean three degrees above our winter high temperature of 28 degrees, and an above-normal temperature doesn't mean a lack of snow. Rozanski predicts about 120 inches of snowfall.
"I would guess we'll be 20 inches below normal, only because El Niño will keep us a little more mild. So earlier November will probably end up being rain," he said.
People consider the best weather conditions for fall color to be mild, clear days and mild nights, though the need for there to be clear days might just be a perception.
"Cool, clear days and cool nights just might affect our perception. The colors might be the same as a gray, dreary day," said Cregg. "But when it's 72 degrees and sunny, the colors really stand out."
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