- Associated Press - Saturday, October 25, 2014

JEFFERSON NATIONAL FOREST, Va. (AP) - Virginia Tech tree scientist John Seiler takes a class of dendrology students to Pandapas Ponds near Blacksburg, showing the same trees he’s visited like this for each of the past 33 years.

Occasionally he stops, points to a plant and says quiz time. The students on the Oct. 14 trip turn to their clipboards and give their best guess at what species it is.

Seiler has the kind of tree-centered mind that can look at a sugar maple this year and remember how different its fall colors looked on the same day several years ago.

“Most years are much better than we remember them,” he said. “You know, it averages out pretty good. What causes them to be crappy is the peak weekends being during bad weather. So it’s the peak and (storming outside), nobody’s taking a drive. So everybody is like, ‘Boy it really stunk this year.’ But when I go back to these same areas year after year and I’ve got to go whether it’s raining or not, there’s good color every year.”

Seiler has a passion for trees. He’s been studying them for his entire career and he is one of the creators of the leading tree identification smartphone app.

With about 150,000 downloads since 2011, VTree is used all over the country by amateur hikers, tree experts and outdoor enthusiasts. It uses the phone’s GPS to determine what trees grow in the area where you’re standing, then asks a series of questions to narrow down the list. Eventually, it will identify exactly which tree species you’re looking at.

“So this thing turns into an innumerable number of books,” he said. “It literally becomes the trees of anywhere.”

Seiler said there is a lot of folklore about what makes a good or a bad foliage season, but even experts don’t have it all figured out. Like all things in nature, those beautiful fall colors follow certain scientific principles.

The foliage season begins as winter approaches and days start to get shorter. Some of the chemicals in tree leaves detect the number of daylight hours, Seiler said. As the number decreases in the fall, the chemicals reach a trigger point and set off a series of chemical processes. The threshold is different for each species, but eventually all trees start to get ready for winter.

Leaves always contain the yellow pigment, Seiler said. The color is there even in the summer, but it’s overwhelmed by the vast amount of chlorophyll, which makes the leaves appear green.

Chlorophyll is full of important nutrients, so trees break it down and reabsorb the nutrients as they get ready for winter.

“It just wants to reabsorb all that nutrients,” Seiler said. “It already has them, it reabsorbs them and stores them for the winter. So a green leaf falling on the ground would be really stupid. It took a lot of energy to build those things, so it reabsorbs it all.”

As the chlorophyll exits the leaves, the yellow coloring - which has always been there - starts to show through.

For some species, this is as far as it goes and yellow is the only color its leaves will display. But other trees are capable of producing another chemical that turns them red.

Seiler said scientists aren’t quite sure why some trees make this red chemical and others don’t, but the going hypothesis right now is that it acts as sunscreen to protect the plant as it reabsorbs chlorophyll.

Even on the same branch, leaves that are exposed to direct sunlight will turn red, while ones in shade “don’t need sunscreen, so they don’t put it on.”

“It’s not all figured out,” Seiler said. “What they do know is that when you take leaves that turn red but they’re in the shade, they won’t turn red. In fact, you can put a sticker on a leaf, you peal that sticker off and it will just be yellow under the sticker.”

Orange is made by mixing yellow and red, which explains why many leaves are orange. Purple looking leaves are really just very dark shades of red, Seiler said.

He said some other environmental factors can affect foliage, too, but to a lesser degree. A drought, for instance, can cause leaves to develop less of the red chemical and fall off the tree earlier. But Seiler said the length of the day has the greatest affect on timing of the peak, and the amount of sunlight as leaves start to turn yellow determines coloring.

“That’s why clear days - sunny, bright, clear days - in the fall when all this is taking place lend leaves to greater red development. So yes, sometimes clear, bright, sunny days give better fall coloration. That’s really only for the red pigment. If we have a lot of (cloudy days), that can slow down some of your red formation.

“You can see it if you start looking around. Like sugar maples, the leaves in the interior just kind of turn a yellow and the leaves on the outside get the deep oranges and red. . That’s why a lot of those species sort of have every color of fire, everything from yellow to red, depending on how much is being formed in the red.”

The timing of the peak can shift around a little, but he said it’s always centered on the third week of October. Sometimes, like this year, it will come about a week before, and other times trees will peak around Nov. 1.

Once a leaf starts to show yellow, Seiler said, it will be brown and waiting to fall off within about two weeks. So, by his estimate, many trees throughout the region will be brown by Oct. 25 this year.

“People always brag about New England,” Seiler said. “New England has got, basically, just sugar maples to look at. And they’re famous for it. But that’s it. Here, we’ve got some of the highest diversity for eastern forest, so it allows us to drive around and there’s a yellow one and there’s a red one and it also makes it go a little longer.

“It’s great here in the Appalachians because of all the different species. They’re not all timed the same, but it makes it go a little longer.”

___

Information from: The Roanoke Times, http://www.roanoke.com

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