PARTS OF NORTHERN Dickinson County already are showing considerable amounts of fall color, with the peak for the entire county expected next week. (Betsy Bloom/Daily News photo)

The Upper Peninsula’s annual fall color show is under way.

According to the Upper Peninsula Travel and Recreation Association website at www.uptravel.com, as of Sept. 26, 10 to 20 percent of the foliage in Dickinson County had changed color, with the peak expected next week.

Iron County is farther along, with 25 to 40 percent color change and the peak predicted this week.

Menominee County reported 10 to 15 percent color, Delta County 10 percent, with peak for both anticipated to come the second week of October as well. Marquette County has 15 to 35 percent change and should hit peak this weekend.

Bill Cook, a forester and biologist for Michigan State University Extension, said this year’s growing season was good, with equal periods of rain and sun.

“Frost brings out vibrant colors,” Cook added, “but then it could accelerate the process. We cannot predict nature.”

Leaves usually change color with the seasons, but a few factors can affect how vibrant the annual display turns out. Leaf color can be influenced by the stress of the tree, September temperatures, micro-climates and soil.

Lake Superior’s milder micro-climate holds trees in a state of summer longer, so leaf color may change later within the season. Northern Iron County has more shallow soil, so trees there tend to turn earlier.

A lot of biochemistry goes through a northern forest in preparation of winter’s cold temperature and dry air, Cook explained. Besides the amount of light, weather also determines the leaves’ vibrant color. Leaf compounds with red, yellow and purple pigments may be brighter, or last longer, with warm days and frosty nights. A hard frost can determine the output of color, if the frost times correctly with the amount of sugar in the leaves.

Chlorophyl is responsible for trees and plants turning sunlight into nourishment. The dominant green chlorophyl, of the leaf “covers up” the autumn color pigments that are seen in the fall. As the light of the day shortens and temperatures cool, chlorophyl breaks down, revealing the autumn colors. When chlorophyl breaks down, anthocyanin is created. Anthocyanin is known for making the leaves red. Xanthophyll is the chemical in the leaf that provides the yellow color. Carotenes create the bright orange color of the leaf.

The trees then turn to stored sugars to survive the winter.

In the Upper Peninsula, most hardwood forests are comprised of maples, aspens and birches. Maples are known for their red and gold leaves, while aspen and birch show a brilliant yellow, when the weather conditions are right.

The softwoods, or evergreens, also go through a metamorphosis, though not as noticeable. Older needles fall to the ground. The tamarack goes out with a blaze of gold before losing all its needles. It also is the last tree to change for winter between October and November.

Cook advises walking the forest trails this time of year. “Bugs are gone, no heat, and there’s a lot of activity in the woods,” Cook said.

For those who want to view from the comfort of their vehicle, www.uptravel.com lists 10 fall driving tours that range from west to east, north to south, and cover every county in the Upper Peninsula. Fall tour No. 5 is 125 miles and goes from Escanaba to Iron Mountain by way of M-35 South (Escanaba – Cedar River – Menominee), U.S. 41 North (Menominee – Spalding) and U.S. 2 west (Spalding-Norway-Iron Mountain).

“The fall tourist season is very good so far,” said Tom Nemacheck, executive director of the Upper Peninsula Travel and Recreation Association. “October is a great time to get out. A lot of leaves are still green, so there will be a lot of color coming yet.”