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This past summer was the third dry growing season in a row in the Upper Peninsula of Michigan. Stressed trees, especially red maples, began to change color early. However, most of the forest will proceed through the annual color change on schedule.

The timing is relatively consistent, as it is controlled by a balance between dark and light hours. This window is roughly ten days to two weeks from the end of September and into the first week of October.

Tree species comply, more or less, with their biological clocks, but not every species uses the same clock. The ashes go first. Oaks will persist longer. Trees along the Lake Superior shore have milder microclimates and often change colors at the end of the window. Forests on the shallow soils of northern Iron County are among the first landscapes to transform.

There is a lot of biochemistry related to the annual undressing of the forest. The process is part of what trees undergo to make themselves hardy for the cold and dryness of winter. Northern trees have some astounding and fascinating adaptations.

While timing is largely controlled by photoperiod, the intensity and visual quality of the fall colors can be impacted by weather. The compounds with red, yellow, and purple pigments may be brighter, or persist for a little longer, with warm days and frosty nights. But it's a risky business to predict color change patterns.

Should the first hard frost happen while the leaves retain good stocks of sugars, we should have a fine color show. Color intensity is a function of tree health and September temperatures. The drought may soften the intensity, but the difference will likely remain largely unnoticed.

Tree stress might also precipitate an earlier or quicker re-absorption of the green chlorophyll molecules. Red maples along our highways often cause comments about an early color change. These trees are responding to unhealthy growing conditions more than the onset of an early fall.

The geography and expansive forest of the Upper Peninsula provides some of the most colorful fall displays in the world. Annual treks by thousands of leafpeepers provide testimony to this fact. It is a good time to be in the woods, as bird hunters will quietly attest.

Most of our hardwood, or broad-leaf, forest consists of maples, aspens, and birches. We eagerly anticipate the crimson and gold of maples, which usually outperforms the color changes in other parts of the continent. Our aspens also turn a lively yellow color, especially with the right weather conditions. Birch are much the same way. A bright yellow canopy over a snow-white paper birch stand is an experience not soon forgotten.

But, let us not ignore the softwoods, or evergreens. Although they do retain needles year-round, they don't retain them all. The older needles, nearer to the trunk, fall off every year. The only exception is the glorious tamarack. Not only does it lose all its needles each fall, but it typically departs the season in a flaming blaze of gold! It is the last tree to change colors as the forest bids farewell to the growing season.

Once again, the much anticipated season of color change will soon lie behind us. This time of year, many of us hold our breath, lest we miss those few days when the forest canopy alights with the fire and brilliance of the last hurrah of the summer.

Every season hosts a multitude of changes in the forest and all that lives there, including us humans. Fall color is arguably the favorite of all seasonal changes and without doubt the outdoors is teeming with interesting events this time of the year.

Trailer
Bill Cook is an MSU Extension forester providing educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres. He can be reached at cookwi@msu.edu or 906-786-1575.

Prepared by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005 J Road, Escanaba, MI 49829
906-786-1575 (voice), 906-786-9370 (fax), e-mail: cookwi@msu.edu

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By-line should read "Bill Cook, MSU Extension" Please use the article trailer whenever possible.

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Last update of this page was 5 November, 2018