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The Autumn season has certainly begun, even though we still have warm days, most of the leaves remain green, and the sun has not quite yet migrated south of the equator. But, the geese are moving, the gardens are producing, and most plants and animals have begun their annual preparation for the winter.

The usual vanguard of stressed trees began their color change in August. Red maples in the swamp have gone scarlet. Individual aspens, black ash, sugar maple, and other species that logged a poor season are checking out early. But the bulk of the trees will turn during the end of September and into October. The leaf-peeper season is just around the corner.

Despite the droughty summer and first frosts, the internal clock that trees use to change colors has little to do with weather. Weather is far too unpredictable for trees to use as an indicator of seasonal change. It’s the photoperiod. The relative number of hours of light and dark in a day.

Tree species comply, more or less, with their biological clocks, but not everyone uses the same clock. In general, it’s the photoperiod that affects the timing of leaf drop, not nut crops, or woolly bears, or bird migrations.

There is a lot of biochemistry related to the annual leaf drop. 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. Tree stress might precipitate a more effective or quicker re-absorption of the green chlorophyll molecules. The compounds with red, yellow, and purple pigments may be brighter, or persist for a little longer. Frost can also have influence on the quality of Fall colors, too.

This year, many trees were forced into producing a second set of leaves. A variety of insects munched away at the forests and many of us will remember the forest tent caterpillar for years to come. While these are normal occurrences in the life of a forest, the stress may contribute to an earlier Fall color change in some parts of the Upper Peninsula. But it’s dangerous to predict color change patterns.

Most of our hardwood, or broad-leaf, forest consists of maples, aspens, and birches. We eagerly anticipate the crimson and gold of maples, which pretty much knocks the socks off 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 to this 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!

Every season hosts a multitude of changes in the forest and all that lives there, including we 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. What new things might you discover hidden amid the kaleidoscope of Fall?

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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

Use / reprinting of these articles is encouraged. Please notify Bill Cook.
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