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Article #63, September, 2002
By Bill Cook

     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. 

     This year, the weather has brought plenty of rain and warm temperatures, although the cool, wet spring resulted in a strained start for many tree species.  For the most part, the forest had a pretty good growing season, which translates into the greater possibility of an exceptional color change; more sugar production can mean better colors.

     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 internal clock that trees use to drop leaves has little to do with weather.  Weather is far too unpredictable for trees to use as an indicator of seasonal change.  Itís 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 every species uses the same clock.  In general, itís 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 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.  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.  But itís a risky business 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 usually out-performs the color changes in other parts of the continent. 

    If you visit Colorado, sometimes residents will boast of their bits of golden aspen in the Fall.  They wonít be able to appreciate the snicker of we yoopers who know of brighter gold and larger expanses.  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.  Colorado has mountains, but we have the color and lakes. 

     But, let us not ignore the softwoods, or evergreens.  Although they do retain needles year-round, they donít 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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