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In Da Woods

by Melanie B. Fullman, US Forest Service

Falling in Love

Walking through the woods these days is amazing! The colors, the smell of the leaves, the crispness of the air!!

Brilliant Survival Technique

Perennial plants, including trees, must have some sort of protection to survive freezing temperatures and other harsh winter conditions. Stems, twigs, and buds are equipped to survive extreme cold but tender leaf tissues are not, so plants must either protect their leaves or dispose of them.

Conifers, such as pines, spruces, cedars, and firs evolved with built-in protection. Their needle-like or scale-like foliage is covered with a heavy wax and the fluid inside their cells contains substances that resist freezing. Thus, the foliage of evergreens can safely withstand all but the severest winter conditions, such as those in the Arctic.

The leaves of broadleaved plants, on the other hand, are tender and vulnerable. These leaves are typically broad and thin, unprotected by any thick coverings. The fluid in their cells is a thin, watery sap that readily freezes. This means that the cells cannot survive temperatures below freezing. Tissues unable to overwinter must be sealed off and shed to ensure the plant's continued survival.

The Fall

In response to the shortening days and declining intensity of sunlight, leaves begin the process that eventually leads to their own ‘downfall’. As the veins that carry fluids in and out of each leaf gradually close, a layer of separation cells forms at the base of each. Once this layer is complete, the connecting tissues are sealed off, and the leaf can no longer stay attached to the tree. But before that happens…

Three factors influence autumn leaf color: leaf pigments, length of night, and weather. The timing of the color change and leaf fall is primarily regulated by the increasing length of night/shortness of the days. None of the other environmental influences – temperature, rainfall, food supply, etc. – are as unvarying as the steadily decreasing daylight. As the nights grow longer and cooler, biochemical processes in leaves begin to paint the landscape.

The amount and brilliance of the colors that develop in any particular autumn are related to weather conditions. The temperature and moisture that occur before and during the time the chlorophyll is dwindling are the main influences. The countless combinations of these two highly variable factors assure that no two autumns are exactly alike. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights usually produce the most brilliant autumn colors. A late spring or severe summer drought can delay the onset of fall color by weeks, and a warm fall often lowers the overall intensity of the colors.

Autumn Hues

During the growing season, chlorophyll is continually produced so leaves constantly appear green. As night length increases in the fall, chlorophyll production slows down and eventually stops; there is just not enough light or water for photosynthesis during the winter.

As each tree shuts down its photosynthesis factory, its green chlorophyll disappears. Other pigments in other shades suddenly become visible. They were there all along but unmasked by the lessening green-ness, the “new” colors can be spectacular.

RED & PURPLE anthocyanins are common in fruits such as cranberries, apples, concord grapes, blueberries, cherries, strawberries, and plums. They are water soluble and in trees, exist primarily in the watery liquid of leaf cells. Warm, sunny days and cool, crisp, but not freezing nights makes trees produce lots of sugars. But as the leaf veins close, the sugars are prevented from moving into the tree’s truck and roots. In the fall, trapped sugars tend to contain an abundance of anthocyanin pigments. The result is leaves in brilliant shades of red, purple, and crimson.

YELLOW, ORANGE, & BROWN colors are the result of carotenoids, which also occur in and provide characteristic coloring to corn, carrots, daffodils, rutabagas, buttercups, and bananas. Because carotenoids are always present in leaves, yellow and gold hues remain fairly constant from year to year, whereas reds and purples tend to vary.

In addition, certain colors tend to be attributable to certain species of trees. Oaks generally turn red, brown, or russet; aspen a golden yellow; and dogwood, purplish red. Red maple tends to be a bright scarlet; sugar maple, orange-red; and black maple, glowing yellow. Leaves of some species, such as elms, simply shrivel up and fall off, exhibiting little color other than drab brown.

The timing of the color change also varies by species. Oaks put on their colors long after other species have already shed. Such differences seem to be genetically inherited, for a particular species at the same latitude will show the same coloration at high elevations as it does in warmer lowlands.

Coloring in the Lines

Of course, you don’t really have to know a thing about carotenoids and anthocyanids to enjoy the peak of fall color, happening right now. Take a friend, a camera, and walk down just about any lane or street in the western UP or northern Wisconsin. Just go outside and relish autumn in the North Woods.

PS: don’t forget the FREE fall color tour (hike and Copper Peak ride) this Saturday, Oct. 1. Contact Jason Hofstede at 932-0845 to register or for more information.

See YOU in the Woods.

View More Photos by Bob Severin

Polar Bear Cookbook

Thank you to everyone who submitted recipes for the Polar Bear Hockey Cookbook. The cookbooks are now available. The cost for the cookbooks are $10.00 so make sure to grab one for yourself and maybe one or two as a gift. They can be purchased at the Pat O'Donnel Civic Center concession stand or by contacting Kerry Roehm or Micki Sorensen.


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