Friday, September 21, 2007

Fall Colors

Nature Watch
September 21, 2007

By Susan Benson
Director of Education
Cable Natural History Museum

What good is phenology? For some, it’s a year-round hobby that helps keep them in touch with the ebb and flow of the natural world. But the practice of noting and recording seasonal changes in nature does have what some would call more practical values.

For example, phenology is used to help with the prediction of insect emergence and strategies for insect control. Farmers, of course, are phenologists, and carefully correlate natural patterns and seasonal changes with crop planting and harvesting. Scientists who study global climate change trends pay close attention to the history of phenological data.

This time of year, the most obvious seasonal change is literally right in front of our eyes, as we are at the time of peak leaf color change among our deciduous trees.

The appearance of the beautiful yellows, reds, oranges we see is actually a result of the fading of the leafs’ green color, which is caused by cholorophyll. When chlorophyll fades, “beneath” it are other types of pigments that become revealed. These are the carotenoids, which produce yellow, orange, and brown colors; and the anthocyanins, which produce red, purple, and crimson colors.

The vibrancy of fall color is related to weather conditions that occur before and during the time when chlorophyll in the leaves is dwindling. A series of warm, sunny days and cool, crisp, but not freezing nights seems to bring about the most spectacular color displays.

Different tree species have characteristic color changes. Oak leaves usually turn red or brown. Aspens transform into golden yellow. Red maples turn brilliant scarlet and sugar maples change to an orange-red. Leaves of some species, such as the elm, just shrivel up and fall, while changing to a drab brown color.

The timing of the color change also varies by species. For example, oaks show their colors long after other species have already dropped their leaves. The differences in timing among species seems to be genetic, for a particular species at the same latitude will show the same coloration in high elevations at about the same time as it does in warmer lowlands.

Unique among the color-changing trees is the tamarack, also known as the eastern larch. In the spring and summer the tamarack has bright green flat, soft, and flexible needles. They are shaped uniquely on the branch in a whirled cluster somewhat like a flower’s petals. The trees are easy to identify by their narrow pyramid shape and their location—they’re most common in swampy areas.

This tree is both coniferous (produces cones) and deciduous (loses its leaves). Although the tamarack looks like an evergreen, it is not ever-green, because its needles change to a golden-yellow color in the fall and drop off.

On warm and sunny fall days, garter snakes can be found basking in the sun on rocks and fallen trees. Soon, they will find a rock pile or an abandoned ant hill where they’ll spend the winter in hibernation. This snake’s yellow stripes help camouflage it in the grasses of forests and open fields where it lives. The garter snake feeds on insects and small rodents like mice. It is not poisonous.

About this time, northern flying squirrels begin visiting oak trees to feed on acorns. As the acorns mature you might find partly chewed ones on the ground. The squirrels feed at night, so if you want to see them, look for the acorns then keep your eyes open for squirrels scrambling up the trees.

Become a phenologist! Take a fall hike and note all the different colors of the forest. Gather wild apples and make your own applesauce or cider. Soak up the fleeting warmth of sunny fall days as we turn our thoughts to colder weather.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 43570 Kavanaugh Street or on the web at to learn more about exhibits and programs.

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