Fall Phenology

By Susan Thurn,
CNHM Director of Education

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 nearing the peak of 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 leaf’s 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.

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 swamp and bog 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.

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.

For over 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 and new exhibit, On Lake Owen: The Art of Walter Bohl, in Cable at 13470 County Highway M. Also find us on the web at www.cablemuseum.org to learn more about our exhibits and programs. Post your own stories on the Nature Watch blog at cablemuseumnaturewatch.blogspot.com.