The fall leaf season was approaching peak color in the Great Lakes Region on October 2, 2013. The Moderate Resolution Imaging Spectroradiometer (MODIS) flying aboard NASA’s Terra’s satellite acquired this true-color image of the region ablaze with autumn hues at 16:25 UTC (12:25 p.m. EDT) that same day.
The most brilliant and deepest colors appear in the forests surrounding Lake Superior, which lies in the northwest corner of the image. Oranges and yellows paint a swath across Michigan’s Upper Peninsula on the lake’s southern border, and in Ontario, Canada, especially in the woods near Sault Ste. Marie. That city can be seen as a gray smudge on the northern side of the black borderline, and on the northern side of the St. Mary’s River. On the southern side of that river sits Sault St. Marie, Michigan. By driving over the International Bridge which joins the two cities, dedicated leaf-peepers can easily take in the best of the autumnal display in two countries with just a few hours’ drive.
All deciduous trees sport green leaves in the summer, because of the presence of large quantities of the green pigment call chlorophyll. As the weather cools and daylight shortens, a layer of tissue grows at the base of the leaf, cutting off the supply of nutrients and water in the leaf. As nutrients diminish, chlorophyll breaks down quickly, exposing the colors of other pigments within the leaf. Because each tree species contains typical pigments, each species also typically turns a predictable color in fall.
In these northern forests, the aspen, sugar maples, birch and beech, which contain carotene, turn bright yellow, while hickory leaves tend more towards gold and bronze. Red maples, sumac and many oaks contain the pigment anthocyanin, which provides orange and red fall foliage. The amount of sunlight also plays a role in fall color as well. For example, anthocyanin isn’t as chemically active when sunlight is low, so leaves tend more towards orange or yellow in lower light.