Autumn is no doubt called “fall” because it is when trees drop their leaves and show us how beautiful it can be to let go. Those leaves often turn from green to shades of red, yellow or brown prior to their fall. This colorful display of foliage usually begins in late September and continues throughout October.
Many of those colors have actually been present in leaves during the entire growing season but masked by chlorophyll, the light-absorbing green pigment that is essential for photosynthesis.
When days shorten in the fall, photosynthesis slows and eventually ceases causing deciduous trees to stop making chlorophyll, allowing other pigments in leaves to become visible. Carotenoids are the pigments responsible for yellows, oranges and browns; anthocyanins create reds and purples; and mixes of the two pigments result in bronzes and deeper shades of orange.
Location, weather, and type of tree determine when this color change takes place. Cooler locations are where the transition begins, causing trees in northern Minnesota to change color before those in the south. In the Twin Cities, peak fall color usually occurs in the first or second week of October. However, timing can change from year to year, influenced by temperature and rainfall. Drought causes less brilliant colors and trees in dry years drop their leaves earlier. At any one location, fall colors typically follow a sequence determined by tree species. Ashes are known for their early color change. Aspens, cottonwoods and maples often follow, and oaks change color later. Conifers, of course, don’t change color or drop their needles – except for tamarack (also called larch), the only conifer in Minnesota that changes color (from green to yellow) and drops its needles in the fall.
Fall foliage isn’t the only impressive natural event in Minnesota during October. Waterfowl migrate through the state in large numbers and there are many good locations for seeing these birds. Ducks and geese are excellent subjects for beginning birders since they often are easily seen on open water, unlike small songbirds that can be hidden behind leaves, and most have distinctive field marks and behaviors that can be quickly recognized with practice. Grab a field guide and binoculars and look for waterfowl at locations such as the Conservancy’s Seven Sisters Prairie that attracts large numbers of canvasback ducks to Lake Christina. Wetlands that attract waterfowl often attract other impressive birds, including sandhill cranes, one of the largest birds in the state. Thousands of cranes stop at Sherburne National Wildlife Refuge during migration in the fall – an event celebrated with public crane tours throughout October at the refuge. Watching flocks of cranes and hearing their bugling calls is an October experience not soon forgotten.
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