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Nature Notes 6- Autumn Leaves October 14, 2020
Our current topic: Autumn leaves
Football: a sure sign of autumn. Well, maybe not in 2020. Let’s go with Plan B: the leaves changing colors.
Everyone knows this happens, but that’s where many folks reach the end of their knowledge about the event. Let’s explore. Two main factors cause this event to occur: 1) falling temperatures, mainly at night, which can vary a great deal from year to year and by location (elevation); and 2) decreasing sunlight each day, which will NOT vary from year to year. This combination will cause a layer of tissue at the base of the leaf stem (called the abscission) to dry up and stop the flow of water and nutrients into the leaf and the outward flow of “food” to the rest of the tree. As this occurs, the green pigment (from the chlorophyll in the leaf) disappears, and the human eye starts to see the yellow (xanthophyll) and orange (carotene) pigments that have been in the leaf all along. The color or shade of color produced can vary a great deal based on such things as the amount of rainfall in the weeks prior to temperature and sunlight changes, and the speed of the temperature change. A big part of the color you see is based on the species of the tree. Have you noticed the species of the trees when you looked at fall colors? Red maple, Scarlet oak, Sassafras, Black gum, Dogwood, Sumac will always be some shade of red. Tulip poplar, hickories, other maples, birch, will be a yellow or orange of some kind. Oaks (other than Scarlet), Sycamore, Beech, usually produce a brown leaf, ranging from golden to dark brown. With the intermingling of species and conditions, the color combinations seen within the forest can vary greatly each fall. Toss in the green of the evergreens and a few other trees that don’t change and the forest is full of colors to enjoy. But don’t count on a long time to enjoy it. Once that layer of tissue dries up, wind or rain will quickly strip the leaves from the trees and deposit them on the forest floor. However, some trees, mostly oaks and Beeches, have a tendency to retain their leaves much longer. Something to note on your late winter hike is leaves on the forest floor. In a mixed stand of trees, most of the leaves you see will be oak leaves even though maples, hickories and other species will be overhead. Why? The other species fell first and are now covered by the late-falling oaks. Dig under the oaks and look for other partially decayed species. Also the chemical make-up of the leaves is different by species. The oaks contain a higher amount of tannin than other species, and that delays the decay.
So now, plan your autumn hike and look for what you have read about above. Note when the leaves start to change and by species. Note the color creep down the mountain sides as the lower elevations become cooler at night. Collect some leaves and see if you can identify them. If it is winter or early spring, dig down and see what leaves, or pieces of leaves, you find. Find any nuts or acorns? Find any little critters? We’ll talk about what this layer is and does in a later note.
Get out on that hike and start looking at nature. It’s not hard to find. Hopefully, these notes can help you understand what you see and how you see it.