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I don’t just rely on fall color to tell me the seasons are about to change. There are so many other little things to observe that help me make the transition.
Gossamer webs floating in the air, the long shadows of a sun falling slowly in the southern sky, walnuts hidden in the grass, and robins flocking in search of crabapples and other fall fruit.
These are the signs of fall to me. They prove mostly comforting but also remind me that I need to get ready for the first frost and inevitable hard freeze, after which there is no turning back. Maybe we will have an Indian Summer, with a warm stretch in late October or November, maybe not.
No matter, the tropical house plants are taking up their winter residence in the sunny basement, most will be put on a diet of little water and no food so they can rest a bit through the short days of winter.
Orchids sit on my desk in the sun; I’ll wait for the emerging sheaths turn to bloom later in the winter. The holiday catcti and amaryllis will sit in a room that has natural light so they will set their buds accordingly.
But the thing that really steals the show this time of the year is, indeed, what we call fall. The senescence of foliage is a remarkable physiological response that marks part of the seasonal cycle for deciduous plants. Bernd Heinrich, in his book Summer World, discusses the likely evolutionary response to snow and ice load. Trees with broad leaves learned that shedding leaves in fall would reduce the damage that may occur in winter if there was ice and snow.
So for a very long period of time the art of senescence by deciduous trees was perfected to maximize the storage of food, refresh your foliage, and provide a rest up top while continuing to establish a stronger root system below. Plus all those falling leaves in the fall turned to organic matter, which the tree could snack on the rest of the winter. That’s sustainable.
So I have been waiting for the color to start draining from the leaves…it October, after all. But it seems that our pleasant summer may make for a delayed senescence. Those colors are there, they are just waiting for the green produced by chlorophyll to drain back into the tree for stored energy during dormancy.
Here’s what happens in the seasonal cycle of a tree: During the long days of summer trees are continuously replenishing their supply of chlorophyll, which uses sunlight and carbon dioxide to make food for the tree in the form of carbohydrates.
As the days get shorter and the amount of sunlight decreases, trees take what chlorophyll is left and drain it back into the tree for stored energy. As the chlorophyll drains from the leaves, the fall color is revealed.
What makes for the rainbow of colors underneath the mask of chlorophyll-green? Pigments called carotenids (yellow, brown and orange), anthocyanin (reds and purples) and a combination of the two create the dramatic reds, bronze and bright orange found in sumacs and oaks.
The carotenoid pigments are always present in the leaves, but the anthocyanins are produced later in the summer, triggered by cooler evening temperatures and shorter days.
More anthocyanins will be produced if this time period is warm and sunny because it allows for extra sugar production.
More sugar means more intense color and more sugar means more sun; so a late summer with clear sunny days and cool nights means more vibrant fall color. I am still thoroughly green here so I’ll be watching the robins, squirrels and spiders for my autumn correlation.