By Jim Poling Sr.
The lights dim. The audience turns to other spectacles.
Nature’s annual autumn show is over. It was a spectacular one. Certainly one of the most vibrant in years. Crimson and golden hillsides seemingly competing to take our breath away.
There are many theories on why the autumn leaves were so dazzling this year. People cite drought, followed by ample early autumn rain. Others say low night temperatures, but without frost, are responsible.
Weather factors such as temperature and moisture do influence leaf change, but research tells us the most important influence by far is the calendar. Shorter hours of daylight and longer dark and cool nights set off biochemical processes that cause leaves to change.
No one really knows everything about why trees act the way they do each autumn. Not even the scientists who study these things.
We do know what causes trees to abandon their healthy green foliage. In spring and summer trees produce green chlorophyll to help them convert light into chemical energy that results in sugars and starches. This is all part of a food production process known as photosynthesis.
In the fall, green chlorophyll production slows, allowing reddish-orange carotenoid pigments and red to purplish anthocyanin tints to appear.
The reds and maroons displayed by sugar maples, sumac and some other tree species are derived from anthocyanin pigments formed from sugar stored in the leaves. The yellow to golden orange hues of birches, aspen and hickory come from carotene chemicals that give colour to corn, carrots, pumpkins and egg yolks.
But we know nothing about the reason why trees change their colour. What are they trying to achieve?
“This is both surprising and puzzling, since Nature seldom wastes energy to no purpose,” writes James Poling (no relation), author of Leaves: Their Amazing Lives and Strange Behavior. “Yet as far as botanists can determine, the chemical energy that goes into the painting of a leaf is of no benefit at all to the plant. The colors seem merely to herald the end of a leaf’s life cycle.”
There are some theories about why trees change their leaves, but none scientifically proven.
One is that the change in leaf colour is a warning to insects such as aphids who want to burrow in trees for winter. If leaf colours indicate chemical defences are present, then insects will avoid the tree.
Then there is the theory of photoprotection in which anthocyanins protect the leaf against the harmful effects of light at low temperatures. Supposedly this allows the leaf to live a bit longer.
Then of course there is a longstanding belief that trying to maintain photosynthesis during the low light, cold, high winds and snow of winter is just not worth the effort for trees. So they decide to take a winter break and drop their leaves.
Or, crazy as it sounds, are the trees doing it for us?
Studies show that fall colours can lift our moods. Some psychiatrists advise patients that a walk or drive through the autumn woods is therapeutic.
The contrasting colours of autumn leaves stimulate the mind. They are an exciting transformation after months of seeing just the bright greens of spring and summer trees.
Autumn colours signal the brain that change is happening. And, change can be exciting, even inspiring us to do different things – like taking up a new hobby or setting goals.
They are a reminder that change must happen before new things can begin. And, of course, a reminder that nothing lasts forever.
All said, I suppose it doesn’t matter that we know what purpose a tree has in changing the colour of its leaves. Time spent trying to figure that out probably is better spent just relaxing by taking in the fall spectacle.
Watching the leaves turn is a great reminder of how lucky we are to have four seasons and the beauty and differences that each brings.
Autumn, despite its signals of harder times ahead, is for many folks the absolute best of the seasons.
I like the way autumn is described by Winnie the Pooh, author A. A. Milne’s fictional teddy bear.
Autumn, says Winnie, is “a time of hot chocolatey mornings, and toasty marshmallow evenings, and, best of all, leaping into leaves!”