Fall colors the world in yellows, reds, oranges. Many trees, shrubs, and most other plants trade their greenness for those vibrant colors in certain parts of the world. But why do leaves change colors? When and where do these kaleidoscopic color changes best occur. In this blog story, I'll try to cover the whys, the where, and the when of fall foliage color.
When and where to see the peak of Fall foliage?
In most cases, the "when" and the "where" are very closely connected.
Places in Canada, Europe and Russia near the Arctic start off the succession of Fall colors. In these places, fall foliage starts as early as September.
For areas in Europe, Asia, and Canada farther from the Arctic, they start their color changes in early October.
Along the Canada-US border Fall foliage peaks first to second week of October. Then a couple of weeks later, those in central USA see the Fall colors at their best.
Southern states of the USA may see the peak of Fall color in November.
You see, some magical painter waves its color wand from north to south where colors of leaves change.
We are blessed to vacation in Quebec when the Fall foliage starts in early October. It should have peaked. But this year the fall foliage comes a couple of weeks later. The September and October weather this year has not been cold enough to send the plants packing the greens in exchange for the vibrant colors of Fall.
As we continue our trip to Atlantic Canada, we witness the color changing in the region as well. Then as we close our vacation in southern Atlantic USA, we get to see the magic of Fall foliage in the places we visit. What a coincidence!
Why the change in colors
Foliage color change is all about adaptations and survival, as it turns out.
Trees and shrubs change leaf colors as they prepare to become dormant. Plants sense signals to get ready for less friendly plant-world weather that’s coming.
You know: shorter days and longer nights. Colder daytime temperature, and frigid night temperature. Cold rain and blustery wind. If you’re a plant you won’t like these either.
Plants temporarily shut down many of their functions to protect themselves from altogether running out of energy and nutrients when a long winter might plunge the plant world into a frigid wasteland. Otherwise, they might not bounce back in Spring. The color change is simply part of their road to dormancy and a way to survival.
Plants throughout the world undergo dormancy to get through bad times – going dormant is an effective tool for survival.
It’s like when we people run low on food and other basic supplies for whatever bad reason, and we fear things are not going to get better soon.
Think: powerful and disastrous typhoons or hurricanes, widespread fire, long droughts, floods, pestilence, Covid-19 pandemic, or worse, war.
What do we do in times like those? We stock up on meat, eggs, canned goods, and other food supplies and drinking water and candles. We hoard toilet paper. We slow down, and even try to rest and sleep more to conserve what little resources we have left. If need be, we remain indoors and some even hide in bunkers. Other members of the Animal Kingdom, like bears, squirrels and chipmunks, snakes and many other animals big and small, hibernate.
Yes, it’s all about adaptations and ultimately survival.
Plants do the same. They’re even in a worse situation than humans, because plants can’t move, can’t drive, can’t gather food, and can't get water whenever they want to. They simply rely on Nature and on what they already have, not on what they could have.
It's all about the chemicals in the leaves
With less chlorophyll l (green pigment) due to less sunshine and lower temperature, leaves turn yellow as xanthophyll (yellow pigment) becomes the dominant pigment.
Over time, leaves fall off to reduce water evaporation.
As daylight shortens and temperatures plummet, plants reduce making chlorophyll.
Chlorophyll is the green pigment or chemical that powers photosynthesis. Photosynthesis provides plants with their energy (sugar). But they need sunlight to do that. Without much sunlight, photosynthesis drains more energy than it creates. So plants reduce, then even stop production of chlorophyll in Fall and into Winter.
As the green chlorophyll drains away from each leaf, other pigments in the leaves start to show their colors: reds, oranges, and yellows.
In response to the shorter days and less intense sunlight, leaves begin the processes leading up to their falling off right off by early Fall. The veins that carry fluids into and out of the leaf gradually close off as a layer of cells forms at the base of each leaf. Much like humans creating a scab when we get a cut. These clogged veins of leaves trap sugars in the leaf and promote the production of anthocyanin, a red pigment in leaves. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall off. And most shed off their leaves in abandon.
Awesome display of fall foliage at the Acadia National Park in Maine
When chlorophyll (green pigment) is produced less in leaves at the end of summer, xanthophyll (yellow pigment), carotenoid (orange pigment), and anthocyanin (red pigment) start to show up more prominently. Thus leaves turn yellow, orange, or red at the start of Fall.
Effects of temperature, sunlight and rainfall
Warm, sunny days and cool, crisp but not freezing nights at the start of Fall seem to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual clogging or closing of veins going into the leaf prevent these sugars from moving out.
These conditions – lots of sugar and light – set the motion for making brilliant anthocyanin pigments. Anthocyanins tint reds, purples, and crimson.
The yellow pigments, the carotenoids, on the other hand, are always present in leaves. So the yellow and gold colors remain fairly constant from year to year. You see this when leaves start to die out and turn green to yellow before the leaf dies, even in Summer. Even in the lush and tropical countries, plants' leaves turn yellow, then brown, then blacken when they're dying off.
Fallen leaves feed the cycle of life of trees as the leaves later decompose and become part of the plants’ nutrients the following growing season. For science-inclined gardeners, the colors of the fallen leaves indicate the timing when the leaves had fallen off.
Leaf abscission (the fancy technical term for the dropping of leaves) begins with the degradation of chlorophyll. As the green fades, yellow and orange pigments known as carotenoids are revealed in the leaves of many species. After showing off their glorious Fall colors, the leaves fall off. Fallen leaves eventually decay and become part of the plants’ nutrients the following growing season. The Cycle of Life in Nature. Nature supports itself.
More importantly, the shedding of their leaves conserves whatever little water is stored by the trees and plants. Plants lose water mostly through their leaves. No leaves, minimal loss of precious water. Smart move.
The weather all through the year can affect the Fall color season, too. Temperature affects the rate of chemical reactions in leaves. Sunny autumn days are needed for the brightest color displays since anthocyanins require light. Overcast days will lead to more yellows and browns.
This year, for example, a warm spring was followed by a hot and rainy July but cooler than normal August. Some trees reacted to the variable stress of prolonged heat by starting dormancy early, dropping their leaves over the summer. Yet August was warmer than usual so most trees in our area changed their colors a bit later.
Yellow green (combined carotenoids pigment) creates artful foliar displays
In general, the Fall foliage color show is most grand when late September and early October bring adequate rain, sunny days, and cool nights. A hot or dry September can make the Fall colors early but muted.
The red pigment, anthocyanin, which typifies fall color is produced only by some tree and shrub species. The amount they produce varies by species and depends both on that year’s weather and the circumstances in which the tree is growing. The more sun a tree gets, the more anthocyanin it makes, giving a fiery red and brilliant reddish-orange display.
Red and orange leaves indicate more production of anthocyanin, good sun exposure, and longer warm temperatures.
I’m sure you are keenly aware that at the start of Fall, leaves transform from lush green into fiery reds and resplendent yellows and shades of oranges, offering us a kaleidoscope of colorful masterpieces. It’s as if the plant world is staging an impassioned, dramatic performance or creating masterful strokes of painterly colors.
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