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The Process that Turns New England Into a Color Wonderland
By James H. Hyde
It's hard to nail down what makes the fall such a pleasurable season. Perhaps it's the fragrance of smoke wafting from chimneys and mixing with the scent of the last cutting, the harvest, or the fresh, chilly air.
Or maybe it's the promise of snows to come and the coziness of a down comforter on a cold, autumn night. Or maybe it's the simply the awe-inspiring, majestic colors.
Looking at all of those features makes me think it's all of the above and that the absence of any one would deprive us of the awesomeness we've come to expect each year.
But what is it that triggers the leaf-color-change process?
How the Color Change Process Works
Through the process of photosynthesis, the leaves, at least in part, helped to make the tree's food, only to have trees deprive the leaves of chlorophyll (what makes them green and helps the tree produce glucose), force them to produce stark, luscious colors, break away and become the next layer of soil on the forest floor.
As we know, the color change is a phenomenon unique to deciduous forests and some evergreens, a healthy mix of maple, birch, poplar, redbud, elm, sugar maple, evergreens, sumac, oak, dogwood, hickory, sweet gum, black gum, sourwood and ash trees.
Which Tree Leaves Turn Which Color?
Leaf colors are determined by the tree's genus. For instance, the evergreens, spruce, fir trees and rhododendrons and laurel, among others, are evergreens. Even though some species will change the color of their leaves and let them fall, what remains at season's end stays green.
Birch, elm, poplar, redbud and hickory trees give us the gold and yellow hues that seem to dominate as the backdrop for the reds in autumn's color scheme.
Red oak, hickory, ash, sugar maple, sweet gum, black gum, sourwood, red maple, as well as dogwoods give us the stunning red, deep magenta and purple colors, although they can produce yellow leaves. We get maroon from sumac.
Why and How Do Leaves Change Color?
Knowing which tree produces which color is one thing. The big and growing question over the years has been why and how they change? The most popular belief in scientific circles holds that as the days grow shorter and the nights longer and cooler, the leaf color change is triggered.
The process begins with the severance of chlorophyll to the leaves and clothing them in their inherited colors before they fall off and glide to nature's woodland carpets.
As with all things scientific (or botany-related in this case), theories conceived by the specialists exist with slightly different spins on the phenomenon that visits New England and other parts of the country each year.
Without plants, trees in particular, I wouldn't be keyboarding this story now. They are nature's carbon dioxide scrubbers and oxygen providers. As we inhale, we're breathing in oxygen produced by plants and trees. Our blood is oxygenated in our lungs and it then carries the oxygen to our tissues. What gets exhaled in that process is carbon dioxide.
If that builds up to certain levels, it can be fatal in humans, so trees feed us the life-nurturing gas we need to breath and protect us from harmful gases that could imperil our lives.
During the process, water is taken from the soil by the tree's roots and carbon dioxide from the air by the leaves. Sunlight then converts both water and carbon dioxide into glucose, a natural sugar, which becomes food for trees.
The catalyst for all this is chlorophyll. Under the green of tree leaves that produce yellow fall flora lays a yellow pigments that gives the leaves their yellow, gold and orange colors.
Some scientists conclude that the whole leaf isn't completely yellow under the green, but rather exists in small patches that spread in the fall. Others maintain that what we see in autumn is just as prevalent in July, but lies hidden under summer's green tints.
During the summer, some of the tree's food (glucose), is stored for winter reserves. When summer ebbs, the days get shorter, and with shorter days and longer, cooler nights, trees are able to decrease or cease food production and stop the flow of chlorophyll to the leaves. That eliminates the green color.
In contrast, the leaves that give us the deep red and magenta colors appear only in the fall when the temperature ranges between freezing and 45 degrees and the trees have plenty of sun. Red pigments aren't "under" the green in the leaves as are the yellow-leaf genuses. Instead, some of the glucose produced when the tree manufactured its food is trapped in the leaves and when the chlorophyll disappears, the glucose reddens because it contains a red pigment.
In the case of the oak tree, the process is decidedly different. Oak leaves contain waste from the tree, so they turn brown before falling to the forest floor.
While leaf color is determined by tree type, color saturation, or how bright the hues become is affected by how cool and sunny fall days are. The cooler and sunnier, the brighter the colors. But summer weather can play a role as well. If there's too much or too little rain, for instance, the colors may not be as bright during the peak period.
What Role Does Weather Play in Color Saturation?
The biggest determinants of how deep the hues will become are water and air temperature.
Frosty nights that stay slightly above freezing, and sunny fall days are responsible for color depth. Leaves turn much brighter under those conditions.
In the case of trees that yield yellow leaves, ever present are the yellow tints that lie beneath the green and emerge as all yellow, orange or gold in the fall. In the case of red leaves, ideal weather produces radiant reds, magenta and sometimes purple leaves.
How moist the soil is as it relates to the temperatures can produce a spectacular color array or one that's dull and flat. Ideally, if the preceding spring produced a good deal of rain and summer weather was "normal," neither too hot, nor too cold, not too wet, nor too dry, the best autumn colors are produced.
A summer drought will likely delay peak foliage. Too much summer rain can have a similar effect. In other words, if everything is not in optimum balance, the colors can be delayed and appear muted.
What Makes Leaves Fall?
In early autumn, in response to the shortening days and declining intensity of sunlight, trees begin the processes leading up to their baldness (no PC emails; I'm follicly challenged myself). 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. These clogged veins trap sugars in the leaf. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall.
As autumn begins to yield to winter, the colors fade and the stems binding leaf to tree begin to weaken. Before long, the leaves are literally hanging by threads--the tiny arteries that brought them water and glucose during the summer. Fall's winds, leaf pickers, wild animals, almost anything that brushes up against them snap them off the tree.
Fortunately, the colors remain after the leaves have dropped, but only for a day or so, so if you want to collect and press them, you should take them off the trees yourself, or if you see one you really like on the ground, you can collect that and press it, but do it quickly. Once they dry out, they get very fragile and break easily.
Eventually, all of the leaves are rendered brown by the presence of tannin; the same substance that gives tea leaves their brown color after they're harvested.
While summer is the busiest tourist season in some New England states, fall is the busiest in the region overall. There's nothing quite like this time of year, nor is there any end to the ways you can view the powerfully colored canopy. Bring your camera.