Where does one go to see some of the best fall foliage? How can one tell what to look for?
“Red maples turn a nice brilliant, full-red,” said UMO Alumnus Venice Bayrd, the head horticulture librarian for Longwood Gardens, the world-premier display garden in Pennsylvania. “If you want to cultivate a landscape, plant the ones known for the colors you want. If you’re thinking of where to look, think about where certain types of trees grow. For Maine, sugar maples are excellent. They’re so prevalent in the area, and have some of the most brilliant colors. Norway Maples are almost always yellow, if you’re hoping to see a lot of that color.”
But what makes a leaf change its color?
“Oh, that’s complicated,” Bayrd said. “That depends on so many factors. Beyond the amount of water and sunlight a plant gets, there’s a lot to do with pigments and sugar levels, and carbohydrates.”
Like people, leaves have pigments. And like a person’s skin, the color of a leaf is the product of chemical reactions between different pigments produced by the body, or, in this case, the plant.
Green leaves are green because of an abundance of chlorophyll. This compound is a porphyrin class pigment. It is the primary pigment in leaves. Chlorophyll production in a plant is caused by sunlight.
Sunlight is the key to the changing of leaf color. So a good question to ask when asking why leaves change color is, “What else changes in the fall?” The amount of sunlight changes in the fall. It decreases. Due to the decreasing amount of sunlight in the fall, a plants production of chlorophyll decreases, much like the upbeat mood of a person who lacks abundance of natural light. You could say the dulling and changing of a leaf’s color is something like seasonal defective disorder. Like our moods, a leaf’s common color changes because its metabolism changes due to a drop in its exposure to the sun.
The reduced production rate of a plant’s main pigment causes a ratio – or balance – of other pigment classes in a plant to shift. Chlorophyll breaks down at a constant rate, causing the leaf to fade gradually. During the breakdown, and once complete, the secondary pigments, cartenoids and flavonoids, become more apparent. The Cartenoids in leaves are lycopene and xanthophylls. The first compound is red, and the second is yellow. These two compounds, slowly becoming the majority in the leaf, take over the color control. Viola! The leaf fades to red or yellow.
The flavonoids are a little more complex, consisting of three different compound types. They are flavone, flavonol, and anthocyanin. The first two both appear yellow, but the third is a cornucopia of possibilities. Red, blue, purple, magenta – you name it.
A big part of anthocyanin’s complexity includes the presence of sugar in its molecular structure, and is thus dependent on the carbohydrates a plant contains – which is dependent on soil quality, water levels, and more. This phenomenon of color possibility is mainly attributed to the acidity level though.
The compound changes its color with the pH level. And finally, the amount of light affects the compound’s vividness. Like a glow-in-the-dark sticker collection, the more light, the much more bright.
“I like the beeches, the fagus species,” Bayrd said. “Those are relatives of the oak. They hold their leaves through most of the snowfall, and are nice because you can hear the rustle. It creates a nice effect. If you want to know more, go to your state Cooperative Extension Service.”
Maine’s Cooperative Extension Service is done through the University of Maine.
“They are a huge, rich government service, and it’s free to residents of the state,” Bayrd said.
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