Why Trees Transform into Stoplights in Autumn

It's easy to fall in love with Fall. It's the prettiest month of the year. There are plenty of tropes built up around consumerist fads, like pumpkin-spiced flavored everything, Black Friday shopping, and artistic films about people Falling in love. Despite the incredibly creative endeavors that people produce this time of year, it doesn't come close to the natural beauty of a forest full of green, yellow, orange, and red leaves.

Autumn trees near a lake

Fall turns a forest into nature's canvas, but what is the paint? As vibrant as Fall colors are, the process of leaves changing is a bit more morbid than you might think. The natural color of leaves is green, principally because of the pigment chlorophyll. Chlorophyll is a molecule that helps plants turn sunshine into energy. However, once Fall rolls around, and the sun takes a vacation of sorts, many species of trees have evolved to shed their leaves. Why would trees choose to get rid of one of their primary sources of energy?

It's a choice of efficiency. Trees need to put energy into their leaves to keep them healthy, which means during the Winter when there isn't much sunlight for the leaves to harvest, the tree would be using more energy than the leaves could help create. Once this balance tips beyond efficiency, trees break down the chlorophyll in their leaves and absorb the pigment back into their bodies. Then the trees lose their leaves for the winter months before regrowing them for spring.

Tree with no leaves

The process of chlorophyll leaving the leaves is what sparks this magnificent color change. The green pigment saps out of the leaves heading back into the tree's main trunk and branches. This results in other natural pigments like carotenoids and anthocyanins coloring the leaves. Carotenoids are responsible for the yellow and orange hues that you see on trees and can be found in other common Autumnal foods like pumpkins and yellow squash. Anthocyanin is a pigment that can tint things shades of red to blue and everything in between. Anthocyanins are found in anything from berries and fruits to purple cauliflower. The fantastic range in color that you get in a single tree during autumn, and sometimes on a single leaf, is due to the tremendous combination of pigments showing up.

Purple, yellow, red and green leaves

While these festive colors technically signal the shedding of leaves which could be considered a sad and somber occurrence, it's really just a hibernation, since next spring, the trees will grow fresh, bright green new leaves, ready to soak up the sun.

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