Leaves change color in the fall for the same reason you bring
in your patio cushions – to prepare for winter. All summer long, trees are busy at work
converting sunlight into the chemical energy they need to thrive. You know that process as photosynthesis. Eventually trees will need a rest from all
that light-converting work. And besides,
tender green leaves couldn’t handle damaging frost and freezing
temperatures. Winter dormancy is the
time for trees to rest up and rely on stored energy, but first they must
prepare defenses against the cold and freezing weather ahead.
Leaves contain several color pigments all summer, but the green
chlorophyll pigment hogs the spotlight because it is the main star in
photosynthesis. Therefore it masks the
other colors, or pigments, while the tree is in its energy production process. You can only see the green. Shorter days of sunlight and cooler nights cue
the trees to switch gears and begin preparation for winter. This means it is time to shut down the photosynthesis
process, so the
need for green chlorophyll decreases. As production of the green chlorophyll pigment grinds to a halt, it finally allows the red and yellow pigments that were there all along to outshine the green. Carotenoid pigments (think carrot) are responsible for the orange and yellow leaf colors that take center stage after chlorophyll pigments step aside. They are joined by anthocyanins pigments, responsible for the red and purple leaf colors you see. (They also give the red to apples.) After the brilliant color change process is complete and the background pigments have stolen the show, a final chemical reaction produces cells to seal off the connection between the leaf stem and the tree, like a scab, which then forces the leaf to fall off. Finally, energy production is put on hold and the tree can rest safely in dormancy. But come spring, sunlight and temperature changes will signal the tree that it is time to awaken and ramp up the food and energy production once again for another green, shady summer.
need for green chlorophyll decreases. As production of the green chlorophyll pigment grinds to a halt, it finally allows the red and yellow pigments that were there all along to outshine the green. Carotenoid pigments (think carrot) are responsible for the orange and yellow leaf colors that take center stage after chlorophyll pigments step aside. They are joined by anthocyanins pigments, responsible for the red and purple leaf colors you see. (They also give the red to apples.) After the brilliant color change process is complete and the background pigments have stolen the show, a final chemical reaction produces cells to seal off the connection between the leaf stem and the tree, like a scab, which then forces the leaf to fall off. Finally, energy production is put on hold and the tree can rest safely in dormancy. But come spring, sunlight and temperature changes will signal the tree that it is time to awaken and ramp up the food and energy production once again for another green, shady summer.
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