Fall is officially here, which means the leaves will change from green to shades of red, yellow, and orange. Buy why exactly does this annual event take place?
It all boils down to photosynthesis.
Leaves change color as chlorophyll, the pigment that makes plants green, begins to break down in colder weather, according to the National Park Service.
"When the temperature drops and there is less daylight, the tree begins to conserve the energy it generated in the spring and summer months," the NPS explains. "As autumn progresses, a tree will send a substance to each leaf called an enzyme that is directed to take apart chlorophyll pigments."
Once the chlorophyll breaks down, the other pigments that weren't visible to the human eye before are now on full display.
Every tree has a different combination of pigments, which gives leaves their unique colors: Yellow leaves contain xanthophyll, orange leaves contain carotene, and red leaves contain anthocyanin.
Darker red leaves are the result of a chemical change, according to the Smithsonian Institution. The deeper color appears when sugars that get trapped in the leaves produce new pigments that weren't part of the leaf in the growing season.
Temperature and rainfall can also affect the brightness of the fall colors.
Areas with more rain and cooler temperatures will see more vibrant colors compared to warmer, dryer locations.
"When there is more rain, the colors pop even more," the NPS says. "When there is a cool fall, the red maple leaves appear brighter as well."
Once the chlorophyll has been broken down and the tree has absorbed the last of the nutrients, then, of course, the leaves fall.
Fall foliage first appears in the northern U.S., and slowly makes its way south throughout October and November.
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