Throughout spring and summer, chlorophyll, the green pigment leaves use to absorb sunlight for photosynthesis, dominates leaf color so thoroughly that it masks other pigments already present in the leaf.
As daylight hours shorten and temperatures cool in autumn, deciduous trees respond by breaking down and reabsorbing chlorophyll from their leaves, which unmasks pigments that were there all along but hidden behind the green.
Chlorophyll Breaks Down First
What Determines Vivid vs. Dull Color Displays
Two main pigment groups become visible: carotenoids, which produce yellow and orange tones and are present in the leaf year-round, and anthocyanins, which produce red and purple tones and, in many species, are actually produced fresh in autumn in response to bright light and cool nights rather than simply being unmasked.
How vivid or dull a given autumn turns out depends heavily on weather. According to forestry researchers, a combination of warm, sunny days and cool but not freezing nights tends to produce the most vivid red displays, while an early hard frost, prolonged drought, or unusually warm nights can dull the overall color show, meaning the intensity of color varies noticeably from year to year even in the same location.
Sources
FAQ
Why don't evergreen trees change color like deciduous trees?
Evergreen needles have a different biology, including a waxy coating and a longer individual lifespan, and they shed and replace needles gradually rather than all at once each autumn.
What makes leaves turn red instead of yellow?
Red and purple tones come from anthocyanin pigments, which many species produce freshly in autumn, while yellow and orange come from carotenoids already present in the leaf year-round.
Does weather affect how vivid autumn colors are?
Yes, a mix of sunny days and cool nights tends to produce the most vivid displays, while early frost or drought can dull them.
About the Author
We reference USDA Forest Service, NASA Earth Observatory to explain the background and current understanding of this topic.
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