Leaves change color in the fall mainly because the pigments in tree leaves are revealing themselves as daylight shortens and temperatures cool. Here’s a concise breakdown of the key processes:
- Chlorophyll breaks down: Chlorophyll gives leaves their green color and drives the photosynthesis that fuels the tree. As days shorten and temperatures drop, chlorophyll production slows and the existing chlorophyll degrades. As the green fades, other pigments that were always present become visible. This reveals yellow and orange tones from carotenoids, which are always there in the leaf but masked by the dominant green pigment.
- Carotenoids appear: Carotenoids (including carotenes and xanthophylls) are responsible for yellow, orange, and brown hues. They are more stable than chlorophyll, so once chlorophyll breaks down, carotenoids show through, contributing yellows and oranges.
- Anthocyanins can form: In many species, red and purple colors arise from anthocyanins, which are produced in the fall from sugars trapped in the leaf. The production of anthocyanins is influenced by light exposure, temperature, and the amount of sugars in the leaf. Reds and purples often appear in maples, dogwoods, and some oaks.
- Weather and day length matter: The timing and intensity of color change depend on factors like the length of daylight, daytime temperatures, nighttime temperatures, and the presence of sunny versus cloudy days. Bright sunlight can intensify red colors, while warm days and cool nights tend to enhance the overall color display. Wind and rain can cause leaves to fall earlier, influencing how vivid the colors appear on the landscape.
- Species differences: Different tree species produce different color palettes. Some may show mostly yellows and golds, others vivid reds, and some browns, depending on the balance of pigments present and how they break down during autumn.
If you’d like, I can tailor this to a specific tree species you’re curious about or connect the explanation to a local fall color forecast for your area.
