The leaves changing color in the fall is not just for show; there’s real science behind it.
The role of chlorophyll
Leaves are green in spring and summer because of a pigment called chlorophyll. Chlorophyll is crucial for photosynthesis, the process by which plants use sunlight, water, and carbon dioxide to create food (glucose). It also gives leaves their bright green color.
What changes in the fall?
As fall arrives, the days get shorter and cooler, and sunlight becomes less intense. Trees respond by slowing down food production and eventually stop making chlorophyll altogether. As the green fades away, other pigments that were hidden under the chlorophyll start to become visible.
Where the colors come from
Carotenoids: These pigments produce yellow and orange shades and are always present in the leaf but masked by chlorophyll during the summer.
Anthocyanins: These are created in the fall and give leaves their red and purple hues. Interestingly, not all trees produce anthocyanins—so not all leaves turn red.
Tannins: These give some leaves, especially oaks, their brown color.
The exact colors you see depend on the type of tree, the weather, and how much of each pigment is present.
Why leaves fall
In addition to changing color, leaves eventually fall off the tree. This helps the tree conserve energy and water during the cold winter months, when it can't support its full canopy. It's part of a survival strategy that allows the tree to go into a kind of dormancy until spring returns.
The science is in the weather
The most vivid fall colors occur when there’s a combination of sunny days, cool nights, and just the right amount of moisture. Too much rain or an early frost can dull the display, while the perfect weather can make the trees look like they’re glowing.
