Green leaves turn red, yellow, and orange in autumn. This seasonal change follows a clear scientific process based on plant chemistry and sunlight.
Leaves get their green color from a pigment called chlorophyll. Chlorophyll acts as a tiny solar panel. It captures sunlight and uses water and carbon dioxide to make food for the tree. This process is called photosynthesis. Trees make new chlorophyll all spring and summer while the weather stays warm and sunny.
As autumn arrives, days grow shorter and temperatures drop. Trees sense this seasonal shift. They prepare for winter dormancy. Trees stop making new chlorophyll and seal off the pathways between branches and leaves. Existing chlorophyll breaks down and fades away.
Without the dominant green chlorophyll, other pigments hidden inside the leaves finally become visible. Carotenoids produce bright yellow and orange colors. These pigments exist in the leaf all summer, but the strong green chlorophyll masks them. Anthocyanins create vivid reds and purples. Trees manufacture anthocyanins in autumn using trapped sugars and bright autumn sunlight.
Different tree species produce different color combinations. Maples turn brilliant red. Birches and aspens display bright yellow. Oaks show rich brown shades. Weather conditions also affect color intensity. Sunny days and cool nights produce the brightest reds.
After colors peak, leaves detach and fall to the ground. This protects trees from freezing damage and water loss during harsh winter months.
Why do trees seal off their leaves before winter?