Why some leaves change colour before falling
As many deciduous trees prepare to shed leaves, green chlorophyll breaks down and is no longer replaced at the same rate. Yellow and orange pigments already present become easier to see. Some species also produce red pigments, so autumn colour reflects several chemical changes rather than green simply turning red.
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The green layer no longer dominates
Chlorophyll strongly influences the green appearance of a healthy leaf. Other pigments, including yellow and orange carotenoids, are also present but can be masked by that green.
During seasonal leaf ageing, chlorophyll breaks down. The tree can recover some nutrients before the leaf is shed, while the changing pigment balance alters its colour.
Red colour often has a different origin from exposed yellow pigments. Many species produce anthocyanins during autumn, adding red or purple tones.
- Chlorophyll loss makes existing pigments more visible.
- Newly produced pigments can add other colours.
- Species and weather influence the final display.
Not every tree follows the same pattern. Some leaves turn mostly yellow, some become red, and others brown with little colourful transition before they fall.