Why do leaves turn red in fall?

Towards the end of summer and into autumn, the veins of a leaf used to transport liquid to and from the leaves begin to shut down and chlorophyll production decreases. This allows carotenoids and anthocyanins to show through as the colours we know as autumn colour. The green colour of leaves is due to the presence of chlorophyll; a dominant green pigment that masks other colour pigments found in leaves, such as the carotenoids which give us oranges and yellows, and the anthocyanins which give us reds and purples. Reasons for this process could be  that the red anthocyanins protect the leaves from harmful rays of the Sun during cold weather and at the same time act as a warning signal for insect pests to be avoided, while the tree sheds its leaves.

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