Question: Why do leaves change colour in the fall?

Sam Geen answered on 20 Jun 2013:

Leaves are green because they’re full of chlorophyll – which is green because it’s sort of in the middle of the spectrum of light that the atmosphere lets through from the Sun, so it’s the best colour to trap the most light to make food for the plant. There are a bunch of other things in the leaves that are red/yellow/brown, like carotenoids, anthocyanins, and cell walls (and yes, I looked these up on Wikipedia). When autumn arrives, the plant stops replacing the chlorophyll so you see the colour of these things.

So why do plants lose their leaves in winter? Leaves are great for sucking in light and moisture when it’s summer, but in winter the tree goes into water-preserving mode, and leaves are bad at preserving water because they’re so big and wide, so the tree gets rid of them until spring. Some trees, like pine trees with needles instead of leaves, don’t have this problem and can keep them all year round.

Also, fall? Have some national pride and call it “autumn”! 😛 (just kidding)