Question: why do leaves change color in the fall

Duncan McNicholl answered on 6 Nov 2017:

Because they’re closing up shop.

Leaves fall off the trees for winter because having leaves means using up some energy to keep them green, and losing a bit of water from them the whole time (if you’re ever stuck in the wild and need some water, you can fasten a plastic bag over a leaf and it will slowly fill up with fresh drinkable water). The energy and the water are ok to use as long as the tree is getting something back, like energy from sunlight, but in the winter there’s less sun and so most trees decide it’s not worth it and block off the leaves and let them die and fall off.

When you take all the chemicals that make leaves green and let them decay naturally without energy or water, they turn orange and red and brown, and the leaf dries up and falls off the tree.