Question: Why do leaves change color in autumn?

Ian Cade answered on 11 Nov 2014:

As far as I remember being told… its that the leaves are always red and yellow, its just that most of the time this is masked by the more intense green colour of the chlorophylls that are used by the plant to harvest sunlight to make sugars.

So, why the change? In Autumn some trees loose their leaves. Rather than waste the resources used to make leaves each year, they extract as much goodness out of the leaves before they are discarded and this happens to include the chlorophyll.

Why do some trees loose their leaves, changing colour in the process? A variety of reasons:

-In the temperate zones there is less sunlight in the Winter, so not having leaves during Winter is not much of a problem.

-During the year the leaves are out in the sun continuously getting damaged (much like sunburn I expect) so they do need to be replaced from time to time.

but why all in one go?

-Parasites/fungi/insects build up on leaves during the year and if all the leaves are discarded at once so that there is nowhere for them to go, the plant is able to get rid of them and start fresh next year.

-In temperate zones, Autumn and Winter tend to have more rain and storms which could damage plants, knocking branches off and uprooting trees. So, rather like a ship furling its sails before a storm, some trees loose their leaves to reduce the amount of surface area the wind can pull on.

And there may very well be other reasons beyond these.