Why do the trees change color in the fall?

It seems a fairly obvious question for this time of year. My daughter asked me this question last week, and I was embarrassed that I didn't know what to tell her.

According to News@nature.com, color change in leaves is not very well understood. The predominant theory is that leaves change their color in order to recycle the last bit of nutrients from their leaves before they are lost. Thus, trees grown in areas with less soil nutrients will produce more brilliant leaf colors.

As the weather turns colder, the trees switch to winter hibernation mode. The green chlorophyll in the leaves breaks down and disappears, revealing the yellow carotinoids that have been lurking among the chlorophyll all summer. The brilliant red color that people admire comes from a pigment called anthocyanin, which trees produce in autumn. Why trees expend their precious energy producing anthocyanin is still a matter of study and debate. It is believed that anthocyanin acts as a sunscreen, protecting leaves which are more vulnerable to sun damage after the chlorophyll is gone. The protected leaves can stay on the trees longer, allowing leaf nutrients to be absorbed into the other parts of the tree. link