While you were playing in the hot sun during summer vacation the trees on the streets, in the parks, and in the forests were working hard to keep you cool. To feed the shiny green leaves that make shade, trees use sunlight to convert water and carbon dioxide into sugar. This is called photosynthesis.
Now it's autumn, and you're ready -- okay, almost ready -- to be back in school. Those hardworking trees, on the other hand, need to take a break from all that photosynthesizing. When leaves change color from green to yellow, bright orange, or red, you'll know that trees are beginning their long winters rest.