Why do leaves change color in the fall? Why are leaves green? Why don't leaves turn all of the colors of the rainbow? In this episode of But Why, we're talking about fall leaves, and how trees go from green to fiery red, orange and yellow.
Foliage is a big deal in Vermont, so we turned to Mike Snyder, Commissioner of Vermont's Department of Forest, Parks and Recreation for the lowdown on how leaves change color.
He says leaves are green because they contain a chemical called chlorophyll, which allows them to make their own food. Chlorophyll appears green to our eyes because it's reflecting the green wave lengths of light.
Not all trees lose their leaves in the fall, but when the days start to get shorter in the fall, that's the signal for broad-leafed trees to get ready for winter. The tree stops making chlorophyll and the green color fades, unmasking colors that were there all along: the yellows and reds.
Meanwhile, another process is happening. The broad-leaf trees want to drop their leaves because those leaves can't withstand winter. So the leaf forms a boundary between itself and the twig, allowing the rain and wind to blow the leaf away.
The tree goes dormant for the winter. It slows down and lives on stored food. But it has already packed away buds for next spring.
When the new leaves emerge next spring, there is another brief period of red color when the buds break open.
Listen to the full episode for more.