The Yak says it's almost time for the fall fall. It may sound silly, but it makes sense. Fall is the name of the season. It's also what leaves on many trees and shrubs do in autumn.
First comes the color show. Maples, oaks, birches and other trees whose leaves have been green all summer will soon be turning red, yellow and orange.
The coloring process depends on two things that happen this time of year: The amount of sunlight declines, and nights get cooler.
Inside each leaf are substances called pigments that produce colors. The green pigment, chlorophyll (KLOR-oh-fill), is the main pigment we can see during spring and summer.
Plants use chlorophyll to capture the sun's energy and turn it into food. Because there's a lot of chlorophyll in the leaves in the summer, the other pigments are hidden, so the leaves appear to be green.
Plants make chlorophyll most efficiently when it's sunny. But by autumn, the amount of sunlight each day declines.
Without sunlight, chlorophyll begins to break down. That allows the yellow and orange pigments that were inside the leaves all along to show through. On sunny days, the leaves continue making sugar, which forms the red pigment. Trees in the full sun have the brightest red leaves.
Fallen leaves decompose, providing nutrients that nourish other plant life. Gardeners often pick up old leaves to put on their plants or compost piles to get the benefit of natural, free nutrients.
After the leaves fall, it's easier to see and appreciate the evergreens. Like their name says, they stay green all year.