FLAGSTAFF, AZ (3TV/CBS 5) -- What did the leaf say to the tree at the beginning of autumn?
"Don't look at me, I'm changing!"
Get it? Corny jokes aside, fall foliage this time of the year can be so beautiful in the mountains of Arizona. Many from the Valley will flock to places like Flagstaff for a little leaf-peeping as aspens shine with leaves of gold, while maple trees flaunt deep shades of red.
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But what makes leaves change from green to these bright hues? To answer this question, we first have to understand what leaves do for the rest of the year.
Leaves are like energy factories for nature. Plants, like trees, suck up water from the earth through their roots. Then, they use carbon dioxide from the air and sunlight to create oxygen and glucose. This process is called photosynthesis, which means "putting together with light." A chemical called chlorophyll is what gives leaves their green color.
Plants will grow during the summer with long days of sunlight. As days become shorter, trees will begin to prep for winter. During the winter, there's not enough light for photosynthesis, so the green chlorophyll will disappear.
As the bright green fades away, we begin to see yellow and orange colors, which are the compounds known as Carotenoids and Anthocyanins. In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops and the glucose turns into a red color.
According to the U.S. National Arboretum, certain weather conditions at each stage of the leaf growing season work to the benefit or detriment of bright fall foliage.
During spring, a wet growing season is ideal.
From summer into early autumn, sunny days and cool nights are best. While adequate rain is good during the early growing season, it works to mute colors in the early fall. Cool temperatures and lots of sunshine cause chlorophyll to be destroyed quicker, allow yellows and oranges to be revealed sooner, and also promote the creation of more anthocyanins. While cool is best, too cold is detrimental. Freezing temperatures and frosts can kill leaves.
During autumn, calm days prolong viewing opportunities. Once autumn arrives, leaves need time for the buildup of chlorophyll to entirely fade and their dormant pigments to fully take over. Gusty winds and hard rains can cause leaves to fall before their full color potential is reached.
The conditions that make for spectacular autumn color displays are a rainy growing season, followed by a dry autumn with warm, sunny days and cool, but not freezing nights.