Q: Why do leaves change color in the fall before they fall off the trees?
A: As autumn drags on, leaves’ shades of green give way to hues of yellow, orange, red and brown before falling to the ground because less sunlight from shorter days produces chemical changes in the leaves.
Decreased sunlight means less green-producing chlorophyll production, allowing the chemicals that produce the fall colors to take over, according to the Wisconsin Department of Natural Resources.
Carotenoid produces yellow, orange and browns in trees, while anthocyanin produces red in some, but not all, trees.
You can find red leaves on oak, dogwood and maple trees, according to the DNR.
While shortening daylight hours trigger color-changing chemical reactions in the leaves, weather conditions also play a role in how vivid fall colors are, the timing and for how long they last, according to the DNR.
Although the orange, yellow and gold hues are generally constant from year-to-year, warm, sunny autumn days, ideally without nights that produce frost, make for the most vivid red-colored leaves, according to the DNR.
Warm, wet springs, followed by a summer that’s not too hot or wet, and a fall with plenty of warm, sunny days with cool, frost-free nights set up the best autumn colors, according to the DNR.
— Chris Aadland