Newswise — LEXINGTON, Ky., (Sept. 29, 2017) – Every year around this time, nature puts her greens to bed and awakens her autumn colors. That palette of reds, yellows and oranges painting the landscape is part of a very important ecological process.

Throughout the growing season, chlorophyll, the green pigment in leaves, photosynthesizes sunlight and carbon dioxide into sugars trees need to survive and thrive. As daylight hours shorten in late summer and early fall, a layer of cork cells forms at the base of each leaf. This restricts the flow of water and minerals into the leaf, which means spent chlorophyll cannot be replaced. As chlorophyll dies, it no longer masks other pigments present in the leaf —the yellows, oranges and browns of carotenoids.

The quality of light also affects color brilliance. The production of one group of leaf pigments, the anthocyanins, is dependent on the breakdown of sugars in the presence of the bright light in late summer.

Tree species have their own signature colors at this time of year. Oaks typically show their reds and browns. Shades of yellow show up in hickories, tulip poplars, aspens and gingkos. Maples have a stunning array of colors, depending on the variety. Sugar maples turn orange-yellow or orange-red, and red maple takes on a deep red hue. The sassafras tree shows a rainbow of deep orange, yellow, scarlet and purple on its mitten-shaped leaves. Some trees, though, can disappoint. The leaves of elms and pin oaks just turn brown and drop.

But even if a tree doesn’t display impressive fall color, it still contributes to the environment. Nothing is ever wasted in nature, so minerals taken into the leaves during the growing season are recycled after the leaves drop to the ground. When the leaves decompose, their nutrients again are available to be taken up by the area’s flora, and organic materials nourish the soil.

“Year in and year out, the cycle continues, whether the season brings brilliant leaves or faded browns. It’s nature’s way of making sure the circle of life continues. This year’s growth feeds next year’s plants and animals,” said Laurie Thomas, extension forester in the University of Kentucky Department of Forestry and Natural Resources, part of the College of Agriculture, Food and Environment.

It’s early yet. On the calendar, autumn has just begun. A few trees are starting to change, but the big display is still ahead in most areas of the country. Nationwide fall foliage predictions can be found at