Clemson scientist says ‘Get out and explore’ fall color changes

As fall arrives, Mother Nature spreads her canvas across the southern Appalachian Mountains, preparing to paint tree leaves in vibrant hues of reds, purples, golds and browns.

These colors will cover the green leaves that adorn trees in spring and summer, creating a masterpiece that has excited people for years. Known as the fall color season, this event is like pumpkin spice coffee for those who eagerly await its arrival. In just a few weeks, leaf-seekers can experience it in full effect.

Sitting at an elevation of 6,684 feet, the Blue Ridge Parkway in North Carolina is a popular spot for enjoying this seasonal treat. Leaves in the area have started changing colors.

“We’re starting to see some leaf color change in the higher elevations,” said Don Hagan, associate professor of forest ecology at Clemson University. “The coming weeks will be a good time for people to get out and explore and see what’s happening with leaf colors at different elevations.”

Just 60 miles away from the Parkway, Clemson, South Carolina, sits at an elevation of 769 feet. Some leaf color changes are occurring in Clemson, but not as much as on the Parkway. Elevation contributes to leaf color change.

“The way elevation influences fall color is the timing,” Hagan said. “At higher elevations, it’s cooler, and fall weather comes a little earlier. So, the leaves start changing color earlier. The cooler climate also allows different species to grow at higher elevations. Some of these species are more typical of the northeastern United States, or even Canada.”

Leaf color changes are expected to peak in early-to-mid October in North Carolina and in early November in South Carolina.

The Blue Ridge Parkway is home to about 140 species of trees, including tall conifers, which are evergreens and stay green year-round. Conifers, such as hemlocks, spruces and firs, bear needles and produce cones.

Other trees are deciduous species, including northern red oaks, maples, yellow-poplars, and more. Leaves on deciduous trees start changing colors during the fall – or in some cases, late-summer.

The science behind fall leaf color changes

Hagan and other scientists have long studied the changes that occur in trees during the fall. While the exact mechanisms are not fully understood, they have a basic explanation.

“Three main factors that influence autumn leaf color are leaf pigments, length of night and weather,” Hagan said. “As the days grow shorter and nights become longer and cooler, chlorophyll stored in the leaves breaks down, revealing the orange and yellow pigments that were masked during the warmer months.”

Pigments are chemical substances responsible for leaf color. Chlorophyll is the green pigment seen during spring and summer.

Chlorophyll uses sunlight to produce sugars that serve as food for plants. Trees store these sugars for use during the dormant winter period. During the growing season, chlorophyll is continually produced and repaired, causing the leaves to appear green.

In fall, as days shorten and nights lengthen, chlorophyll production slows. Eventually, production stops entirely, and chlorophyll degrades. The carotenoid and xanthophyll pigments present in the leaves are unmasked, showing their colors. Carotenoids produce orange tones while xanthophylls produce the yellows.

Weather conditions also play a role in the amount and brilliance of leaf colors. Temperature, sunlight and moisture are the main influencers.

“Ideal conditions for fall color are clear and sunny with a progression of mild cold fronts that gradually lower temperatures without causing an early frost,” Hagan said. “We don’t want extended periods of gray, soggy, cloudy weather. And we definitely don’t want strong winds, as this can cause leaves to fall off before they fully change color. Excessively dry conditions can also cause some species to change color and drop their leaves early. We’ve seen that in some places this year, but it is not widespread.”

Sunlight triggers the chemical reaction that brings out the brightest colors, especially the most vibrant reds and purples.

In some species, sugars produced by leaves interact with bright sunlight in a chemical reaction that spurs the production of anthocyanins, which tint the leaves in reds, purples, and crimsons.

Eventually, the leaves become useless, and trees stop investing energy in them.

“One of the first things that happens when a tree stops investing in a leaf is the chlorophyll degrades,” Hagan said. “The leaf stops rebuilding chlorophyll, and the other pigments become visible.”

Soon the leaves die and fall to the ground where they decompose and restock the soil with nutrients.

For people eager to see the changing colors, Hagan encourages them to get outside.

“Go for a drive and look for the changing leaf colors,” he said. “Some places will have more vibrant colors than others, so get out and explore.”