When are fall leaves on Charlotte trees expected to appear? Look for these signs.

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Fall is officially here and it won’t be long before leaves transform into vibrant shades of red, orange and yellow.

Some areas of the North Carolina mountains along the Tennessee border have already started to see “minimal” change in colors, but a more widespread transition is expected in late September for the western part of the state, according to the foliage prediction map SmokyMountains.

The Charlotte area isn’t expected to reach peak color change until late October, according to the map.

But if the leaves start to change earlier or later than expected, it could spell trouble for the trees.

Why do leaves change color in the fall?

Leaves are green during the spring and the summer because they are making chlorophyll, which helps them produce energy from sunlight, according to the National Oceanic and Atmospheric Administration. This process is known as photosynthesis.

During fall, when the days get shorter, leaves stop making chlorophyll. Once that happens, the green color starts to fade, and red, orange and yellow colors begin to appear, according to the NOAA.

RELATED: When could leaves change colors in NC mountains? This fall foliage map has clues

Why do leaves change color earlier than expected?

Early fall color could indicate that a tree is under stress, Bob Bricault wrote for the Michigan State University Extension.

Damage to the base of a trunk caused by lawn mowers or animal feeding can reduce the flow of water and nutrients to a tree, leaving it susceptible to other problems, according to Bricault, adding that these trees often change color early.

Drought-stressed trees can also change color before fall starts, but the impact of extreme heat can be reduced by watering and proper use of mulch to reduce water loss from the soil, Bricault wrote.

Why do leaves change color later than expected?

Color change can be delayed if temperatures stay warm throughout fall, Leanne Potts told Better Homes & Gardens.

Heather Alexander, an associate professor of forest ecology at Auburn University, said late color change is one of the effects of climate change.

“Changing temperature is something that we’re seeing, obviously, and it’s getting warmer on average across the globe,” Alexander told Better Homes & Gardens. “The trees are sensing this.”

Each 1.8-degree increase in temperature can delay color changes by three days, Alexander said, adding that extended droughts can cause leaves to fall off trees before they change.

Excessive rainfall from storms can also hinder color change. If a storm knocks too many leaves off a tree, the remaining leaves have to work harder to make chlorophyll for it, meaning they will stay green longer, Potts said.