What eastern Oklahoma’s changing leaves tell us about the weather

By Wayne Adams

Climate Scientist

Every autumn, the forests of eastern Oklahoma begin their annual transformation from summer green to shades of yellow, orange, red and brown. From Heavener and Poteau south toward Talihina and across the Ouachita Mountains, fall foliage can provide some of the most beautiful scenery in Oklahoma.

But those changing leaves can also tell us something about the weather and climate conditions the trees have experienced.

The primary trigger for fall color is the shortening of daylight as autumn progresses. Trees begin reducing chlorophyll, the pigment responsible for their green appearance. As the green fades, yellow and orange pigments become visible. Some species also develop the reds and purples associated with brilliant autumn foliage.

Weather determines much of what happens next.

Cool Nights Can Bring Better Color

Some of the best fall color occurs when eastern Oklahoma experiences sunny autumn days followed by cool, but not severely freezing, nights. Those conditions can encourage brilliant reds, oranges and yellows.

If autumn remains unusually warm, particularly at night, the progression toward peak color can be slower. Extended cloudy or rainy periods can also affect the intensity of the colors.

This means two autumns can look completely different even though the forests contain the same species of trees.

Drought Leaves Its Mark

Rainfall during spring and summer matters as well.

Trees experiencing adequate moisture generally enter autumn in better condition than trees that have endured prolonged drought and excessive heat. When drought becomes severe, leaves may curl, develop brown edges or begin falling prematurely.

This is important because early leaf change doesn’t automatically mean an early winter is coming.

A tree changing color unusually early may simply be stressed.

That distinction becomes especially interesting when observing forests rather than individual trees. If only one tree changes early, the cause could be something very local. If trees across a large portion of eastern Oklahoma begin showing similar changes at approximately the same time, broader weather conditions deserve consideration.

Eastern Oklahoma Provides a Natural Climate Laboratory

Eastern Oklahoma is especially useful for observing these changes because forests cover so much of the region.

Oak, hickory, sweetgum, maple, sumac and numerous other species respond somewhat differently to autumn conditions. Hickories frequently provide brilliant yellows and golds. Sumac can turn deep red. Sweetgum can display mixtures of yellow, orange, red and purple. Oaks often provide combinations of red, brown and yellow.

The mountains around Heavener, Talihina and southeastern Oklahoma also create differences in elevation, sunlight, temperature and soil moisture.

You can sometimes see autumn progressing across the landscape.

Leaves Remember the Growing Season

In a sense, every autumn leaf carries a record of the growing season that preceded it.

A tree has experienced months of heat, rainfall, dry periods, thunderstorms, humidity and changing soil moisture before October arrives. Those conditions influence the health of the tree and can affect how its leaves behave when autumn begins.

That makes fall foliage an interesting secondary climate indicator.

Leaves cannot tell us what the temperature will be next week, and they shouldn’t be treated as a replacement for weather instruments. But observing vegetation over many years can reveal changes in the timing of seasons.

Scientists refer to the study of recurring biological events—such as flowering, budding, migration and autumn leaf change—as phenology.

What I Will Be Watching This Fall

This year, I will be paying attention to four things across eastern Oklahoma: when widespread color begins, how quickly the transition occurs, how brilliant the colors become and how quickly the leaves fall afterward.

I will also be watching the difference between valleys, hillsides and higher elevations.

If leaves remain healthy and gradually progress from green into brilliant fall colors, that tells a different story than widespread browning and premature leaf drop following prolonged heat or dry conditions.

Recording those observations every autumn could eventually produce something even more useful—a local record showing approximately when eastern Oklahoma’s forests reached peak color each year.

After 10 or 20 years, changes in that timing could become interesting climate information of their own.

My Climate View

I don’t believe we should look at one tree turning red in September and conclude that our climate is changing. There are simply too many other factors involved.

But I do believe we should pay attention when nature repeatedly changes its schedule.

If peak foliage gradually begins occurring later, if leaves remain green deeper into autumn, or if increasingly hot and dry summers cause premature browning and leaf loss, those observations deserve to be recorded and compared with temperature and rainfall records.

Eastern Oklahoma’s forests therefore provide more than beautiful scenery.

They provide another way of observing the environment around us.

When you drive through Heavener, Wister, Poteau or the Ouachita Mountains this fall, look beyond the colors themselves. Notice when they appeared, where they appeared first and how long they lasted.

The trees have spent an entire year responding to their environment.

Autumn is when some of that story becomes visible.

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