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This view from Heintooga Ridge Road offers a good vantage point to absorb the brilliant fall colors breaking out across the mountains in North Carolina in Great Smoky Mountains National Park. Research indicates the reliable fall color regime in the Southern Appalachians is affected by climate change.  Courtesy National Park Service

It’s just the latest way humans have altered Appalachian forests

This story originally appeared in the Conversation. Marc Abrams is a professor of forest ecology and physiology at Penn State.

Fall foliage season is a calendar highlight in states from Maine south to Georgia and west to the Rocky Mountains. It’s especially important in the Northeast, where fall colors attract an estimated US$8 billion in tourism revenues to New England every year.

As a forestry scientist, I’m often asked how climate change is affecting fall foliage displays. What’s clearest so far is that color changes are occurring later in the season. And the persistence of very warm, wet weather in 2021 is reducing color displays in the Northeast and mid-Atlantic. But climate change isn’t the only factor at work, and in some areas, human decisions about forest management are the biggest influences.

Longer growing seasons

Climate change is clearly making the Northeast warmer and wetter. Since 1980, average temperatures in the Northeast have increased by 0.66 degrees Fahrenheit (0.37 Celsius), and average annual precipitation has increased by 3.4 inches (8.6 centimeters) — about 8 percent. This increase in precipitation fuels tree growth and tends to offset stress on the trees from rising temperatures. In the West, which is becoming both warmer and drier, climate change is having greater physiological effects on trees.

My research in tree physiology and dendrochronology — dating and interpreting past events based on trees’ growth rings — shows that in general, trees in the eastern U.S. have fared quite well in a changing climate. That’s not surprising given the subtle variations in climate across much of the eastern U.S. Temperature often limits trees’ growth in cool and cold regions, so the trees usually benefit from slight warming

In addition, carbon dioxide — the dominant greenhouse gas warming Earth’s climate — is also the molecule that fuels photosynthesis in plants. As carbon dioxide concentrations in the atmosphere increase, plants carry out more photosynthesis and grow more.