As the warm days of summer transition into the crisp air of fall, Pennsylvania’s forests undergo a spectacular transformation. The once-green canopy bursts into a kaleidoscope of reds, oranges, and yellows—a natural display unique to the state’s rich variety of native tree species.
Rather than being a mere visual spectacle, this transformation is a scientific process as trees prepare for the chilly months ahead.
“The driving force behind all of this is the plants are getting ready for winter, days are getting shorter … they don’t want their leaves to freeze. So they’re going to shut down. In that shutting down process, we’re getting I’d say, an explosion of colors, right?” explained Vince Cotrone, Penn State Extension Educator and Regional Urban Forester.
With over 130 native tree species, Pennsylvania offers a diverse range of hues and timings for leaf color changes, making it a top destination for autumn leaf peeping. “We have such a diverse forest,” said Julian Maza, service forester for the Pinchot Forest District. “There’s over 130 different species across the state, and again, each one of those, they have their own slightly different kind of color variations, different hues. They’re going to change colors at different times of the year.”
Changing Colors
Leaves are green due to chlorophyll, which is vital for photosynthesis. However, as days shorten, chlorophyll production ceases, allowing other pigments to emerge. This change results in the vivid hues of yellow from carotenoids and red or purple from anthocyanins.
The timing of peak foliage is consistent annually, influenced mainly by day length, according to Maza. Weather conditions, such as wet springs or droughts, can impact the vibrancy of the colors and the duration of the peak.
“What’s going to affect the fall colors and how vibrant they are, or how long the peak lasts, is really weather-dependent,” Maza noted.
Optimal Viewing
To experience the best of fall’s palette, timing is crucial. Cotrone suggests a trip to Susquehanna County or Pennsylvania’s Northern Tier in early October for prime viewing. The state’s varied tree species contribute to the timing and intensity of the color change.
For instance, northern hardwood forests, such as sugar maples and birches, change color sooner than oak and hickory trees found further south. Maza explained that soil types, remnants from the glacial era, influence tree distribution across regions.
Weather and Foliage
While the trees are in good health this year, Cotrone emphasized the importance of continued dry, sunny days and cool nights for optimal foliage. However, severe weather, like strong winds and rain, could cut the season short.
“If you’re starting to get fall colors and then all of a sudden you get wind and rain — man, what could have been a nice show for a week-and-a-half turns into a two-day show,” Cotrone remarked.
The Economic Impact
Autumn’s allure plays a significant role in Pennsylvania’s tourism, contributing $83.9 billion to the economy and supporting over 514,000 jobs in 2024, according to the Pennsylvania Tourism Office. The state welcomed 201.6 million visitors that year.
To aid visitors, the DCNR will publish weekly fall foliage reports starting October 1, detailing regional changes and providing viewing tips. The Pocono Mountains Visitors Bureau will also provide updates through October.
Maza pointed out that many state forests are popular for scenic drives, while Cotrone highlighted community festivals celebrating the season’s beauty. He suggests that local exploration might be just as rewarding as traveling far: “You don’t need to spend gobs of money on gas this year going to Boston or Vermont,” he said. “Stay in Pennsylvania, spend your money in Pennsylvania.”
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