Photo: Paul Bica (Flickr)

If you live along the U.S. Eastern Seaboard, there’s a good chance you’ve noticed a distinct lack of vibrant autumn foliage this year.

From North Carolina to Pennsylvania, lots of trees are still green, while others have gone from green to brown. Western Maryland’s normally-fiery fall foliage is being described as “disappointing” and “pretty drab,” while recent reports from Pennsylvania and Virginia suggest forests in these states are past due for a color change. A plant physiologist at Appalachian State University described western North Carolina’s foliage as “the strangest I’ve ever seen,” while the Foliage Network, which provides regular fall foliage reports across the country, summed up the dismal state of affairs in an October 25 update on the Mid-Atlantic and Southeast thusly: “Yeesh...This is truly a bizarre foliage season.”

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So what the hell’s going on?

The decline in light availability associated with winter is a primary cue for foliage to start changing color and trees to start dropping their leaves. But the weather also plays a role.

“The pump for fall colors is the cool nights and warm days,” Anne Hairston-Strang, a forest hydrologist at Maryland’s Department of Natural Resources Forest Service told Earther.

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Cool temperatures and longer nights signal to trees that it’s time to stop producing green chlorophyll. As this photosynthetic pigment degrades, yellow and orange carotenoids present throughout the growing season are unmasked. For some trees, autumn’s changing light conditions also trigger the production red, pink, and purple anthocyanins.

Hairston-Strang noted that the start of fall in Maryland was abnormally warm, which likely delayed the onset of color production. Summer into September was also very wet, which Hairston-Strang said can further delay fall colors and result in a less vibrant show.

These conditions weren’t limited to Maryland. Across the Mid-Atlantic and into southern New England it was unusually warm and wet this summer, with conditions remaining swamp-like well into September. Michelle Stoll, a public information officer at the Virginia Department of Forestry, said her state’s leaves were “definitely behind” and pointed to the recent raininess as a likely culprit.

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There are other factors that might be contributing to garbage autumn in some locales. Frost damage can cause leaves to go right from green to brown. Drought during the growing season can also stress trees out, causing their leaves to drop without a color show, according to Kevin Smith, a plant physiologist with the U.S. Department of Agriculture’s Forest Service. Foliage diseases, which often infect trees in late spring or early summer—and are also associated with very wet weather—can have a similar effect.

“People know fall foliage being part of senescence or aging, and it is that,” Smith told Earther. “But it’s healthy aging.”

As for the effects of climate change? The frost-free season has been gradually lengthening across the Northeast, a trend that’s expected to continue and could lead to more delayed seasons like this year. In New England, a combination of warmer and wetter winters is expected to threaten iconic color-producing trees like sugar maple, according to a recent government report. Smith noted there could be myriad potential effects, from changes in species composition to changes in the genetic makeup of the species present, but was reluctant to predict how that might impact future fall foliage displays.

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The good news for leaf peepers this year? The foliage in upstate New York and New England, while somewhat delayed due to the warmth, seems to have eventually made a vibrant showing.

“I have been following color in New Hampshire and Maine, and this has been a great year,” Smith said. “It’s been pretty much on the money.”