Why leaves change color (and why so late now)
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The autumn leaves could show up late this year — and with softer shades.
Why it matters: Fall foliage isn't just pretty scenery or a tourism draw — its timing and vibrancy could flag deeper forest health concerns linked to climate change.
What's happening: There seems to be two separate things at play, University of Vermont professor of forest science William Keeton tells Axios.
1. Weather extremes, like drought and excessive rainfall, can "stress" trees, which cause them "to brown up and drop their leaves," Keeton says.
- "So by the time we get to the great reveal, there's less color, and maybe the overall intensity is dampened," he says.
2. Warm nighttime temps late into fall mean trees miss the memo about changing seasons.
- They only get the signal to shut down and prepare for winter when evenings get cool. If that happens late, then the onset of foliage occurs late — almost two weeks later, one study found.
How it works: When nights cool, trees pull nutrients and energy from their leaves and the green pigment fades. That reveals other pigments — including the same ones that color carrots and apples — turning leaves yellow, orange and red.
- The intrigue: The deep red and purple color in other fall leaves come from a group of compounds called anthocyanidins, which aren't completely understood.
What we're watching: Scientists are still piecing together how climate extremes shape fall foliage, and what that means for the long-term health of forests.
Go deeper: When and where to see peak fall foliage
