Slate's Explainer: How Aspens Turn Color in the Fall

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ALEX CHADWICK, host:

OK. One more intriguing footnote to this story: a note that Lewis Libby sent to Judith Miller upon her release from prison. Quote, "You went into jail in the summer," he wrote. "It is fall now. Out West where you vacation, the aspens will already be turning. They turn in clusters because their roots connect them. Come back to work and life," end of quote.

Some have taken that as an attempt to send Judy Miller a message, although exactly what that message is who knows. The letter piqued the interest of the Explainer team at the online magazine Slate. Here is Slate's Andy Bowers to answer the question: Do the leaves of aspen trees really turn in clusters because their roots connect them?

ANDY BOWERS reporting:

No, they don't. Aspen trees do grow in clusters, or clones, that share a common root system, and they do have identical DNA. That doesn't mean, however, that they all turn--that is, change colors--at the same time. Leaves turn colors in the fall according to both genetic and environmental factors. The exact day depends on the sunlight, temperature and precipitation to which they've been exposed. Aspen clusters can be huge, with the largest recorded spread out over 17 acres. So certain trees could get more sunlight than others and change color on different schedules. A week or more might elapse between the turning of the first and last trees in a stand of aspen.

However, shared genes do mean that when clusters of aspens turn in the fall, they all turn the same color. The leaves on every tree in one clone may turn gold while those on trees in another clone turn crimson.

CHADWICK: Thank you, Andy Bowers, Slate senior editor. That Explainer was compiled by Daniel Engber.

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