Last spring, a legion of Boulder-based scientists descended on a walnut orchard in California for the kind of ho-hum experiments you’d expect from the National Center for Atmospheric Research: They wanted to learn how hydrocarbon compounds emitted by plants can affect air pollution and weather. What they got instead was a startling, Lord of the Rings-esque discovery. “It appears that plants have the ability to communicate through the atmosphere,” says Alex Guenther, an NCAR senior scientist. Based on previous work in sterile labs, researchers had suspected that plants could communicate, but the NCAR group verified it could happen in the “real world.” That’s right—trees can talk.

The revelation came thanks to a broken sprinkler system. The normally well-watered trees went thirsty for five days and started to panic. The artificial drought caused the stressed-out plants to produce methyl salicylate, an aspirinlike chemical. What’s more, the trees didn’t keep the drugs to themselves: They released the pain-relieving chemical into the air, serving as an ecosystem-wide alert to other plants. Researchers believe the warning can indicate stresses other than just drought, including insect infestation, disease, and extreme temperatures.

5280 January 2009
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The researchers think the arboreal aspirin is the equivalent of an animal’s immune system—the chemical helps provide resistance and recovery from disease. While this early-warning signal seems to be intended for other plants, Colorado farmers and forest managers could gather their own data from fields and forests and send samples to a lab. If results show high levels of the chemical, they could identify stressed trees before they show visual signs such as dead leaves. To learn more, NCAR recently launched a related study at the Manitou Experimental Forest near Colorado Springs. “Plants are talking,” Guenther says. “Now what we need to find out is whether the other plants are listening.”