How do trees communicate (without the Lorax, that is)?

I am the Lorax. I speak for the trees. I speak for the trees, for the trees have no tongues.

And I'm asking you sir, at the top of my lungs – that thing! That horrible thing that I see! What's that thing you've made out of my truffula tree?

Find yourself a patch of forest. Sit among the trees and if you're quiet (and a breeze is blowing) you'll hear whispering and moaning. Folktales and legends say it's the trees speaking to us. As Dr. Seuss's Lorax points out, trees can't really speak to us directly – at least not using words.

But even if they can't speak, trees can indeed communicate. Back in 1982 Ian Baldwin, currently director of the Max Planck Institute for Chemical Ecology, published a paper showing that young trees that were damaged as if attacked by hungry insects increased production of tannins and several other chemical compounds. Those chemicals were known to inhibit growth and foraging of insect larvae and so presumably helped defend the trees from further attack. They also discovered that undamaged trees in the same enclosure started producing similar compounds. Baldwin and his colleagues concluded that the damaged trees were releasing volatile compounds into the air. Those chemicals served to warn the undamaged trees of potential danger, and induced them to begin to mount their own defenses.

Since then, advanced molecular analysis and genetics have been used to study the so-called "talking tree" phenomenon in more detail. Plant leaves release a number of different chemicals, from simple small molecules like ethylene to more complex compounds like methyl jasmonate. These compounds diffuse through the air, and if they come in contact with the leaves of responsive plants, those plants respond with changes in chemical synthesis and growth.

Plant roots also secrete a number of different communicating chemicals. These compounds aren't able to travel as far through the soil as volatile compounds can drift through the air. Instead they locally fight of insect pests and battle nearby plants for growing room. Those chemical signals are also in the process of being deciphered, and that information is already being used to genetically engineer pest-fighting crops.

While the forms of chemical plant communication we currently are aware of are essentially non-directed shouts of "Danger!" or "Stay away!" rather than conversations, a recent public Q&A session with Ian Baldwin touched on some more speculative possibilities.

So what about fiction?

SF has a number of examples of tree-like aliens (such as Orson Scott Card's Pequeninos or the lonely female tree beings in Jack Skillingstead's "Rescue Mission") and fantasy creations like Tolkien's Ents, but I couldn't come up with any stories with scientifically plausible talking trees.

One big problem is intelligence – or more specifically the lack of it. To truly converse an entity must be able to think, and there is nothing that suggests that trees or other plants have any means of doing that. But once that hurdle is crossed (genetically engineered nervous systems, perhaps?), I think there's a plausible leap to be made from the current simple modes of Earthly plant communication to full-fledged chemical conversation.

I wonder what they'd say?

More technical information:

- Baldwin IT and Schultz JC "Rapid Changes in Tree Leaf Chemistry Induced by Damage: Evidence for Communication Between Plants Science 221(4607):277-279 (1983) DOI: 10.1126/science.221.4607.277

- Baldwin IT et al. "Volatile Signaling in Plant-Plant Interactions: "Talking Trees" in the Genomics Era" Science 311(5762):812-815 (2006) doi: 10.1126/science.1118446 (free pdf)

- Bais HP et al. "How plants communicate using the underground information superhighway" Trends in Plant Science 9:26-32 (2004) (free pdf)

- Science Special Online Collection: Plant Volatiles - From chemistry to Communication (2006)

- Live@AAAS Ian Baldwin on Talking Trees (Transcript)

Top image: Oak trees in October. Perhaps they are discussing the cooling weather? Photo by me.

This post originally appeared on Science In My Fiction.