Plants with brains: a mind-growing concept

  • Snag trees, defined as standing dead or dying trees, provide habitat for many mammals, amphibians and birds, including barred owls shown here. In Canada they'recalled “wildlife trees," and some timber harvests leave a certain number, honoring their natural resource value. Photo by Susan Clark—

Thursday, March 09, 2017

I've been thinking about trees lately, curious how sap rises against gravity; curious why sugar maples and a few other species deliver sap but oaks and most others don't. It's complex. Different trees have come up with different solutions to what challenges all plants and animals: finding food and safety.

I came on an article by Michael Pollan, wonderful Michael Pollan, in the New Yorker titled "The Intelligent Plant." Applying the concept of intelligence to plants rankles many. For intelligence, there has to be a brain.

Pollan is on the side of those who suggest that plants are too intelligent to have a brain. Where exactly would it be located? Whack up to 90% of a plant and it can recover and survive. Darwin suggested the roots were command central, and he used the word "brain." There's a great word for plants, "sessile," which means unable to move around.

There's an appealing spring wildlflower, the sessile bellwort, also known as wild oats.

After reading Pollan, I now know what sessile means. Plants are sessile, rooted in place.

Flight is not an option, so to survive they have to be acutely tuned in to what's going on around them: soils, moisture, light, gravity, nutrients, threats from herbivores, pollution, other plants. That's a lot of sensory processing, and it suggests a certain plant neurobiology. Plant "neurobiology" and "intelligence" are equally toxic concepts to many scientists and they are deal breakers for getting grant money. But minds are opening as more is learned about plants (despite not much grant money and no Nobel prizes).

Being sessile, plants need sophisticated means of finding food and detecting—and repelling—threats. An insect or deer munching a plant triggers defense chemicals that make the plant unpalatable, different chemicals for different munchers.

There’s evidence that plant neighbors of the same species pick up the threat signals. For some, hearing the munching triggers a defense.

There’s more. Corn is among plants that emit a distress signal when attacked by caterpillars that attracts certain wasps that parasitize the caterpillars.

We’re more familiar with the chemical signals (scents) flowering plants use to recruit beneficial pollinators. Plants produce nectar as a reward, and shut the supply off as soon as they’re pollinated.

Roots grow towards nutrients, veering away from other roots but not from inanimate objects (rocks); bean tendrils reach towards the nearest support rather than waving around randomly.

I’ve written here before about the cobwebby underground network of fungi that attach to tree roots. The threadlike network delivers moisture and nutrients to a tree community, impressively so, and in return takes sugars produced by the trees through photosynthesis, a skill underground fungi obviously lack.

Forest health—against stressors like drought, pollutants, pathogens—depends on this network.

Beyond exchanging nutrients, plant to fungi, “mother trees” in a forest community share nutrients with young trees until they can reach a certain height and light. There also is evidence of sharing with other species in experiments with white birch and Douglas fir. One produces an excess of carbon and nutrients at a time in the growing season when the other is in need, and vice versa. Communicating needs through the underground network, they share nutrients through it, too.

Does a forest community compete for resources or cooperate? Darwin has conditioned us to see everything as competition, survival of the fittest, but cooperation creates greater community resilience against shared threats: pollutants in soil, air or water; fire; ice storms and hurricanes.


What can we learn from the community of plants? Not much if we see them as separate automatons.

Michael Pollan mentions our fascination with artificial intelligence. He’s is on the side of learning from plant intelligence. We need plants more than plants need us. What can we learn from this network that could increase forest health as air, soil and water become more contaminated? How can we encourage plants’ natural defenses instead of over-relying on pesticides. Plants produce drugs like aspirin and beneficial opiates.

What’s to be learned there? Roots, given a choice between reaching towards a plant’s equivalent of a donut or a broccoli omelet, know to go in the direction of health for the organism.

Why don’t humans make healthy choices, both for the individual and the community? How have we departed from that wisdom? These are important questions.

Backyard Birder by Francie Von mertens appears every other week in the Monadnock Ledger-Transcript.