2019-02-09 / Outdoors


Do trees talk? you may be surprised

A decade ago, I read that trees communicate. When fed upon by forest pests such as caterpillars, trees produce higher levels of tannins to make their foliage less palatable to the insects.

And when a tree is under attack by foliage-eating insects, neighboring trees also respond to the attack by increasing their tannin levels -- even though no insects have yet fed upon their foliage.

Researchers have revealed that somehow through a pathway of chemical signals, trees can communicate to their neighbors to get ready, the caterpillars were coming.

Professor Suzanne Simard from the University of British Columbia has made some remarkable discoveries in the field of forest ecology. By studying radioactive tagged carbon molecules, she has found that in a forest trees cooperate and help each other by sharing nutrients.

In the Pacific Northwest, douglas fir and paper birch trees help each other. Paper birch trees shared carbon with douglas fir trees growing in the shade that were not able to make as much sugars through photosynthesis.

Conversely, after leaf drop in the autumn, the evergreen douglas fir trees gave carbon to birch trees that could no longer photosynthesize their own sugars because they didn’t have leaves.

Surprisingly, this relationship wasn’t the same with some of the other tree species. For example, Simard found that cedar trees and paper birch did not share nutrients. Interestingly, these two trees in nature would normally not be occupying the same habitat.

Dr. Simard’s also discovered that the old trees in a forest have a special nurturing role toward younger trees. She called these old trees hub trees or mother trees. In the case of the douglas fir, the hub tree would be the center of a vast network of below ground mycorrhizal fungi. These hub trees would inoculate douglas fir seedlings with the beneficial fungi and give them nutrients to nurse them along.

She found that the hub trees would share nutrients with all douglas fir seedlings, but would somehow recognize their own offspring and share much more nutrients with them. They would even make room in their root system for the developing root system of the young tree.

The relationship is especially important in a climax forest in which there is not much available sunlight for trees growing in heavy shade.

Douglas fir resembles our eastern hemlock in many ways. So you can imagine why it might be important for a mother tree to share nutrients with younger trees in the heavy shade of a forest such as a hemlock forest.

Lastly, Dr. Simard discovered that old-growth hub trees recognize when they are dying and send as many nutrients as possible to the other trees in their mycorrhizal network before they die.

All of this nutrient sharing between trees appears to occur through the vast web of the mycorrhizal fungi connecting the trees under the surface of the ground.

Over the past few years, I have developed an appreciation for the web of life under the surface of the forest floor that supports the tree and other plant life. This complexity of the community of microorganisms in a forest intrigues and amazes me.

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