Carmichaels students plant trees for Arbor Day

Bureau of Forestry service forester Russell Gibbs and then Carmichaels senior Jacob Hair insert a stake next to a seedling.

We all know from life experience that animals communicate with each other through sounds, expressions and gestures. For example, if you have a dog, I bet it is pretty good at letting you know when it needs to go out, when it wants to play, or when someone is coming up the driveway.

Well, as far as we know, trees don’t make sounds or gestures, but we are learning they sure do talk.

You see, under the soil there is a vast network of fungi that create lattices of threads or mycelium. The fungi bring water and nutrients to the tree and in return the tree gives them sugars and other products of their photosynthesis.

This is called a symbiotic relationship - it’s a win-win.

Trees use the network of fungi created threads, called the “wood wide web” to talk to each other. Dr. Suzanne Simard of the University of British Columbia coined this term to describe this relationship.

For example, say a caterpillar is eating a tree’s leaves or sucking its sap or burrowing into its trunk. That tree can emit a volatile compound into the air that attracts the wasps and flies that kill that type of caterpillar. The tree can also send an alert signal through the "wood wide web" so that surrounding trees also prophylactically emit the same volatile compound to keep themselves safe from attack.

Let’s also say a young Douglas fir is struggling because it is too shaded for photosynthesis to make all the nutrients it needs to survive and thrive. It can communicate its need to surrounding trees through the "wood wide web." A birch tree getting plenty of light picks up the signal and in response sends its extra nutrients over to the Douglas fir, enabling it to grow taller and get more light. Come the fall, when the birch loses its leaves, the evergreen Douglas fir returns the favor.

Just like neighbors borrowing cups of sugar.

Whether a tree’s “talk” is kind or cruel depends on your perspective. Are you the invasive plant or the caterpillar that gets killed by a tree summoning predators or are you the struggling sapling that is given needed extra nourishment by a neighboring tree?

As a second example of not all plant communication having “kind” effects, the black walnut tree is prized by many for its wood, nut and landscaping value. On the other hand, perhaps as a form of self protection, nearly all parts of the black walnut are toxic to many plants who try to root nearby and many animals who try to eat the bark or leaves. This is because of a substance called juglone produced by the black walnut.

And trees aren’t the only plants known to talk.

Research has found the same types of communication in grasses, bean and tobacco plants. And they’ve documented the communication in response to several types of dangers including invasive plants, spider mites, caterpillars, hand plucking of leaves and deforestation. The results are found in both laboratory experiments and controlled observations in nature. Kind of gives a new appreciation for the life all around us, doesn’t it?

Lewis is a Penn State Extension master gardener.

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