“The Hidden Life of Trees”: They Learn and Remember

Suzanne Simard, an ecologist at the University of British Columbia, has spent years studying trees and has concluded that trees are social creatures that exchange nutrients, help each other and report on insect pests and other environmental threats.

Previous ecologists have focused on what happens above ground, but Simar used radioactive isotopes of carbon to trace how trees exchange resources and information with each other through a complex interconnected network of mycorrhizal fungi that colonize tree roots.

She found evidence that trees recognize their relatives and give them the lion’s share of their nutrients, especially when the seedlings are most vulnerable.

Simard’s first book, In Search of the Mother Tree: Discovering the Wisdom of the Forest, was released this week by Knopf Publishing. In it she argues that forests are not collections of isolated organisms, but networks of constantly evolving relationships.

Humans have been destroying these networks for years, she says, with destructive practices such as clear-cutting and controlled fires. Now, because of them, climate change is happening faster than trees can adapt, leading to species extinctions and a dramatic increase in pests like bark beetles that ravage forests in western North America.

Simard says there are many things people can do to help forests, the world’s largest terrestrial carbon sink, recover and thereby slow global climate change. Among her most unconventional ideas is the key role of ancient giants, which she calls “mother trees,” in the ecosystem and the need to protect them zealously.

In the book, Simard talks about what led her to these conclusions:

Spending time in the woods, as I did as a child in rural British Columbia, you know that everything is intertwined and intersecting, everything growing alongside each other. It’s always been an incredibly interconnected place for me, although as a child I wouldn’t have been able to articulate that.

Today in British Columbia, loggers sacrifice birch and broadleaf trees, which they believe compete for sun and nutrients with the spruce trees they harvest. I have found that the birches actually nourish the fir saplings, keeping them alive.

I was sent to find out why some spruces in forest plantations don’t grow as well as healthy young spruces in the natural forest. We found that in the natural forest, the more birch trees shaded Douglas-fir seedlings, the more carbon in the form of photosynthetic sugars the birches supplied to them through a mycorrhizal network underground.

The birch trees also have plenty of nitrogen, which in turn supports the bacteria that do all the work of nutrient cycling and creating antibiotics and other chemicals in the soil that resist pathogens and help create a balanced ecosystem.

Birch trees supply carbon and nitrogen to the soil from their roots and mycorrhiza, and this provides energy for bacteria to grow in the soil. One species of bacteria that grows in the rhizosphere of birch roots is fluorescent pseudomonad. I did laboratory research and found that this bacterium, when placed in a medium with Armillaria ostoyae, a pathogenic fungus that affects spruce and to a lesser extent birch, suppresses the growth of the fungus.

I’ve also found that birches give sugars to spruces in the summer through mycorrhizal networks, and spruces respond by sending food to birches in the spring and fall, when birches have no leaves.

Isn’t that great? This has caused some scientists difficulty: Why would a tree send photosynthetic sugars to another species? And to me it was so obvious. They all help each other to create a healthy community that benefits everyone.

Forest communities are, in some ways, more efficient than our own society.

Their relationships promote diversity. Research shows that biodiversity leads to stability – it leads to sustainability, and it’s easy to see why. Species cooperate. It’s a synergistic system. One plant has a high capacity for photosynthesis, and it feeds all these soil bacteria that fix nitrogen.

Then another deep-rooted plant comes along and goes down and brings in water, which it shares with the nitrogen-fixing plant because the nitrogen-fixing plant needs a lot of water to do its activities. And suddenly the productivity of the whole ecosystem increases dramatically. Because the species help each other.

This is a very important concept that we all need to learn about and accept. It is a concept that eludes us. Cooperation is just as important as competition, if not more important.

It’s time we reexamine our views on how nature works.

Charles Darwin also understood the importance of cooperation. He knew that plants lived together in communities and wrote about it. It’s just that this theory didn’t get as much traction as his theory of competition based on natural selection.

Today we look at things like the human genome and realize that much of our DNA is of viral or bacterial origin. We now know that we ourselves are a consortium of species that have evolved together. This is becoming more and more popular thinking. Similarly, forests are multi-species organizations. Aboriginal cultures were aware of these relationships and interactions and how complex they were. Humans didn’t always have this reductionist approach. It is the development of Western science that has led us to this.

Western science focuses too much on the individual organism and not enough on the functioning of the larger community.

Many scientists accustomed to “accepted theories” don’t like the fact that I use the term “intelligent” to describe trees. But I argue that it is much more complicated than that, and that there is “intelligence” in the ecosystem as a whole.

This comes from the fact that I use the human term “intelligent” to describe a highly evolved system that works and has structures very similar to our brains. It’s not a brain, but they have all the characteristics of intelligence: behavior, reaction, perception, learning, memory storage. And what is transmitted through these networks are [chemicals] like glutamate, which is an amino acid and serves as a neurotransmitter in our brain. I call this system “intelligent” because it is the most appropriate word I can find in the English language to describe what I see.

Some scientists dispute my use of words like “memory. I do believe that trees do “remember” what happened to them.

The memory of past events is stored in tree rings and in the DNA of the seeds. The width and density of tree rings and the natural abundance of certain isotopes store memories of growing conditions in previous years, such as whether it was a wet or dry year, whether there were trees nearby, or whether they disappeared, creating more room for trees to grow quickly. In seeds, DNA evolves through mutations as well as epigenetics, reflecting genetic adaptation to changing environmental conditions.

As scientists, we get very strong training. It can be pretty tough. There are very rigid experimental schemes. I couldn’t just go and observe something-they wouldn’t publish my work. I had to use these experimental schemes-and I did. But my observations were always so important to me to ask the questions I was asking. They always came from the way I grew up, the way I saw the forest, what I observed.

My latest research paper is called “The Mother Trees Project.” What are “mother trees”?

Mother trees are the largest and oldest trees in the forest. They are the glue that holds the forest together. They retain genes from previous climates; they are home to so many creatures, so much biodiversity. Because of their enormous capacity for photosynthesis, they provide food for the entire soil network of life. They retain carbon in the soil and above ground, and also maintain water flow. These ancient trees help forests recover from disturbance. We can’t afford to lose them.

The Mother Tree Project is trying to apply these concepts to real forests so that we can begin to manage forests for their sustainability, biodiversity, and health, realizing that we have actually brought them to the brink of destruction due to climate change and over-cutting. We are currently working in nine forests that stretch 900 kilometers from the U.S.-Canada border to Fort St. James, which is about halfway across British Columbia.

I have no time for discouragement. When I started studying these forest systems, I realized that because of the way they are arranged, they can recover very quickly. You can drive them to collapse, but they have tremendous buffering capacity. I mean, nature is genius, right?

But the difference now is that with climate change, we’re going to have to help nature a little bit. We have to make sure that the mother trees will be there to help the next generation. We will have to move some genotypes adapted to warmer climates to more northerly or higher elevation forests that heat up quickly. The rate of climate change is much faster than the rate at which trees can migrate on their own or adapt.

While regeneration from locally adapted seeds is the best option, we have changed the climate so rapidly that forests will need help to survive and reproduce. We need to help migrate seeds already adapted to a warmer climate. We must become active agents of change – productive agents, not exploiters.

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