‘Mother Trees’ Are Intelligent: They Learn and Remember
Few researchers have had the pop culture impact of Suzanne Simard. What captured the public’s imagination was Simard’s findings that trees are social beings that exchange nutrients, help one another.
Simard used radioactive isotopes of carbon to trace how trees share resources and information with one another through an intricately interconnected network of mycorrhizal fungi that colonize trees’ roots. In more recent work, she has found evidence that trees recognize their own kin and favour them with the lion’s share of their bounty, especially when the saplings are most vulnerable. She argues that forests are not collections of isolated organisms but webs of constantly evolving relationships.
Webs of relationships
She says that we humans have been harming these webs, through clear-cutting and fire suppression. Now we are causing climate change faster than trees can adapt, causing species to go extinct and a sharp increase in pests such as the bark beetles that have devastated forests throughout western North America.
She says that people can take many actions to help forests—the world’s largest terrestrial carbon sink—recover and, in doing so, slow global warming. One of her most unconventional ideas is the pivotal role that the ancient giants she calls “mother trees” play in the ecosystem and our need to zealously protect them.
Growing up in a logging family in rural British Columbia she was spending time in the forest as a child she knew that everything is entwined and overlapping, things growing right next to each other. ”It was always this incredibly connected place, even though I wouldn’t have been able to articulate that as a child.”
In British Columbia today, loggers sacrifice birches and broadleaf trees, which they see as competing for sun and nutrients with the firs they harvest. As a tree scientist she discovered that the birches were actually feeding the fir seedlings, keeping them alive.
Providing nutrients
She was sent in to find out why some of the firs in the tree plantations were not doing as well as the healthy young fir trees in the natural forest. One thing she found is that in the natural forest, the more the birch trees shaded the Douglas fir seedlings, the more carbon in the form of photosynthetic sugars the birches provided to them through the mycorrhizal network belowground. Birches are also full of nitrogen, which in turn supports bacteria that do all the work of cycling nutrients and creating antibiotics and other chemicals in the soil that counter pathogens and help to produce a balanced ecosystem.
Protecting trees
Birches supply carbon and nitrogen to the soil, exuded by the roots and mycorrhizae, and this provides energy for bacteria in the soil to grow. One species of bacteria that grows in the rhizosphere of birch roots is a fluorescent pseudomonad. She conducted lab studies to show that these bacteria inhibit the growth of a pathogenic fungus that attacks firs and to a lesser extent birch.
<Forest of birches and firs
Exchanging nutrients
She also found that birches give sugars to fir trees in the summer through the mycorrhizal networks and that firs return the favour by sending food to birches in the spring and fall, when the birches lack leaves.
Some scientist were having trouble with this: Why would a tree send photosynthetic sugars to another species? But to her that was so obvious. They are all helping one another to create a healthy community that is of benefit to everyone.
Biodiversity brings stability
Studies show that biodiversity leads to stability—it leads to resilience, and it’s easy to see why. Species collaborate. It’s a synergistic system. One plant has a high photosynthetic capacity, and it fuels all these soil bacteria that fix nitrogen. Then there’s this other deep-rooted plant, and it goes down and brings up water, which it shares with the nitrogen-fixing plant because that nitrogen plant needs a lot of water to carry out its activities. So the whole productivity of the ecosystem goes way up.
Because the species are helping one another. This is an important concept that we all need to learn about and embrace. It’s one that has evaded us.
Cooperation is important
So cooperation is equally important to, if not more important than, competition. Do we need to revise our views about how nature operates?
We do. Charles Darwin also understood the importance of cooperation. He knew that plants lived together in communities, and he wrote about it. It’s just that it never got the same traction as his natural-selection-based-on-competition theory.
Nowadays we look at things like the human genome and realize that a lot of our DNA is of viral or bacterial origin. We now know that we ourselves are consortiums of species that evolved together. It’s becoming more mainstream to think that way.
Forests are multispecies organizations. Aboriginal cultures knew about these linkages and interactions and how sophisticated they were. Humans haven’t always had this reductionist approach. It’s a development of Western science that led us to this.
More holistic
Western science has focused too much on the individual organism and not enough on the functioning of the larger community. There’s been a progression in the science. We started very simply: we looked at single organisms, then we looked at single species, then we started to look at communities of species and then at ecosystems and then at even higher levels of organization. So Western science has gone from the simple to the complex. It’s changed naturally as we’ve become more sophisticated ourselves. It’s become more holistic.
Intelligent trees?
Her use of the word “intelligent” to describe trees is controversial. But she is making an even more radical assertion—that there is an “intelligence” in the ecosystem as a whole. People find it “controversial” because of using a human term to describe a highly evolved system, our brain, but actually a forest ecosystem has structures that are very similar to our brain. They are not brains, yet they have all the characteristics of intelligence: the behaviours, the responses, the perceptions, the learning, the archiving of memory. And what is being sent through those networks are chemicals like glutamate, which is an amino acid that also serves as a neurotransmitter in our brain. She calls the system “intelligent” because it is the most analogous word that she can find in the English language to describe what she is seeing.
Memory of trees?
The memory of past events is stored in the tree rings and in DNA of the seeds. The width and density of the tree rings, as well as the natural abundance of certain isotopes, holds the memories of growing conditions of previous years, such as whether it was a wet or dry year, or whether there were nearby trees, or if they had blown over, creating more space for the trees to grow faster. In the seeds, the DNA evolves through mutations, as well as epigenetics, reflecting genetic adaptations to changing environmental conditions.
The Mother Tree Project.
Mother trees are the biggest, oldest trees in the forest. They are the glue that holds the forest together. They have the genes from previous climates; they are homes to so many creatures, so much biodiversity. Through their huge photosynthetic capacity, they provide food for the whole soil web of life. They keep carbon in the soil and aboveground, and they keep the water flowing. These ancient trees help forest recover from disturbances. We can’t afford to lose them.
The way forests are organized, they can recover really quickly. You can push them to the point of collapse, but they have a huge buffering capacity.
The Mother Tree Project is trying to apply these concepts in real forests so that we can begin to manage forests for resilience, biodiversity and health, recognizing that we’ve actually pushed them to the brink of collapse with climate change and overharvesting.
Helping nature
But right now with climate change, we’re going to need to help nature along a bit. We have to make sure the mother trees are there to help the next generation come forward. We have to move some genotypes that are preadapted to a warmer climate into more northerly or higher-elevation forests that are rapidly warming. The velocity of climate change is far faster than the velocity at which trees can migrate on their own or adapt.
Although regeneration of locally adapted seed is the best, we have changed climate so rapidly that forests will need help to survive and reproduce. We have to assist in the migration of seeds already preadapted from warmer climates. We need to become active agents of change—productive agents instead of exploiters.
Adapted from an article in Scientific American online by Richard Schiffman, May 2021
Read more about this:
Suzanne Simard: Finding the Mother Tree: Discovering the Wisdom of the Forest (Allen Lane, 2021)
Peter Wohlleben: The Hidden Life of Trees (Harper Collins, 2017)