摘要：First she discovered the wood wide web. Now Suzanne Simard has found that underground connections in a forest are like a brain that allows trees to form societies – and look out for their kin
Suzanne Simard was raised in the Monashee mountains in British Columbia, Canada. Her research, beginning with the discovery of the wood wide web, has transformed our understanding of forests. She is now a professor of forest ecology at the University of British Columbia.
FEW scientists make much impact with their PhD thesis, but, in 1997, Suzanne Simard did just that. She had discovered that forest trees share and trade food via fungal networks that connect their roots. Her research on “the wood wide web” made the cover of Nature. What was then a challenge to orthodox ideas is today widely accepted.
But Simard and her colleagues continue to challenge our preconceptions of how plants interact. Among other things, their research shows that the wood wide web is like a brain and can communicate information throughout the entire forest, that trees recognise their offspring and nurture them and that lessons learned from past experiences can be transmitted from old trees to young ones.
Simard calls herself a “forest detective”. Her childhood was spent in the woods of British Columbia, Canada, where her family had made a living as foresters for generations. As a young woman, she joined the family profession, but soon realised that modern forestry practices were threatening the survival of the ecosystem she loved. She knew that, when logged with a lighter touch, forests can heal themselves, and she set out to discover how they are so naturally resilient. Along the way, her concern for the future of forests sparked an intense curiosity about what makes them tick.
Simard is now a professor in the faculty of forestry at the University of British Columbia. Her new book, Finding the Mother Tree: Uncovering the wisdom and intelligence of the forest, tells how – like trees in a forest – her life and research are intricately intertwined.
Rowan Hooper: How did your discovery of the wood wide web change the received wisdom about forests?
Suzanne Simard: The key finding is that trees are in a connected society, and that it’s a physical network and that they trade and collaborate and interact in really sophisticated ways as a cohesive, holistic society. From my training, and from the way we viewed forests or any plant community prior to that – at least in Western thinking – we didn’t see plants as collaborative and linking. We thought that plants are solitary and compete to acquire as many resources as they can to increase their fitness. That idea isn’t necessarily wrong. It’s just that the way plants grow isn’t simply by competition. They also collaborate, and there are synergies.
The wood wide web consists of fungi as well as tree roots. What are fungi in thesemycorrhizal networkslike?
There are many different species of fungi, and they have niches and different physical and physiological structures. Some are really big pipelines. Some are little – tiny, fine threads. They all have different roles in extracting resources and moving things around. If you change the composition of that fungal community, you actually change how nutrients and carbon and water are moved around.
At first, some biologists were sceptical about the wood wide web. How did you convince them?
It was so tiring. I had to keep showing that these networks exist, and that plants are obligate mutualists with fungi; this means they need them to gather nutrients and water from the soil, especially in a stressful environment. That is what all seeds encounter when they are trying to germinate. The environment is a stressful place because seeds are small, there are predators, competitors – there’s all sorts going on. And this little boost, the boost provided by the fungi, even though it’s hard to measure, can make the difference between survival or death.
This doesn’t challenge natural selection at all. Darwin wrote about the importance of collaboration in communities. It’s just that it didn’t gain traction like the idea of competition did. Natural selection results from more than competition. It involves a lot of different interactions and relationships between species and with the environment.
Richard Powers fictionalised your struggle in his arboreal novelThe Overstory. Did his account ring true?
Powers did such a great job. He was able to construct this character, and I thought that he really captured it well. Even though Patricia Westerford studied above-ground communication and I was studying below ground, that didn’t really matter. All the personal things about the difficulties in advancing her ideas and getting her work out there, I encountered something in parallel.
The pushback against your work reminds me of the reactionJames Lovelock’sGaia hypothesis received. Do you agree?
I think it comes back to the fact that there had been this separation of humanity from nature, mind from body, spirit from intellect, and that we had moved away from this more holistic, spiritual way of seeing the world. Lovelock’s idea of the biosphere as a self-regulating system was antithetical to the view that we could dissect the world and understand all the parts in a deterministic way. It was similar with Lynn Margulis and her endosymbiotic theory, showing how eukaryotic cells evolved from the engulfment and collaboration between different prokaryotic cells. She was ridiculed and her papers were rejected – but now her ideas are mainstream.
You have continued to make remarkable discoveries. How did you find out that trees recognise their family members?
I was working on mycorrhizal networks, seeing if the networks were improving regeneration of seedlings around trees. And it seemed like the next logical question was: well, would the networks be able to favour seedlings that were coming from the mother trees, the parent trees? I worked with Susan Dudley at McMaster University [in Canada] and we have found that kin recognition occurs in conifers. It’s happening through mycorrhizal networks, and it’s an important phenomenon in structuring these forest communities.
We were able to trace the carbon transferred between trees. We would label a mother or a sibling plant [by feeding it with carbon dioxide that contained a radioactive form of carbon] and then we would see that the carbon would transmit to a kin seedling, but not to a stranger planted nearby. I don’t know how they recognise their kin, but I assume it’s by chemicals because when we allow seedlings to connect with the mother trees or with their siblings, through these mycorrhizal networks, we get responses much more dramatically than if they connect with non-kin. It changes the rooting behaviour. It changes their chemistry, the nutrition of the plants and the response to disease.
All this reminds me of the “mother tree” in Avatar, a film featuring an alien species that can tap into something like a forest-wide natural network. Were you involved with that?
It’s funny, when the movie came out, I got a call from someone who said that [director] James Cameron based his idea of the film’s “hometree” and the Na’vi people connecting to the network on my work. I was like: “Oh, really? That’s cool. I’m glad somebody picked it up.” And then when I went to see the movie, I’m just like: “Oh my god, of course he read my papers.” Interestingly enough, James Cameron is making sequels to Avatar right now, and they’re making a documentary on the science behind Avatar. And now they’ve contacted me.
Your latest findings are even more mind-blowing. Tell us what you discovered when you mapped the nodes and connections in mycorrhizal networks.
The architecture of those networks follows a biological neural network. In your brain, neurotransmitters have got to move from different lobes in order for your thought patterns to emerge. So they have evolved to do that efficiently.
It turns out, the underground network in the forest is designed the same way. I think it’s for efficient transfer of information and resources for the health of the full community. Not only that, but the chemicals that are moving in those networks include glutamate, which is one of the dominant neurotransmitters in brains.
Is it too much to suggest that, like in a brain, there is intelligence in this network, even wisdom?
From a purely biological, physical analysis, it looked like it had the hallmarks of intelligence. Not just the communication of information and changes in behaviour as a result, but just the pure, evolved, biological chemistry and the shape of the networks themselves spoke to the idea that they were wired and designed for wisdom.
If you look at the sophisticated interactions between plants – and some of that happens through the networks – their ability to respond and change their behaviours according to this information all speaks of wisdom to me.
What about awareness? Are trees aware of us?
Plants are attuned to any kind of disturbance or injury, and we can measure their biochemical responses to that. We know that certain biochemical pathways are triggered to develop these cascades of chemicals that are responses to stresses and disturbances, like chewing by herbivores. And if they are so attuned to small injuries like that, why wouldn’t they be attuned to us? We’re the dominant disturbance agent in forests. We cut down trees. We girdle them. We tap them.
If I injure trees so much that they start to die, they start sending their carbon through their roots to their neighbours. They are responsive to us. We’ve proven it by doing our experiments. People go: “Oh, that’s kind of scary”. But why wouldn’t plants be aware of people? They are aware of everything else.
That might surprise some people in the West, but not the Indigenous communities in North America with which you collaborate. How do they see the forest?
The work I do about trees being connected and nurturing each other represents a world view that has been known for thousands of years by the Aboriginal people of North America. But there’s been this long history of ignoring them and ridiculing them and destroying them. Maybe we won’t listen to Aboriginal people because we think it’s mystical and airy-fairy and spiritual, and that we really only want science, but I’ve been able to demonstrate some of these holistic connections with science. We’re doing the same things. We have the same findings and world views. So let’s work as a team.
How has your upbringing shaped your own views?
I grew up in the forest, seeing how it was this diverse, entwined, very complex place where all these creatures live together. The trees, the roots overlapping, the many species growing together, the lush, structured forest – that was what I knew. My family are foresters, and when I started getting involved as a forester, there was a big shift going on in industrial practices, with clear-cutting [felling all the trees in an area]. Intuitively, it didn’t make sense to me.
Have things got better now that we know about the connections in forests?
We know a ton about how to make it better, and there are definitely people who want to make it better. There’s a lot of pressure to improve practices, and we even have certification of our forests to show that we do sustainable forestry practices. But look at the big picture in British Columbia. We’ve turned, in my short lifetime, from a province of old-growth forest to a province full of clear cuts. Even the iconic old-growth forests with the big cedars and hemlocks and spruces on the west coast, those towering forests, only about 3 per cent are left. We’ve cut everything down, and it’s not stopping.
So, no, it hasn’t improved. In some ways, it’s got a lot worse. And I think that this is manifested in these big indicators, which are climate change and loss of biodiversity. A lot of that comes from forestry practices.
Should there be some sort of charter for trees, akin to animal rights or human rights?
That’s a great idea, yes. We have the United Nations Convention on Conservation of Biodiversity and we’ve got the Paris Agreement on climate change. Conservation of forests is crucial to both of those things. So we have treaties and yet we don’t honour them. The iconic old-growth forests are hugely diverse and store megatons of carbon. Those forests aren’t very well protected and they aren’t protected far into the future. When we push the system to collapse – which is what we’re doing if we lose those old-growth forests – what are we going to do? They are the places where that genetic diversity lives, that we are going to depend on in order to get us through climate change.
What would you like people to do after hearing about your work or reading your book?
I want them to want to go to the forest. That’s the most simple, basic thing. Just go and be with it and love it and care for it and talk to it and show your respect for it. I think that is the foundation of changing our behaviours. Ultimately, this will translate into action. Not everybody will act, of course, and not everybody has to act. But we need that change to happen, and it starts with connecting back with nature.
Every forest has its share of mature, majestic trees. Forest ecologist Suzanne Simard at the University of British Columbia, Canada, calls these “mother trees”. She and her colleagues have found that they are crucial to the well-being of the entire forest community. They are the hubs of communication, protection and sentience, they nurture their own offspring and they provide information to help generations of trees survive. This has crucial implications for the way we manage forests, which is why, in 2016, Simard launched The Mother Tree Project to explore the role that mother trees play in forest regeneration.
“It’s the biggest project I’ve ever done,” says Simard. It involves 24 Douglas fir forests stretching across nine climate regions in British Columbia. Each forest is logged using five different harvesting treatments, ranging from felling all the trees in an area to keeping large patches of trees with mother trees present. The team monitors and measures how the forest responds and regenerates by collecting information before and after logging about things like carbon storage, biodiversity and productivity.
Research is ongoing, but there have already been some compelling results. “We’ve found that the more mother trees we leave, the more diverse and abundant the natural regeneration is,” says Simard. Her team also has good evidence that mother trees protect seedlings, especially when conditions get tough, such as when there is a frost or a particularly hot, dry day. By comparing results in different climate regions, the researchers aim to identify more sustainable ways to manage forests in the face of climate change.
“I wanted to create a project that would show people that you can do things in a different way and design forest practices around the idea that the forest is a connected, nurturing, healing place,” says Simard.