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Chapter 1: What is the 'Wood Wide Web' and why is it significant?
Over the past 25 years, scientists have presented us with a captivating, almost Disney-esque tale. Imagine a diverse and vibrant forest, filled with trees of different ages and species, all thriving in the sunlight that powers their cellular functions. But hidden beneath the surface, intertwined within their roots, are thin, hair-like strands of a different kingdom altogether.
These branching structures serve not only to expand the reach of each individual tree, but they connect multiple trees together, allowing messages to be communicated in a buzzing multi-server system akin to the invention that changed the course of human civilization, the internet. Welcome to the Wood Wide Web. I'm James Stewart and you're watching Astrum Earth.
Now buckle up, because we're about to recount a scientific tale with more twists, turns and knots than an old oak tree. The discovery of the wood wide web mesmerised the public as much as the internet itself, resulting in the publication of countless popular science articles, books, documentaries, films, podcasts and more. But is there more to the story?
A growing number of scientists certainly seem to think so, and the result has been a bitter academic war that still continues to this day.
Chapter 2: How did Suzanne Simard's research change our understanding of trees?
In this video, join me as we uncover the whole story behind the famed Wood Wide Web, where it all began, its impact on conservation, and the wealth of research it inspired into the secret lives of our wooden friends. Our story begins in the temperate forests of British Columbia in Canada.
Suzanne Simard is about to make a discovery that will help her to achieve the near impossible with her PhD thesis, making the cover of nature. In 1997, her article was published with the title Net Transfer of Carbon between ectomycorrhizal tree species in the field, which is fairly unassuming considering the content of this paper.
In essence, Simard was claiming to have observed the transfer of carbon between seedlings of paper birch and Douglas fir in the field through a shared fungal connection between their root systems. Not just any old fungus can form a connection with trees. This privilege is mostly reserved for mycorrhizal fungi.
The term mycorrhizal fungi refers to a broad group of species that have been forming beneficial partnerships with plants for over 450 million years.
Their name comes from the Greek myx meaning fungi and rhiza meaning root, which is accurate because these fungi form their relationships with the roots of their plant partners, extending the reach of the plants through a fungal network called the mycelium.
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Chapter 3: What role do mycorrhizal fungi play in tree communication?
These networks are so vast, it's estimated that every one kilogram of soil can contain up to 200 kilometers of fungal strands. And some individual fungi can extend across a hundred square meters. With this impressive reach, the fungus can help its plant friends to absorb more nutrients from the soil in exchange for some of their sugars.
This is an example of symbiosis, because both parties get something good out of the relationship. Now, scientists already knew about this network at the time of Simard's research. All the way back in 1885, the German plant biologist Albert Bernard Frank wrote a paper describing the symbiosis between plant roots and mycorrhizal fungi in Prussian truffle districts.
And throughout the 20th century, scientists had documented the transfer of carbon, nitrogen, and phosphorus through fungal connections in lab experiments. But what made Simard's discovery so exciting was that she claimed to have seen trees using this network to transfer carbon out in the forest, which was a big deal.
In the forest there are far more variables at play, some of which are near impossible to replicate in a lab study. anything that you observe in these natural environments is a far more realistic snapshot of what is really going on. So it's often the final piece of evidence needed to prove a theory. This was no different for the theory of a woods wide web.
Scientists knew it existed and had some idea of what it could do. But for many, Simard's research provided definitive evidence that these ideas hold true for real world habitats. Now, as I'm sure you're wondering, how did she do it? Well, the study looked at paper birch and the Douglas fir trees because they are known to make the same type of fungal connections.
Each seedling was given a dose of carbon dioxide gas, which was labelled with different isotopes of carbon, so the team could track where this carbon ended up. On top of this, the Douglas fir was kept in the shade so that it would make less of its own sugars by photosynthesis. The experiment ran for two growing seasons and the results were astounding.
Simard found that the labeled carbon dioxide had been converted into sugars by photosynthesis in the paper birch, then transferred to the Douglas fir through their fungal link.
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Chapter 4: What evidence supports the concept of resource sharing among trees?
Some carbon had travelled in the other direction too, but since the Douglas fir was struggling to make sugars in the shade, the paper birch had transferred more carbon to it overall, resulting in a net carbon gain in the Douglas fir. In other words, these trees weren't just going Dutch and splitting their carbon equally, the paper birch was giving extra carbon to the Douglas fir.
The team were shocked by this result and naturally started coming up with some ideas as to why the paper birch was being so generous. This led them to wonder, could it somehow sense that the Douglas fir wasn't making as much carbon on its own? This theory was outrageous. it seemed to tear apart the widely accepted concept of survival of the fittest.
Instead of everyone looking out for themselves, we're talking about two different species helping each other via a shared connection with a third, even more distantly related species. Though they are different, these tree species are competing for the same resources. Light, space, water and nutrients. So why don't they just keep everything for themselves?
Could it be that they share because their generosity will eventually be returned by another member of the forest? Simard's findings suggested that trees formed far closer-knit communities than we once thought, and that resources were shared to boost the overall health of the forest, aided by some seriously helpful fungi, of course.
Printed on the cover page of Nature, with the catchy slogan Wood Wide Web, this discovery caused quite the stir.
And the idea that trees had beaten us to the punch with their own internet, with wooden servers and fungal routers, really caught on. There were articles on the hidden language of trees, manuals on deciphering tree feelings, documentaries, TED Talks, and bizarrely, even a name drop for Simard in the hit show, Ted Lasso.
If you look at the use of the phrase Wood Wide Web in publications between 1997 and 2022, you can see an exponential increase in popularity from the early 2000s. The Wood Wide Web had even spun its silk over Hollywood, with Amy Adams set to star as Simard in the feature film adaption of her research career. The world, it seemed, had gone tree crazy.
But Simard took things one step further, publishing a book titled Finding the Mother Tree in 2021. The book is essentially a memoir, telling the story of Simard's professional and personal life against the backdrop of the Canadian forest.
Besides her 1997 research, Simard discusses her discovery that fungal networks can allow for warning signals to be communicated between trees, kin recognised, and preferential treatment applied to closer relatives. She even suggests that the fungal network in forests works like a human brain, with the fungal strands as neurons and chemical signals as neurotransmitters.
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Chapter 5: Why did some scientists begin to question the Wood Wide Web theory?
They too could speak, could provide for their kids, give preferential treatment to their friends, and maintain a social life. Amid these global shifts in perspective, it seems like the golden opportunity to seek similarities between us and the plants. In fact, these scientists were giving us the green light to do so. the world had certainly fallen in love with the wood-wide web.
But like a tree being felled, it was all about to come crashing down. Justine Kast, Jason Hoeksema, and Melanie Jones. These scientists shared something vital in common. They had all worked with Suzanne Simard at some point in their careers. Melanie Jones even co-authored the famous 1997 paper that started our story off.
Despite sharing Simar's belief in the wood wide web for years, these three tree experts had begun to get an uneasy feeling about where it was all heading, both in academic circles and the wider media. So they did what any good scientist would do and ask the difficult questions, forcing themselves to look objectively, even if that meant casting doubt on their own research. In a later interview,
Cass explained that they didn't initially set out to debunk any of Simard's claims about the Wood Wide Web.
Yeah, as a scientist, we can't pick and choose what are the good stories and the bad stories. That's sort of not our job.
Rereading the literature had forced them to face an uncomfortable truth about the fungal networks they had once put so much faith in. Unnerved by what they found, the authors voiced their concerns in an article published in 2023, to great acclaim by the rest of the science community.
This article garnered almost as much attention as the 1997 study that had inspired it, and brought the dream of the wood wide web as we knew it to an abrupt end. But what did the authors take so much issue with?
In their paper, Karst and her colleagues reviewed all research surrounding what they call common mycelial networks, which is just a more technical term for wood wide web, where mycorrhizal fungi connect the roots of the same or different plant species underground. We'll call it the network from now on to make things simpler.
They identify three common claims that have been made about these networks and sorts to review each claim in turn to see if the evidence agreed. The first one, namely that the networks are widespread in forests, was fairly simple to explore. Many mycorrhizal fungi can and do form associations with lots of different host species, which would suggest that networks are common in forests.
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Chapter 6: What were the main criticisms highlighted in the recent review of the Wood Wide Web?
The point is that even though these networks do form, we can't be sure that the links are continuous enough through time and space to make them a viable tool for communication. For all we know, the links might only last a few days, or could be too fragile to connect trees from opposite ends of the forest.
The second claim was that seedlings can use the network to share resources, like the carbon we saw earlier, in order to help them grow, and not just within the same species. This one hit especially close to home for the authors, because they had all worked with Suzanne Simard on this, and her 1997 study was the first to properly test it out in the field.
But what Karst and her colleagues started to question years later was that this behaviour doesn't seem to lie within the fungi's self-interest at all. Think about it. If you were a fungus connecting the roots of two tree species, why would you only ever funnel resources between the two trees rather than taking some for yourself?
And how is the fungus supposed to know the difference between carbon it can use for itself and carbon to be sent for Paper Birch's friend, the Douglas Fir. The authors reviewed 26 studies that claimed to prove resource transfer through the network, and found that for all of them, the results could be explained without involving the network at all.
For many, the resources could just as easily have been transferred through the soil with no need for fungal connections, and that includes the 1997 study. Similarly, the authors note that no study has actually provided proof that this transferred carbon, if it exists, actually benefits the performance of the tree receiving it. How could it?
If you were a tree with a system to generate food and farm resources on your own, why would you depend on help from an unrelated neighbor tree? One that could easily die, become disconnected, or simply stop cooperating? It doesn't seem like a very good strategy, evolution-wise. Well, the authors weren't finished there.
The final claim was that mature trees were more likely to communicate and share with their own offspring through the network, which largely covers the whole mother tree idea. And this one may be shocking because the authors actually found no published peer-reviewed evidence from forests at all to support this claim. In fact, a master's thesis from Simard's own lab actually found the opposite.
as Douglas firs placed in a shared fungal network were less likely to survive if they were close to their older genetic relatives in the field. Even more uncomfortable is that Simard made a narrative choice to write in her book that the grad student had found support for her theory, even though she has since denied that she was deliberately misleading her readers.
To top off their review, Kast and her colleagues looked to see whether there had been any bias in the literature surrounding the network. They identified 18 studies that had been influential in this field, and looked at how they were used in subsequent research.
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Chapter 7: How do trees communicate using volatile organic compounds (VOCs)?
In research, wording is everything, and evidence suggesting that networks can form is not the same as evidence that they do form in complex real-world habitats. But you can see how that kind of positive bias is a bit of a runaway train. And if even published researchers are doing it, then it's bound to happen in the mainstream media too.
As you may expect, Simard wasn't too pleased when the Wood Wide Web began to unravel at her feet, calling Kast's review paper an injustice to the whole world, no less. She labeled all the critics as reductionist scientists and has since published response articles pushing back on some of their arguments.
Now, although we're often quick to take sides during a drama, it's important to note that there are no heroes and villains in this story. Some scientists may disagree with Simard's stance, but others don't. And if nothing else, Simard has done good work for the forest too.
Her 2015 Mother Tree project is a research initiative aimed to protect the biodiversity of British Columbia woodlands, drawing on indigenous knowledge and changing forestry practices in North America to be more sustainable.
These are admirable goals, goals which we can agree are probably good for conservation regardless of whether the person advocating for them believes in the wood wide web or not. Like many scientific arguments, the situation has become messy, with researchers picking at details and scrabbling to express where they stand on the matter.
Unfortunately, by the time the smoke clears on this debate, the public may have lost interest in the result, and scientists will definitely struggle to garner the same kind of enthusiasm that once buzzed around the wood-wide web. But as Kast says, our job as scientists is to present the truth, as close as we can get to it.
Errors, misinterpretation and even overexcitement are all traps that scientists and the media reporting their findings can fall into. We are all human after all. So we need to always be open to reflect objectively and update our presentation of truth as we gain new insights.
And one thing scientists can all agree on, these revelations about the wood wide web should never be used to discount trees altogether or neglect their conservation. Now, with all that disillusionment behind us, it's time to move on to something more concrete, because we may be unsure about the extent of plant communication, but there is no doubt among scientists that plants do communicate.
Moving from sink to source, plant leaves can be the trigger for vital messages. Volatile organic compounds, or VOCs, encompass a large group of molecules that tend to have a low molecular mass, so they can evaporate easily and travel through the soil or air.
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Chapter 8: What lessons can we learn from the debate around the Wood Wide Web?
And scientists could be pretty sure that it was VOCs that were inducing these responses, since any efforts to block airborne signals by putting the tree branches in airtight bags meant that neighbouring trees took more damage from the herbivores. But hang on, because there's a danger here of entering into the same minefield as the wood wide web drama.
This behaviour seems too selfless to work with the principle of survival of the fittest. Why would a tree bother to send a warning signal to its neighbours whilst it was being attacked by herbivores? Wouldn't it be better for that tree if its neighbours did get damaged, since that might leave more light and other resources for itself? But consider this.
What if the damaged tree wasn't intentionally sending out a warning to help its neighbours, but the neighbours had evolved to make use of a warning that the damaged tree was releasing anyway? Scientists call this eavesdropping, and it explains these results in a way that agrees with widely accepted principles of natural selection.
Any individual plant produces many VOCs when it's attacked by herbivores to signal to itself, coordinating a response between distant branches or leaves. It is this signal, meant for communication within each individual plant, that other plants can pick up on and use to prime their own responses.
So trees have adapted to eavesdrop on their fellow trees in the forest, but perhaps more impressive is their ability to call for help during an attack from the most unlikely allies. Terpenes are a specific group within the VOCs and are responsible for that nice tree smell you get when you walk into a forest.
These molecules are also used in tree communication in response to herbivores, environmental stress and changes to the soil microbiome. In 2011, an experiment looked into how the European field elm responds to attacks from the elm leaf beetle with the help of terpenes. See, the elm leaf beetle likes to lay its eggs on the leaves of the tree, ready for the larvae to feast on them when they hatch.
but the elm has some tricks up its sleeve to combat this. They release terpenes, which seem to attract another insect, the eupholid wasp, to eat the eggs. Like insect bodyguards, they can protect the elm from damage and get a nice egg feast as a reward. The 2011 study was designed to prove whether it was the terpenes that were signaling for wasp backup.
So the authors allowed the beetles to do their thing and lay eggs on the elm, whilst treating half of the trees with chemicals that stopped them from being able to make terpenes. They then collected all the odours produced by the trees during this ordeal and presented them to the wasps to see what they'd do.
As the team suspected, the wasps spent significantly more time in the test field when the tree odours included terpenes than when terpene production had been cut off. With these results, the authors concluded that it is the turkeys that attract the wasps, and that the trees are far more skilled at fending off beetle attacks than we may give them credit for.
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