Fungi of the Bridlewood Wide Web · 6:16pm Oct 15th, 2023
Elderflower’s story of the Together Trees in Father of the Bridlewood gives me an excuse to fact-check a science story that I have been meaning to look into for a while. She says, “Together Trees communicate and connect magically to each other through their roots underground.” This sounds like something that has featured in quite a few books and documentaries in recent years—the idea that threads of fungi connect tree roots underground and allow plants to exchange nutrients and communicate. Is this true, or just an old mare’s tale invented by a batty old unicorn?
It has been mentioned in the BBC series The Green Planet and Wild Isles, the documentary film Fantastic Fungi, and books like Entangled Life by Merlin Sheldrake, and The Hidden Life of Trees by Peter Wohlleben, and others. It is a great story. But some details sound a bit too good. Nature is amazing and has surprised us in the past, but could there be some exaggeration and embellishment going on here? Time to dig a bit deeper...
The first bit seems to be well-established. Every biologist believes in fungi, that weird kingdom of life, neither plant nor animal. They are abundant in woodland, where they feed on decaying leaves and other organic matter. The mushrooms we see popping out of the ground and on old tree branches, area just their fruiting bodies, which disperse the spores. Most of the fungus is underground, consisting of long threads of mycelium, or hyphae, which can spread over a distance of many metres. When they encounter a tree root, they may link up, and establish a mutually beneficial relationship, the result of millions of years of co-evolution. The tree feeds the fungus sugars, and the fungus lets the tree access water and the nutrients. Fungi are promiscuous and in a dense forest they can hitch up with more than one tree.
So far, this all seems to be solid science. Now things get a bit more fanciful…
The mycelium threads spread through the woodland, joining up all the trees into a Wood Wide Web. The network lets the trees share resources and support each other. In times of drought, deep rooted trees can reach water and share it with young saplings. Mother trees will send water and nutrients to their children. When a tree is attacked by predators, it will send a warning signal through the network to alert those around it to the threat. The mycelium lets the trees across the forest talk to one another. The forest is a conscious sentient entity where trees work together in harmony to protect each other and all life.
Exactly how far this goes depends on which book you read.
Some details are plausible. When attacked, plants do use chemical signals to make leaves produce chemicals making them less-appetising to caterpillars. A fungal connection could let this signal spread between different plants. But does this happen often? Or just in a few isolated cases? Other details raise more questions. How does a Mother Tree address packets of plant food to her children? And how and why should the fungus deliver this to a particular recipient?
Doing a little searching, it didn’t take too long to find that these claims have been investigated and the conclusion is rather sceptical. This paper: Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests, published in Nature Ecology and Evolution this year, gives a very detailed examination of the scientific literature, specifically surveying for three claims: that the networks are widespread in forests (“support for this claim is limited… too few forests have been mapped”); that resources are transferred through networks and increase seedling performance (can happen, but not clear if it’s due to the fungi, or if it helps seedlings); and mature trees can communicate preferentially with offspring (“remains to be demonstrated”).
This is not rejecting these ideas, or challenging the results of the many studies referenced. It is just pointing out that there isn’t the evidence to back up some of the stories in the media. The main conclusion is we need more research.
What seems to be happening is that documentary producers are picking up good stories, and giving the impression that this is established scientific opinion, when it is actually an interesting idea, but a bit unlikely, and supported by little or no experimental evidence. But because it is such a good story, it is then picked up by further writer and producers, and spawns its own fanfiction. Including some crazy Avatar crossovers.
Of course, whatever happens in Bridlewood and the rest of Equestria is another story.
And that's an important step of writing fiction: knowing when to go "reality is overrated and underpowered, we're doing something different here".
I love skeptical investigation like this! I recently read a book that promoted all of these ideas, but because it was a popular account and not a scientific paper, citations were thin on the ground. It did have a fairly good bibliography, though.
My main point of concern wasn't the plausibility of the mycelium network idea itself. There are far stranger things going on in the natural world. The question that popped into my mind was, "What do the fungi get out of this relationship?" If there is no benefit to them, then the trees are... sort of parasitizing them. It take energy to move water, chemicals, and such around after all.
Sounds like a fruitful field for further study.
Teh way th papers are writtena nd offered is rather like someone taking the idea of the stock market and applying it to the farmyard? the biggest similarity is the names, after that, well, traders dont usually get kept in small pens and mucked out regularly?
One offering was that teh fungi trade resources similar to Wall Street, in that they take a cut. As in as much as they can get away with before the network collapses. Trouble is, when this happens, how can the surviving networks notice and record the events so they can moderate their behaviour, as if they were using stock market algorithms, then mass die offs would be regular and commonplace as resource availablity was drained and concetrated till most diesd of starvation, and the rest died due to toxocity?
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I guess a lot of these relationships move between parasitism and mutualism. Presumably it starts off with the fungi eating the tree root, then if the tree benefits from extra water/nutrients, it will let it stay. But it's not clear how the big networks described in some books could evolve, or if it would be stable when any individual species that takes advantage of another would benefit.
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In the long run nothing is stable in macro-scale* nature, but I know what you mean. Whenever I hear a new "scientific" claim, the first thing I ask is, "How does that work?" i.e. What is the mechanism?" If there are unknown steps, it goes in the Possible file. If the steps are clear or directly inferred, it goes in Probable. If the answer involves vaguely used words like energy, toxins, vibrations, or quantum,** it goes in the Woo-woo folder.
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* Oh ghod, proton decay.
** If the subject isn't sub-atomic physics, of course!
I had never heard of this theory but it is really interesting! Too bad it doesn't seem likely. I guess it's not really disproved, only not enough forests have been mapped? I could believe resources being distributed but not at the whim of the parent tree. The fungi helping sustain its food source though? I'd buy that.