Over the past 25 years, scientists have
presented us with a captivating, almost
Disneyesque 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-service system, akin to the
invention that changed the course of
human civilization,
the internet.
Welcome to the woodwide web.
I'm James Stewart and you're watching
Astramm 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
woodwide web mesmerized 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. In this video,
join me as we uncover the whole story
behind the famed woodwide 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
ectoicroisal 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 fur 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 microisal fungi. The
term microisal 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 mics meaning fungi and
riser meaning root which is accurate
because these fungi form their
relationships with the roots of their
plant partners extending the reach of
the plant through a fungal network
called the mcelium.
These networks are so vast, it's
estimated that every 1 kg of soil can
contain up to 200 km of fungal strands.
And some individual fungi can extend
across 100 square m.
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
microisal 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 Sim'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 woodswide web. Scientists knew it
existed and had some idea of what it
could do, but for many, Sim's research
provided definitive evidence that these
ideas hold true for realworld habitats.
Now, as I'm sure you're wondering, how
did she do it?
Well, the study looked at paper birch
and the Douglas fur 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 labeled with different
isotopes of carbon, so the team could
track where this carbon ended up. On top
of this, the Douglas fur 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.
Sim found that the labeled carbon
dioxide had been converted into sugars
by photosynthesis in the paper birch,
then transferred to the Douglas fur
through their fungal link. Some carbon
had traveled in the other direction,
too. But since the Douglas fur 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 fur. 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 fur.
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 fur 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?
Simod's findings suggested that trees
formed far closeknit communities than we
once thought and that resources were
shared to boost the overall health of
the forest, aided by some seriously
helpful fungy of course.
Printed on the cover page of nature with
the catchy slogan woodwide 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 rooters 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
woodwide web in publications between
1997 and 2022, you can see an
exponential increase in popularity from
the early 2000s. The woodwide 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 Simar 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 Simar's professional and personal
life against the backdrop of the
Canadian forest. Besides her 1997
research, Simar discusses her discovery
that fungal networks can allow for
warning signals to be communicated
between trees, kin recognized, 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.
This concept transforms the forest into
an ecosystem where no tree stands alone
and familiar bonds can get you through
hard times. With a picture like that,
who wouldn't have the urge to run to the
nearest forest and hug a mother tree?
It certainly was a beautiful idea that
organisms from totally different
kingdoms, plante and fungi, could come
together in symbiosis to promote
communication across the entire forest.
It had the potential to revolutionize
the way we thought about conservation
going forward. More emphasis could be
placed on maintaining mother trees in
the forest.
But perhaps even more revolutionary was
the idea that trees were more like us
than we thought. 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 woodswide web, but like a tree
being failed, it was all about to come
crashing down.
Justine cast, Jason Hookimmer, 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
Simard's belief in the woodwide 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 doubts 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 woodw white
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 greater claim 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
woodwide web as we knew it to an abrupt
end.
But what did the authors take so much
issue with? In their paper, Cast and her
colleagues reviewed all research
surrounding what they call common
mcelial networks, which is just a more
technical term for woodwide web, where
microisal 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
soughts 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 microisal fungi can and
do form associations with lots of
different host species, which would
suggest that networks are common in
forests. However, there is a problem
because we can't really observe these
networks in situ that is in the forest
itself, as you would damage and fragment
it before you could tell whether it was
one continuous connection or not. Each
fungal strand is only about the width of
a human hair after all. There has been
research mapping the presence of
microisal fungi using techniques like
machine learning. But to actually know
whether these fungi link together in one
big continuous network across a forest,
well, scientists would need to analyze
the DNA of the fungi and the plant roots
they attach to everywhere in the woods.
Well, at least in as many different
locations as possible to see if they
match up. It's a long, expensive, and
slow process and had only been done by
five studies for two tree species at the
time the authors were writing. 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. Now, 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 Cast and her colleagues
started to question years later was that
this behavior doesn't seem to lie within
the fungi 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 fur? The
authors reviewed 26 studies that claim
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 have 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 find 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
furs 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, Cast 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. There can
be a tendency for more positive or more
interesting results to be sized more
than those that are neutral or disagree
with the hypothesis even if methodically
the research was correct. It's called
positive citation bias and can lead to
misconceptions being spread. And sadly,
that is exactly what the authors found
in this case.
Across nearly 1,700 papers citing the 18
original studies, around 25% of them
were misinterpreting these studies as
support for claims about network
structure and 50% of them for claims
about network function.
To give just one example of this bias,
several of the 18 papers had reported
evidence that networks could form. But
many papers published later had cited
these studies as evidence the networks
were present in forests.
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, Simage wasn't too
pleased when the Woodwide Web began to
unravel at her feet, calling Cast'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 Sim's stance, but
others don't. And if nothing else, Sim
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 woodwide 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
woodwide web. But as K says, our job as
scientists is to present the truth as
close as we can get to it. Errors,
misinterpretation, and even over
excitement 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 woodwide
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 sync to source, plant leaves
can be the trigger for vital messages.
Volatile organic compounds or VOCC's
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. For several
decades now, scientists have suspected
that they play a role in tree
communication, particularly when trees
are exposed to stress.
Because trees can't just run away from
predators, they may have adapted to make
use of VOCC's as a warning signal in the
event of an attack, giving them more
time to prepare. A 2013 study cut the
leaves of willow trees to mimic the
damage caused by nibbling creatures.
This caused them to release VOCC's, and
as a result, neighboring trees were then
more likely to be munched on instead.
The same was found in another study,
this time on older trees.
They saw the same effect. But funnily
enough, trees further from the damaged
ones showed weaker resistance to
herbivores, suggesting that if a signal
was involved, there was a limit to how
far it could travel through the forest.
So, we've discussed some of the evidence
for VOCC's being used in communication,
but how did scientists piece this
together into a theory of what was
really going on?
These studies were suggesting that when
a tree is attacked by a herbivore and
damaged in some way, its neighbors could
pick up on this and prepare themselves
for an attack. This is possible as trees
have a host of chemicals they can use in
herbivore defense like bitter tasting
tannins or toxic alkaloids which have
been shown to be effective tools in
fending off pests. And scientists could
be pretty sure that it was VOCC's that
were inducing these responses since any
efforts to block airborne signals by
putting the tree branches in airtight
bags meant that neighboring trees took
more damage from the herbivores.
But hang on because there's a danger
here of entering into the same minefield
as the woodwide web drama. This behavior
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 neighbors whilst
it was being attacked by herbivores?
Wouldn't it be better for that tree if
its neighbors 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 neighbors, but the neighbors
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 VOCC's 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.
Tarpen are a specific group within the
VOCC's 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 elmleaf beetle with the
help of tarpen. See, the elmleaf beetle
likes to lay its eggs on the leaves of
the tree, ready for the larae to feast
on them when they hatch. But the elm has
some tricks up its sleeve to combat
this. They release turppines, which seem
to attract another insect, the euphilid
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 turppen 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 stop them from being able
to make tarpen.
They then collected all the odor
produced by the trees during this ordeal
and presented them to the wasps to see
what they do. As the team suspected, the
wasps spent significantly more time in
the test field when the tree odors
included turppins than when tarpin
production had been cut off.
With these results, the authors
concluded that it is the turppins that
attract the wasps and that the trees are
far more skilled at fending off beetle
attacks than we may give them credit
for.
So, as it turns out, trees have some
amazing ways of interacting with the
world around them.
Like any living thing on Earth, trees
can sense changes to their surroundings
and have employed suites of molecules
that help them to respond, whether it's
seeking out food, preventing attacks, or
calling out for help. So, yeah, trees
are amazing, but just maybe not in the
way we thought. And if nothing else, the
push back on the woodwide web should
motivate us to understand trees better,
as there are still so many fascinating
answers to be found.
I'll be honest, I originally expected to
tell a more traditional story of the
woodwide web, exploring a forest of
trees that are all for one and one for
all, assisting each other with their
intricate network of fungal friends. But
thanks to this new research, that is
definitely not how the story unfolded.
But I hope you'll agree that this is
still a tale worth telling. Though they
strive to be, scientists are not always
right. Ideas can and should be
questioned, details revised, and
corrections made as their research
unfolds.
Science is built on debate and
continuous pursuit of knowledge and
truth. no matter how long it takes to
find what that truth is.
Sadly, the woodwide web may be one of
those cases where our heads would turn
before the real truth came out. I hope
this video can go some of the way
towards setting the record straight and
show that the world of popular science
isn't always as infallible as it may
seem. And who knows, maybe next week the
world will be captivated by a new
narrative with an equally catchy name.
But by then hopefully we'll have learned
from the woodwide web and we can start
looking more closely at the results and
where they come from before we start
signing book deals and making calls to
Hollywood. So let's stay curious, look a
little closer, and keep giving the trees
the attention they've always deserved.
There is so much they can do, and they
are a huge part of what makes our planet
such a wonderful, thriving place to call
home.