Hey smart people, Joe here. Beneath your feet there is a secret network. This network trades resources, transmits information,
and can even go to war. I know what you’re thinking, and no, this
isn’t the world wide web.

It’s something much older. 450 million years older. And it makes life on Earth as we know it possible. This is the wood wide web. The most important social network on Earth. [MUSIC] Walk into a forest and just listen.

(forest noises) You can’t hear it, but the forest is communicating. If you’ve never noticed this before it’s
because all of this is happening below your feet. The wood wide web is a network created by
fungi.

They’re called mycorrhizal fungi and these
fungi live in and around the roots of trees and other plants. Fungi are a huge domain on the tree of life,
and as you’ve probably noticed by now, nobody knows how you’re supposed to actually say
it.

I’m going with “fun guy” because that’s
what I am. Fungi include molds, mushrooms and yeasts,
and as a whole they are essential to making all of Earth’s organic garbage and dead
stuff decompose and disappear.

While some fungi do resemble plants, they
are definitely not plants. They’re technically more closely related
to animals… but really fungi are a form of life like no other. Fungi don’t fossilize well so it’s hard
to know exactly when they first appeared in the evolutionary scene, but some fossil records
show mycorrhizal fungi have been living in this partnership since the first land plants
appeared in the Paleozoic, around 400 million years ago.

These underground fungi are essential to plant
survival. They also extend hair-like filaments called
hyphae into the soil which pump water even more efficiently than the tree’s own roots. Just like we need our vitamins and minerals
to grow, so do trees.

Plants from rose bushes to towering redwoods
need these micronutrients to survive! And mycorrhizal fungi are efficient little
miners. They use acid to bore holes into rocks and
fish out nitrogen and phosphorous.

In exchange for all this subterranean service,
a tree provides the mycorrhizal fungi with sugar, created through photosynthesis. Trees release between 20-80% of the glucose
they create to their fungal partners.

And older trees, the grandpop-lars and grandma-ples,
have more complex fungal interconnections than younger trees. But these mycorrhizal fungi do more than trade
minerals, water and sugar with their host tree.

They also form massive branching networks
of the fungal threads, called mycelium, that can extend thousands of acres, connecting
entire forests. If you dig into the forest dirt, you may see
these thousands of tiny white tubes if you look closely.

In a single pinch of dirt these hyphae, when
lined up, can extend 11 km! And these networks act as fungal freeways
for shipping chemical currencies. The fungi can act like a seasonal bank account
for trees, giving loans of sugar if the trees need an extra boost.

Scientists have found that if a tree is dying,
it will release its extra glucose into the wood wide web where it can delivered to younger
nearby trees, even trees of a different species. Trees can also use the network to send out
warning signals.

If insects bite into one tree, it can send
a chemical signal through the wood wide web, and when trees deeper in the forest receive
this insect alert message, they produce bitter compounds that make their leaves less tasty
to those same insects.

"The Ents are going to war!" Some trees, like black walnuts, even use the
network to spread chemical attacks, sabotaging other trees that try to grow too close. Across the globe, there are two main types
of these mycorrhizal fungi that make up the wood wide web.

Trees in cooler climates tend to host one
type, which create huge interconnected networks that cover massive areas. But warmer, tropical forests tend to be dominated
by a different type, which create smaller, more localized networks.

It’s like the difference between big, national
chain stores and your local farmers’ market. The balance between these two types of wood
wide webs is important to Earth’s climate. In general, the massive interconnected forest
fungal webs tend to lock up carbon in the soil as they decompose stuff.

And the more local network fungi tend to release
more carbon dioxide into the atmosphere. As global temperatures warm up, forests are
changing, and the balance of these two types of fungal networks is changing too.

More of the planet covered with tropical forests
means those large, carbon-storing fungal networks will be replaced by the more localized fungal
networks which release carbon into the air, which will just accelerate climate change,
which, even though plants eat CO2, is still not good.

So next time you’re walking through a forest,
take a moment to think about the very small but also very large network that exists under
your feet. Just because you can’t log on to the wood
wide web, doesn’t mean you aren’t connected.

It’s time we think of forests as more than
trees. Stay curious.

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