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.