Hey, smart people.

Joe here.

Beneath your feet, there is a secret network.

This network trades resources, transmits information, and it can even go to war.

I know what you're thinking.

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.

OK, walk into a forest, and just listen.

You can't hear it, but the forest is communicating.

And 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 mycorrihizal fungi.

And these fungi live in and around the roots of trees and other plants.

Now, fungi are a huge domain on the tree of life.

And as you probably noticed by now, nobody knows exactly how you're supposed to say it.

But I'm going to go with "fun-guy", because that's what I am.

Fungi include molds, mushrooms, and yeasts.

And as a whole, they're 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 are 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 mycorrihizal 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 mycorrihizal fungi are efficient little minders.

They use acid to bore holes into rocks and fish out nitrogen and phosphorus.

In exchange for all of this subterranean service, a tree provides the mycorrihizal fungi with sugar created through photosynthesis.

Trees release between 20% and 80% of the glucose that they create to their fungal partners.

And older trees, like the grand poplars and grand maples, have more complex fungal interconnections than younger trees.

But these mycorrihizal 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 to 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 kilometers.

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.

And scientists have found that if a tree is dying, it will release its extra glucose into the Wood Wide Web where it can be 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 the same insects.

Some trees, like black walnuts, even use the network to spread chemical attacks, sabotaging other trees that try to grow too close.

And across the globe, there are two main types of these mycorrihizal 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 farmer's 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.