[bouncy upbeat music] (narrator) It looks like the latest forest relaxation fad, but this is no vacation.

It's actually the front lines of a battle.

These guardians have spent the past year in this forest fighting to protect a rare habitat from imminent destruction.

And the fate of an ancient community, whose importance we are just beginning to appreciate, hangs in the balance.

[bouncy upbeat music] In the old growth rainforests of the Pacific Northwest, giants dwell.

These ancients are among the tallest trees in the world and can live over 1,000 years.

Forests, like this, are home to a rich diversity of species, many of which are found nowhere else in the world, and they store about twice as much carbon per acre as the Amazon.

These temperate rainforests once stretched from Northern California to Southeast Alaska, but today, little remains.

In the province of British Columbia, Canada, more than 97% of the old growth forests with tall trees have been lost to logging, and the losses are similar in the U.S. One of the last intact valleys of primeval temperate rainforest outside of a protected area is here on Vancouver Island.

[bouncy upbeat music] The Ferry Creek Watershed lies within First Nation territory and is home to ancient cedar, spruce and hemlock trees.

(Bill) It also happens to be important spiritual area, cleansing places where we find balance and equilibrium in our lives.

(narrator) But big trees, like these, are also prized by industry because of the quality of the wood they produce.

Logging a place like Ferry Creek could generate millions of dollars in revenue for a company.

Because of that, this area has become a target.

Just a few kilometers away from Ferry Creek lies this solitary 1,200-year-old Douglas fir.

It's the second tallest such fir in all of Canada and once stood in a forest of ancient trees.

It's now a symbol of old growth destruction and has been given the name Big Lonely Doug.

And now the same company which clear cut this valley has been moving ahead with plans to log Ferry Creek.

[protestors singing in foreign language] But protestors from around the world have come to this forest, and they've joined up with some members of the Pacheedaht First Nation, within whose territory Ferry Creek lies.

For the past year, they've encamped around this valley and struggled to keep logging at bay.

(speaker) It just doesn't make sense why they can't preserve these huge ginormous trees when it's the last little bit of them ever in the world.

They've gotten all of the rest of it.

Why can't they just, like, leave these ones alone?

(speaker) It's really nuts we have to do this.

Like, look, this is crazy.

I'm no, like--I'm just, like, a mom and a surfer and, like, a regular person.

I'm not some sort of nutty, outdoorsy, extreme person, but this is what it takes for a change.

This is what it takes.

(narrator) But how does a small band of people stand up to a massive industry?

To protect these trees, you have to occupy them.

They build elaborate structures high up in the canopy.

Tree sitters might spend a week or more up here before they're forcibly removed.

(Shawna) I'm a bit emotional.

It's been, like, a couple super hard days.

Sometimes, I feel like how come everybody isn't here?

But I understand, that's the way this system is set up for us, you know?

We have to work so hard and keep our heads down and just keep going 'cause if we drop the ball, we'll lose it all.

There's people who have jobs that they really can't leave, but they know they just have to be here.

Like, we're just all doing this because we love it.

(narrator) Sitting in a tree prevents loggers from cutting the encircling forest.

They also build elaborate road blockades that prevent heavy equipment from entering.

[soft music] As the logging company, Teal Jones, has pressed its legal claim to cut these forests, police have arrested hundreds of protestors.

Some face significant financial penalties.

[drumming] They're taking these personal risks to protect the trees, but by doing so, they're also protecting a vast hidden network.

These trees share nutrients and water with each other by means of a sprawling labyrinth of underground fungi.

These microrisal fungi connect to the roots of trees and allow them to communicate with their neighbors about environmental changes and dangers, like hungry insects.

It's been dubbed the Wood Wide Web because of its striking resemblance to our human network.

And it means these trees are social beings.

Over 90% of the world's plant species form relationships with beneficial fungi.

But when forests are clear cut, these symbiotic relationships die with them.

Until recently, these complex networks in the soils were unknown and the forest floor may not be the only place these surprising connections occur.

These treetops play host to a vibrant, but little seen world.

They are biodiversity hotspots and havens for plants, invertebrates, and endangered species, like the marbled murrelet.

[metal clicks] [metal jingling] (Korena) When I first got the opportunity to climb up into a big leaf maple, I saw that there were so many plant species and just a habitat for other organisms to thrive high above the forest floor.

I was just in awe.

(narrator) Korena Mafune studies canopy soil, the thick brown mats of organic matter that collect in the canopies of old growth trees and which resemble soils found on the forest floor.

These soils are created by microbes and insects breaking down the leaves and other organic matter that collect on limbs.

It can take decades or perhaps even a century or more for these soils to accumulate and form.

Little is known about them or what function they play in the forest.

When Mafune started investigating them, she found something puzzling.

(Korena) Here I am up in a tree with these beautiful organic mats of canopy soil, and there's roots in this canopy soil.

It was astonishing.

(narrator) Why would a tree spend precious energy growing roots out of its limbs high above the forest floor?

(Korena) I was like, "If there's roots up there, they have to be doing something for these host trees."

One of the things I started noticing is that there was mushrooms growing up in this canopy soil environment.

(narrator) Not only were fungi connecting with the trees' root systems in the canopy and exchanging resources, the soils themselves were rich with the essential nutrients.

In fact, there's vastly more nutrients per kilogram of canopy soil than per kilogram of forest floor soil.

(Korena) I think that during certain times of the year, these host trees may actually be depending on the resources and the plant fungal partnerships in their canopy soil environment to help them survive.

(narrator) These canopy soils are found in old growth forests around the globe.

And if Mafune is right, these canopy soils and their fungal partnerships could be a key to the resilience of old growth forests, allowing trees to survive for hundreds of years through droughts and other stressors.

Even when we replant the forests we cut, it takes decades to centuries for these complex ecosystems we see in old growth to reestablish themselves, thus making the trees less resilient at the very time they need it the most.

Scientists like Mafune are only just beginning to unlock the mysteries of these ancient forests, and as more of them disappear, what secrets are we losing?

(Korena) We don't only lose those trees, we lose an ecosystem that provides habitat to endangered species, to species that have never even been discovered.

These forests, they just hold such a special place in my heart.

They are way more than a research project.

(speaker) Listen to your heart 'cause it will tell you what the right thing to do is.

[gentle upbeat music] Accessibility provided by the U.S. Department of Education.

[gentle upbeat music continues]