All language subtitles for NOVA.S52E08.Secrets.of.the.Forest.1080p.WEB.h264-BAE_track3_[eng]

♪ ♪

♪ ♪

NARRATOR:
There are more trees
in Earth's forests

than stars in our galaxy.

Could they be key to the quest
to cool our planet?

LOLA FATOYINBO:
All of these plants

are taking up the CO2
that's in the atmosphere.

NARRATOR:
How much carbon
can forests soak up?

And what would we need to do
to maximize this effect?

To answer these questions,

scientists are on a mission
to decode

the secrets of our forests...

TOM CROWTHER:
You can feel

the presence of everything
that is needed to keep us alive.

NARRATOR:
...investigating how complex
forest ecosystems work...

REBECCA COLE:
The more diversity
that you have,

the more diversity can exist.

NARRATOR:
...examining the role
of everything

from fungi hidden
beneath our feet...

TOBY KIERS:
This is live.

We're watching the fungi
move nutrients right now.

NARRATOR:
...to the bugs, birds,
and even humans...

MAURO GALETTI:
Every plant, every animal
has a different role

in the whole ecosystem.

NARRATOR:
...calculating how they can all

interact to help cool
a warming planet.

"Secrets of the Forest,"
right now, on "NOVA."

♪ ♪

(birds chirping)

NARRATOR:
Within every forest
is a story with many threads.

♪ ♪

The overstory.

The understory.

A story of such intricacy,

it challenges the greatest minds
with its complexity.

As scientists learn more about
the extraordinary chemistry

of these ecosystems, they're
asking a provocative question:

Could forests offer a natural
way to help cool our planet

by removing carbon
from the atmosphere?

♪ ♪

CROWTHER:
I would be surprised
to find anyone

who doesn't feel more at peace
in a forest like this.

You can feel

the presence of everything
that is needed to keep us alive.

♪ ♪

NARRATOR:
Tom Crowther is an ecologist
based in Switzerland

who believes that
healthy forests hold the key

to keeping our planet
from overheating.

CROWTHER:
This is what distributes

the nutrients throughout
the entire forest.

This is a saprotrophic
cord-forming

basidiomycete fungus.

My God.

It's a salamander.

(chuckling):
So beautiful.

♪ ♪

I mean, this is...

...a natural forest,

with all the healthy mixture
of species that you need

to support
the immense abundance of life,

but also, importantly,
to lock away lots of carbon.

NARRATOR:
Tom is trying to figure out
the potential of forests

to absorb carbon
from the atmosphere

through photosynthesis.

This chemical reaction

enables a tree to build
its solid structures

from little more
than air and water.

Inside every leaf,
special parts of the cells

take carbon dioxide molecules
from the air

and combine them
with hydrogen from water

to create sugars
that will be used to build wood.

This astonishing process is
powered by light from the sun.

And that transfer of carbon
from the air

happens in every single tree
on the planet.

At NASA's
Goddard Space Flight Center,

Lola Fatoyinbo uses satellite
data to monitor the effect

that trees and plants have

on the carbon dioxide
in our atmosphere.

Everything that you're seeing
here in the red and orange tones

is CO2 moving across our planet.

You can really see
how they're swirling around,

moving almost like a river.

You also see that it's not
distributed evenly.

Most of it is actually in the
Northern Hemisphere.

And this is because

most of the land masses

and most of the emissions come
from the Northern Hemisphere.

♪ ♪

As we get into
the spring months,

and you have trees greening,
you have grasses growing,

you have
photosynthesis happening.

All of these plants

are taking up the CO2
that's in the atmosphere,

and concentrations are going
way down.

You don't see all this red
anymore in the north

that we did before.

This is the system
that has been regulating

how much carbon dioxide
is in our atmosphere

for millions of years.

NARRATOR:
Biologists like Lola and Tom
want to harness

the natural power of forests
to help absorb carbon.

CROWTHER:
That's what these plants do.

They literally capture carbon
from the atmosphere

and they store it
for different periods of time

in their biomass
and in the soil below.

And that process
of carbon capture

is a ready-made tool in the
fight against climate change.

NARRATOR:
Tom estimates that,
over the course of history,

humans have felled almost half
of the world's forests.

So, could restoring lost forests

absorb enough carbon
to help slow climate change?

To find out, Tom and a team
built a computer model

to estimate the potential.

CROWTHER:
So we collect data
from all over the planet,

and that can show us

there's about 0.9 billion
hectares of land

outside of
urban and agricultural land

where forests might naturally
be able to regenerate.

That's a big chunk of land

that would be able to capture
a staggering amount of carbon.

NARRATOR:
Calculations suggested
that to capture this carbon,

there was enough land to support
an extra trillion trees,

a seductive idea that made
headlines around the world.

CROWTHER:
It just went viral beyond

anything I could
have been prepared for.

And I think that alliteration,

"trillion trees," was both
a blessing and a curse.

In one way, it captured
everyone's imagination.

"Great, we bring back
a trillion trees,

and we're gonna be flying."

But the downside was,

everybody thought
that meant planting trees.

Somehow, it, it wasn't
about the forest,

it was about the trees.

And that is where things
started to go wrong.

It nearly finished
all of our careers.

♪ ♪

Companies and governments
were under a lot of pressure

to limit their emissions.

They saw this as a chance

to just bang a load of trees
in the ground,

and then they don't need
to cut emissions.

There are projects announced,
as a result of our paper,

saying, "Don't worry,

we're gonna buy up land
and we're gonna plant trees."

NARRATOR:
In the rush to grow trees,

people ignored the supporting
environment that exists

in a forest.

As an ecologist and member of
the Citizen Potawatomi Nation,

Robin Wall Kimmerer
knows the importance

of biodiversity in a forest.

The interconnections
between species

have long been understood

by many Indigenous people
around the world.

There are places on the planet

where biodiversity

continues to thrive.

And those places are, by and
large, in Indigenous homelands.

Biodiversity is the sum total

of all of the organisms
that are here.

And you think,
"Well, why does it matter?"

In a forest
which is self-generating,

you get all
the different forms of trees

and the understory
and the mosses and the fungi

and the birds,
all in relationship.

It's this beautiful web
that doesn't really exist

in a monocultural plantation.

NARRATOR:
When Tom's paper was published,
many quite literally

couldn't see the forest
for the trees,

by planting rows of single tree
species to capture carbon,

instead of reducing
carbon emissions.

CROWTHER:
This greenwashing is one of
the most insidious threats

to climate change
and biodiversity.

And through this paper,
in some people's minds,

I had become synonymous
with greenwashing.

I still regret

how I handled that paper.

It's the
hardest thing to be hated

by people that you agree with.

(chuckles): I just stayed in the
flat

reading everything on social
media.

And it just, like...

Yeah, there's no response--
you...

You don't know...

I was just crippled.

I didn't know what to reply to
and what not.

I just wanted to say,
"I'm sorry," to everyone.

♪ ♪

There was a point where I was,
like, "Let's drop out of this.

I don't need this in my life
anymore."

But that was weighed up against

this absolute desperation
to show the world

how much carbon can be captured
with healthy biodiversity.

♪ ♪

NARRATOR:
Tom and his team decide
to set the record straight.

They begin building a new,
more accurate computer model

that shows the potential of the
whole forest to capture carbon.

Working with more than 200
scientists around the world,

they set out to estimate
how much carbon could be stored

in each part
of the forest ecosystem...

...starting with the trees.

♪ ♪

This is the Osa Peninsula
in Costa Rica,

home to one of
the world's last remaining

old-growth tropical forests.

Ecologist Rebecca Cole has
studied this forest for decades.

COLE:
There's no other rainforest
that I've been in

where the trees are
this tall and this magnificent.

Kind of like being
in a cathedral.

NARRATOR:
In old forests like this,

individual trees can survive
for hundreds of years

and can store
huge amounts of carbon.

We have a giant emergent tree.

It's probably
300, 400 years old.

Wood is about 50% carbon,

so there's a huge amount
of carbon

stored in a tree this size.

We have photosynthesis happening
up there, with the leaves,

and sending carbon,
in the form of sugars,

coming down through the stem
and out into the root system.

♪ ♪

NARRATOR:
Trees take carbon from the air

and move it through their bodies

inside living cells
that act as long, thin tubes.

These flows feed the tree,

using the carbon
to create the wood

of its trunk, branches,
and roots.

At the same time, water
and nutrients from the soil

are pulled upwards
through the tree.

When the water reaches
the leaves,

it's stored,

then used in photosynthesis
or released into the air.

The tree is essentially
breathing in carbon dioxide

and exhaling oxygen.

♪ ♪

By measuring individual trees,
researchers like Rebecca

can estimate how much carbon
is held in the trees

of a given area of forest.

Diverse forests, which support
older, bigger trees,

can hold nearly twice
as much carbon

as plantations of younger trees.

♪ ♪

In Zurich,
Tom and his student Lidong Mo

are using tree data
in their computer model

to estimate the potential

of the world's forests
to store carbon.

They break the planet down
into millions of pixels

and input data
from field scientists.

CROWTHER:
Each black dot
indicates a place

where someone has measured
biomass and carbon storage

in that location.

There's about 1.2 million
data points

where someone's
stood on the ground

evaluating the state
of that forest.

NARRATOR:
For areas without field data,

they use satellite imagery
and A.I. machine learning

to fill in the gaps.

But to fully estimate how much
carbon forests can capture,

they need to consider more
than just trees.

CROWTHER:
We need to include the fungi,
the bacteria, the animals,

and then start to predict
the global pattern.

(mouse clicking)

NARRATOR:
In forests,
carbon flows beyond the trees

into the entangled underworld
of fungi.

FRANCIS MARTIN:
I like the rain

because this is the time
of the mushrooms.

♪ ♪

NARRATOR:
Biologist Francis Martin

has studied forest fungi
for decades.

When mushrooms begin to emerge
in the fall,

he couldn't be happier.

MARTIN:
I really like walking
in the woods,

picking mushrooms,

because mushrooms are
very beautiful organisms.

Wow, it looks like, uh,

the porcini,
a very tasty mushroom.

A great mushroom.

This mushroom
is likely the death cap.

If you eat a piece
of that cap...

(clicks tongue):
...you are dead.

So, please avoid
to have that one for lunch.

Wow.

Magnificent.

The king of the forest.

The iconic mushroom.

The fly agaric.

If you peel the cap
of the fly agaric,

and if you dry it,

you smoke it
or you eat it,

and then it's full
of psychedelic compounds.

I should confess that
I never dare to taste it.

I should before I die.

I prefer burgundy wine
or, even better, Chablis.

What you see there is
only the tip of the iceberg,

only maybe five,
ten percents

of the mass
of the mushroom.

The, the real mushroom,

the most active part
of the mushroom,

is underground,

making, uh,
long hyphae,

long filaments
of cells

called the mycelium.

It's like, uh,
it's like a web, you know?

It's like a web
growing beneath our feet

and, and connecting
to the trees.

♪ ♪

NARRATOR:
A single handful of soil

can contain miles
of fungal threads

that form an intricate network.

Fungi are not plants.

They don't use photosynthesis
to grow.

But they do need carbon.

So fungi like this

have evolved
to connect to tree roots

and take carbon in the form
of sugars from the tree.

In return, the fungi give
minerals and water to the tree.

MARTIN:
The tree will provide sugars
to the network.

And this network
will use the sugars

to fruit and make
this beautiful mushroom.

NARRATOR:
Inside the gills
of the mushroom,

millions of tiny spores form.

These reproductive seeds
are carried away

by wind, rain, or insects

to begin new fungal networks
elsewhere in the forest.

I can feel the mycelium
beneath our feets,

are just crawling, full of life,

and, and trying to emerge-- wow.

♪ ♪

NARRATOR:
More than 80%
of all plant species

form partnerships
with the underground mycelium.

By providing
nutrients and water,

fungi support the growth
of the forest.

♪ ♪

In Amsterdam, a team of

biologists and physicists
is studying

how fungi and plants
exchange carbon and minerals.

They grow plant roots and fungi
in petri dishes

and examine their interactions
under a microscope.

LORETO OYARTE GALVEZ:
We take an image for every
petri plate every two hours

so that we can see how
the fungi's actually growing.

♪ ♪

NARRATOR:
The images show the fungi
growing hundreds of threads

that simultaneously search
for new sources of carbon.

These patterns are just
a few inches across.

Imagine the scale
of the networks

running through
an entire forest.

GALVEZ:
We can see the highways,
but we can also look

into the traffic
inside those highways.

WOMAN:
I can move to fluorescence.

♪ ♪

KIERS:
Wow-- this is live.

We're watching the fungi move
nutrients right now, right here.

And that gives us
a whole new way

of studying fungal behavior.

NARRATOR:
They're discovering

that in the partnerships
with plants and trees,

fungi are highly manipulative
power brokers.

KIERS:
The fungi

have evolved strategies

to be able to identify
the plants

that give them the most carbon

in return
for phosphorus and nitrogen.

They'll actually hoard it
in their network

until the price of that
phosphorus and nitrogen go up,

until the plant really needs it.

And then they'll get
more carbon in return.

Or they'll move it across

to a totally different part
of the network,

where the root is
giving more carbon in exchange

because it needs
more nitrogen and phosphorus.

And for hundreds of millions
of years,

these fungi have been
evolving strategies

to really maximize
their trade with plants.

♪ ♪

NARRATOR:
An estimated 3.5 billion
metric tons of carbon

moves from plants into
fungal networks every year.

And forests
with healthy fungi will

ultimately store more carbon

than plantations that lack them.

♪ ♪

Tom Crowther began his career
studying fungi,

examining how samples grow
and interact

in small dishes,
at Yale University.

When you put two fungi together
in a petri dish,

But when you add a third fungus,

quite often, it will fight
with the one that's winning,

so the other one can survive.

As you add a fourth and then
a fifth fungus to the system,

the more likely you are
to find stability

so that they all survive.

We call them microcosms,

but they are microcosms
of the real world.

They're a, a glimpse
into what's happening in nature.

Diversity begets diversity.

NARRATOR:
Tom was captivated
by this balance he saw

when lots of species
live in close proximity.

His findings on fungal
interactions were good science,

but the focus of his work
was narrow.

CROWTHER:
I was definitely too scared
to step outside of my field.

And I was... You know,

it's, it's safer
to stay in your petri dish.

NARRATOR:
Then, one day, something changed
Tom's outlook on the world.

CROWTHER:
So I'm a postdoc in Yale,

and my friends come over
for a holiday,

and we jumped off this rock.

It's pretty high.

And as I entered the water, my
face got slapped by the water.

And I just climbed onto the boat
and immediately went to sleep.

And then for the next few days,
I was just weird.

I was just, like,
walking into walls

and, and just knocking over
tables.

And the doctor did the CT scan,

and I was waiting in, in his
office for him to come back,

and he just came in
holding a neck brace,

and he just went, "Right,
stay still, don't move at all,"

put it around my neck,
and was, like,

"The ambulance is coming.

You've had
a very serious stroke."

There was a hole in my brain.

I went into a pretty serious
depression, and it was just...

...a, a long, long,
dark journey after that.
(chuckles)

The stroke was bad--
the depression was way worse.

♪ ♪

I'd always loved
my petri dishes,

but I'd always dreamed of going
bigger, but I was too scared.

Suddenly, after this period,

with the stroke
and the depression,

that was no longer a real fear.

You've only got one life,
you may as well go for it.

NARRATOR:
Emboldened by his stroke,

within six months,

Tom's petri dish
became the entire planet.

Now he sought the answer
to a simple but big question:

How many trees are there
on Earth?

So, along with his Yale
roommate, Greg Hintler,

he began to gather information.

We started asking people,
ecologists around the world,

"How many trees are
in your patch of forest?"

And once we had enough data,

we could start to see,
like, a global perspective.

We were pretty astonished
to find

that we're not talking
about millions or billions.

There was actually three
trillion trees on the planet.

And that blew our minds.

It was, you know,
this first glimpse into

the immense scale
of this system.

NARRATOR:
Tom's big data approach
to ecology

had revealed that there are
many times more trees on Earth

than stars in our galaxy.

Trees are important
carbon capture machines.

But there's another part
of the forest

that plays a critical role.

And Tom is eager
to track its power.

♪ ♪

(birds chirping and calling)

Writer and environmentalist
George Monbiot

believes that the soil

is the most underappreciated
part of the forest ecosystem.

MONBIOT:
Right, let's see
what we can see under here.

♪ ♪

What's that?
That's a root.

♪ ♪

This is perhaps the most
important of all animals.

It's an earthworm.

But if you really
want to insult someone,

you call them a worm.

(chuckling): Right? It's...

It's the most terrible insult
to worms,

because of the tremendous work
that worms do

in terms of building soil
and maintaining its fertility.

♪ ♪

Soil is a biological structure.

It's built by the organisms
that live in it,

just like a coral reef.

And most of the organic carbon
in the soil

takes the form of the glue
used by creatures

to stick the soil together.

This is a baby earwig.

Might not look like
very much,

but this is one of the giants
of the soil.

This is like an elephant
or a rhino or a hippo,

because the great majority
of what you find

is really, really tiny.

There's a centipede here.

There we go.

And this is one of
the big predators of the soil.

Look how fast it moves there.

Ooh-- they're like
lions or tigers.

(chuckles)

I love soil.
(laughs)

You might have guessed.

NARRATOR:
More than half of all
the species on Earth

are thought to live
in the soil.

A little fly larva.

NARRATOR:
Most are too small to see
with the naked eye.

But powerful microscopes
reveal the diversity

of these remarkable creatures.

♪ ♪

At the smallest scales,
microorganisms like bacteria

exist in close partnership
with trees and plants.

One of the most amazing
revelations in any science

in the past few years

is that plants can talk.

And plants can talk in, in a
very rich and complex language.

It's a chemical language.

And what happens in the spring,

when roots are pushing
through the soil,

the little root hairs
are growing,

is that they will release
very, very complex chemicals

whose purpose is to speak
to just one or two

of the hundreds of thousands
of species of microbes

which might be
in that region of soil.

Most of those microbes
won't necessarily

do the plant any good,

some are positively harmful,

but some are extremely
beneficial.

And it's those ones
they want to wake up.

The plant floods those bacteria
with sugar,

and amazingly,
between ten and 40%

of all the sugars that plants
make through photosynthesis

is poured into the soil.

And at first sight,
it looks like

pouring money down the drain.

They go to this massive effort
to make all this sugar

out of sunlight
and carbon dioxide and water,

and then they go
and dump it in the soil?

What's going on?
They're feeding the microbes.

♪ ♪

NARRATOR:
In the soil around their roots,

trees and plants
cultivate microbes

to break down
the minerals they need

and to fight off
harmful bacteria.

Just as we rely on microbes
in our guts to digest our food,

plants also need
a healthy microbiome--

the rhizosphere
that surrounds their roots.

The rhizosphere
might lie outside the plant,

but it's the plant's
external gut.

And to make this comparison
even spookier,

of the thousand or so
phyla of bacteria,

the major groups,

there are four that dominate
in the rhizosphere,

and there are four that dominate

in the human gut.

And they're the same four.

♪ ♪

CROWTHER:
There's soil ecologists

in every location
you can ever think of.

And by pulling together
that data,

we get a picture

of the soil carbon storage,
and then that

we use to scale
those forest estimates.

NARRATOR:
Tom's model predicts

that an extra
45 billion tons of carbon

could be stored
in dead wood and leaf litter

and an additional
nearly 35 billion tons

in the soil itself.

But the soil's microscopic
creatures

are not the only animals

that shape the flow of carbon
through the forest.

To maintain
a balanced ecosystem,

a healthy forest needs insects.

In Bouddi National Park
in Southeast Australia,

Tanya Latty is sweeping
the forest for bugs.

♪ ♪

LATTY (whispering):
Oh, she's so pretty.

This is a praying mantis,
and she's an ambush predator.

So she waits till she sees
some food nearby,

and then she'll just

reach out
with those two big front legs

to capture her prey.

(gasps)

Jumping spiders
are also predators,

so they'll eat anything
they can jump on

that's smaller than themselves,

and they have
some of the best vision.

♪ ♪

Grasshoppers are herbivores,
so they eat plant material.

But they're really important
as a source

of protein and fats,
for many of the animals

in this forest will eat
a big insect like this.

Oop!

(laughing):
He landed on the net.

NARRATOR:
Animals like

mantises
and spiders

eat smaller insects
that, if left unchecked,

could damage trees and plants
in the forest.

In turn,

these larger bugs feed birds

and small mammals
that help spread seeds

and support the forest
in other ways.

LATTY:
70% of all animal species
are actually insects,

so they are the vast majority
of biodiversity.

Insects are
our primary pollinators.

They are our pest control.

They're important

for recycling matter
back into the ground.

A forest like this one
could not exist without insects.

♪ ♪

NARRATOR:
In the tree canopy,

larger creatures play
an important role, too.

♪ ♪

(insects and birds chittering)

In the Atlantic Forest
of Brazil,

ecologist Mauro Galetti
is on the trail of muriquis.

♪ ♪

Muriquis are one of the largest
primates in the Americas.

But they're also
one of the most endangered.

They're rarely seen.

♪ ♪

(animals chirping and calling)

Call of the muriqui.

Amazing.

There, you hear?

You see?
They are here.

You see? A muriqui in among,

crossing here.

There, over there.

Wow.

Wow, you see?
Different individuals--

adults, females,

juveniles.

(chuckling):
It's not every day

that you see muriquis
like this, so close.

They're super-rare,

and their populations
are very small.

They only occur here.

Nowhere else in the world--
another one there.

You see?
Yeah, that's a baby.

(object drops)

They're pooping on us.

(laughs)

So when they wake up,
they poop,

and they disperse
a lot of seeds.

And then they move to
another tree and another tree,

and then they're, you know,
keep doing their job.

That's planting the forest.

♪ ♪

NARRATOR:
Animals like muriqui

are essential for the survival

of large trees in the forest...

♪ ♪

...as here in the tropics,

trees need animals
to spread their seeds.

GALETTI:
This is a tree
that is fruiting now.

It's a large tree,

and when it's fruiting,
all the, all will drop.

And you can see
the fruits here.

And open--
you see?

(chuckles):
They're dropping.

Insects or fungi or rodents

come to congregate here

to eat the seeds that's inside

this juicy pulp here.

And these seeds,

they have to compete
with the mother plant

for nutrients and light.

So they won't germinate.

What the plant really needs
is someone

to swallow the whole thing

and take away,

and plant somewhere else,

not close to the parent tree.

♪ ♪

NARRATOR:
The animals are the gardeners
of the forest.

Mauro's research has shown
that in this forest,

90% of the trees rely on animals

to move their seeds
in order to reproduce.

The largest trees
that store the most carbon

typically have the biggest seeds

and need animals like muriqui
to disperse them.

♪ ♪

GALETTI:
Whoo-hoo!

Look what we have here.
(chuckles)

Muriqui poop.
(laughs)

It is fresh and full of seeds.

Can you see all the seeds here?

Oh, look at this big seed
here.

Wow, there's one that is
really big.

You see?
So this big seed

will make a big tree,
which store more carbon.

Like you have here.

There's one
particular example.

So you have the muriqui poop,
the seed,

and you have the seedling.

You never imagine
that could become

a giant tree
that store a lot of carbon.

♪ ♪

This is the future
of the forest.

♪ ♪

NARRATOR:
The absence of just one
animal group, like birds,

can reduce the potential
of forests to store carbon

by around 38%.

As forests decrease in size,

these species are disappearing.

And that's due to another animal

that's had more influence
in the shaping

of modern forests
than any other.

♪ ♪

In the highlands
of Southern Costa Rica,

Rebecca Cole witnessed

the dramatic loss
of old-growth forests.

As a young girl,
she saw her parents

clear the forest for farmland.

COLE:
What happened in this landscape

was, when my parents came in,
it was a frontier.

It was upwards
of 90% forest cover.

People thought that nature
was sort of endless.

It was an endless resource, and,

you know, learned
that it's very finite.

People started
clearing the land.

It's very steep,
it rains a lot here.

All of the nutrients are
in the vegetation.

When you cut it down,
it just very quickly leaves

very impoverished soil
behind.

So the land became degraded
very quickly

and was very difficult to do
any sort of agriculture on.

Got into restoration ecology
to try to,

to bring back the forest...

(voice trembling):
...because my parents were
some of the people that

chopped it down.

♪ ♪

My dad's trajectory was

coming in and thinking that
we were going to conquer nature.

He wrote up a whole book
that was essentially

an apology.
(chuckles)

♪ ♪

NARRATOR:
Rebecca is now trying
to restore forests

in areas cleared by her parents.

In some fields,

it's virtually impossible
for trees to grow again

without a helping hand.

COLE:
This is one of these
introduced pasture grasses

that just takes over, uh,
big areas

and doesn't let much else grow.

And they're
just very aggressive.

You just don't get
any natural regeneration

in areas that are covered
with this type of grass.

We go deeper into the weeds.

NARRATOR:
To give trees a fighting chance,

Rebecca plants islands
of hardy species like guaba

amidst the sea of grasses.

This is one of my favorite
species for restoration,

Once it gets up above the grass,
it just sends its branches out.

It creates a lot of shade,
drops a lot of leaf litter,

and it creates a wonderful,
safe site

for seedlings to grow.

This little seedling
is a couple of years old.

We've got a couple other ones
around us that are

just starting to poke out
over the top of the grass.

Birds will see this
as a perching structure

and they'll perch.

Hopefully they'll poop,
they'll leave seeds here,

and those seeds will have

a better chance
of germinating and growing

than they will out
in that ocean of grass.

Vi más antes
cuando habían flores.

NARRATOR:
The research team charts
the progress

as the tree islands
expand outwards.

♪ ♪

They monitor the birds and bats
that visit

and collect samples

of the tree seeds
that are dropped.

By identifying individual seeds,

the team can find out
which tree species

are spreading well
and which are struggling.

The goal is to figure out

the best methods
to speed forest regeneration

in degraded areas
across the tropics.

Planting small islands
of the right trees

could help create the
ancient forests of the future

without the need
for mass tree planting.

But finding suitable land

for large-scale
forest restoration

that doesn't destroy
people's livelihoods

can be a challenge.

Tom and Lidong exclude
current farmland

and urban areas
from their model.

Their main focus is
on the potential

of existing forests
and land outside of human use.

CROWTHER:
In between them,
it looks...

NARRATOR:
They are almost ready

to publish their study.

I mean,
it's looking good.

I think we, after
four years

of eternally adapting
these models,

I think, I think I'm feeling
pretty confident.

Five years.
Five years, so...
(chuckles)

More than five years.

Yeah, fair enough.
(laughs)

Five years,
ten million models,

and hundreds
of co-authors later,

I think we've got it.

I think we're
looking pretty good.

♪ ♪

NARRATOR:
As the publication date
approaches,

Tom prepares to face the media,

hoping to avoid
another backlash.

In an online press conference,

he announces how much carbon
their model predicts

forests could store.

So, yeah, thank you all
for joining.

For a little bit of
background information,

for the last few, few years,
a large network of ecologists

have been trying
to build this integrated

global forest assessment
by working together.

The average effect
across all of those models

is around
226 gigatons of carbon.

NARRATOR:
The average forest today

is only around 30%
of its full maturity

because we've stripped out trees

and damaged
the underlying ecosystem.

So, most of the potential

lies in restoring existing
forest to full health,

and the rest
by regrowing lost forests.

The team estimates that
226 billion tons of carbon

could be captured--

almost a third of
all the carbon emitted

since the Industrial Revolution.

But forests won't
help fix our climate

unless we also dramatically
cut our emissions.

CROWTHER:
That is a really exciting
opportunity

to achieve massive-scale
carbon capture

simply by protecting
the ecosystems that we have.

There cannot be a choice

between nature
and decarbonizing.

We absolutely must take steps

to achieving both
simultaneously.

(traffic humming in distance)

♪ ♪

NARRATOR:
Now Tom wants to get
the message to world leaders.

At the United Nations
climate meeting in Dubai,

he seizes the opportunity
to address them

on the biggest of stages--
at the COP summit.

Thank you so much.

The link between nature
and climate is so critical.

The conservation
of existing forests

is our most powerful carbon
drawdown tool,

allowing those ecosystems to
regenerate.

Then, on top of that,

the recovery
of diverse ecosystems

in degraded landscapes
can achieve the remainder.

This cannot be achieved, though,
through mass plantations,

because the power of nature
is in its complexity.

Which means that diverse forests

store more than twice
as much carbon

as monoculture plantations
would.

And we cannot be achieving this
without emissions cuts.

There can be no choice between
cutting emissions and nature,

because we categorically
need both.

It's only when nature and people
thrive together

that we will have long-term
carbon capture as a by-product.

(audience applauding)

Thank you very much.

(applause fades)

NARRATOR:
Tom's message to preserve
old forests is being heard.

But what is
their current health?

NASA collects data
from sites on the ground.

FATOYINBO:
These are billions
of laser points

that were collected in the field

with an instrument called
the terrestrial laser scanner

to essentially make
really detailed measurements

of forest composition
and forest structure.

NARRATOR:
Measurements like this
support Tom's findings

that we need to preserve
old-growth forests

because they store more carbon
than plantations.

But satellite imagery shows

we're losing ancient forests.

Over 15,000 square miles
is felled each year,

mainly for cattle grazing
and crop growing.

♪ ♪

So, what's the answer?

Can we still have
the things we need,

like food and timber,

while restoring
the planet's ancient forests?

(sirens wailing in distance)

KIMMERER:
Many of us live today
in cities,

which, in terms
of ecological footprint,

can be a really good thing.

But that does mean that we feel
disconnected.

We don't see the way that our
food

is coming from the land.

It becomes invisible to us.

♪ ♪

NARRATOR:
Robin Wall Kimmerer believes

that Indigenous practices show

that you can take from nature

without damaging the ecosystem.

KIMMERER:
In Potawatomi ways
of thinking,

we're always said,
"Well, how do I give back

in return
for what I've been given?"

We have a worldview that says

that the forests
are our relatives,

they are our providers,

they take care of us,

and we have
to take care of them.

But we also need wood
for our homes,

and we need firewood,
and we need berries, and...

So the ethic is not
that you don't take,

because we have to take.

Only take what you need.

Be in reciprocity, give back
for what you've taken.

Use a technology

which minimizes harm.

Whether we're taking it directly
from a forest

or whether we're going
to the corner store,

it's still all coming
from the Earth.

♪ ♪

NARRATOR:
Tom's research offers

a practical way to help
people connect with forests.

Anyone can access
his online maps

to check an area's
natural potential.

(mouse clicking)

CROWTHER:
You can now zoom
around the world.

You can draw
around that location

and automatically gain insights.

We can see
about the carbon storage

that's being generated
in all those ecosystems.

And what's really cool,

we've had hundreds of thousands
of local farmers,

Indigenous communities,
local populations

drawing around their areas
on the map,

and they get
ecological information,

but they then
also gain visibility.

So now we can all see them.

One of the examples
I often use--

Where is it? It's in Ethiopia--

is Desta's farm.

You can see,

from the surrounding area,

there's a massive
agricultural footprint

of coffee production,

but as we zoom in to Desta's,

we can see it's an absolutely
intact rainforest.

And that's because he's
planting the coffee trees

underneath the canopy,

which is trapping
water and nutrients

and supporting those trees,
so they grow well.

♪ ♪

And with tools like this,

you can now start to see

where you're getting
your coffee from.

You can identify

the footprint that
it's having on biodiversity

and carbon and water,

and that means
you have the power

to then choose
a positive product

rather than a negative one.

So with every little decision,

you and I
are changing the world.

We're all contributing
to global restoration.

♪ ♪

♪ ♪

This is the place
I come every weekend.

(chuckling):
I, I feel like my social life

has been replaced by forest.

(fire crackling)

♪ ♪

Five years ago, it was,
no one mentioned nature

when it comes to climate change.

Four years ago,
everyone was just

pledging how many trees
they can plant.

Now everyone's committing
to how much

Indigenous land
they can protect,

or how many rights of farmers
that they can empower.

It's unbelievable.

It feels like momentum
is now building.

♪ ♪

GALETTI:
We don't know anything
about the forest.

We're just starting.

There is a lot of pessimism--

climate change, biodiverse
loss--

but I think never ever in human
history,

in saving animals,

saving plants,

doing ecology.

COLE:
I lose a lot of sleep over

the challenges
that we're facing,

but it's so much easier
to do something about it

than it is to do nothing.

And hopefully,
that'll make a difference.

MARTIN:
There's a huge number
of species

which remain unknown,

hundred of species

which are very critical
for the life of planet Earth.

These need to, to be active

to support the life--

the trees, the plants,

and probably mankind.

♪ ♪

KIERS:
We're in a whole new era
of science right now.

I get goosebumps just thinking
about it.

We used to categorize things,

but now we're in an era

that studies interactions.

It's not going to be
about just one solution,

like planting trees.

It's going to be
about understanding

the interactions
between all organisms

in an ecosystem,

and saving those interactions.

♪ ♪

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