♪♪ ♪♪ -Orcas.

They live together in close-knit families.

Some pods stay in the same area for generations, like this one off the northwest coast of America.

♪♪ In 2018, they hit the headlines.

-A mother orca whose calf died after birth is still carrying her baby 17 days later.

Watching this mother orca express a very human emotion, this outpouring of grief -- some are calling it a "tour of grief."

Researchers say that they're now concerned for the mother's health.

-She's not the only mother in difficulty.

70% of females are miscarrying their babies.

The future of the whole community is under threat.

The race is on to save them.

-Yeah, there's -- oh, he's right there.

-These orcas are the most studied population on the planet.

And researchers now realize their future depends on a completely different environment.

♪♪ -If humans get our acts together and start thinking about the whole ecosystem, we're going to be recovering the whales, and ultimately, we're going to be saving ourselves.

-Across the world, people are studying ecosystems and looking for connections, giving us a deeper understanding of nature.

♪♪ We're at a turning point in history and moving in a new direction.

How we live with nature now will determine our future.

A new age is upon us -- the age of nature.

♪♪ -Strait Watch, Strait Watch.

-Strait Watch, go ahead.

-Hi, I just wanted to let you know we're coming on scene here and we're just gonna do some distant fluke follows.

-For 15 years, Dr. Deborah Giles has been studying this community of orcas.

-Gosh, the southern resident killer whale population is critically endangered.

We only have 73 individuals at this point.

-Records show this is the lowest they've been for 40 years.

-I've dedicated my professional life to trying to study them to try and help answer questions that will lead to, hopefully, their recovery.

-Giles works with an unusual research assistant... -Let's get her out.

Okay, baby.

[ Dog barks ] -...Eba the orca dog.

-Good girl!

Let's get it!

[ Dog whimpers, barks ] -Eba, it's okay.

-She plays a vital role, sniffing out orca feces.

-Oh, my goodness.

Are you gonna get a poop?

[ Barking ] Are you gonna do it?

Good girl!

Let's get it.

-This is it.

-Yeah.

-This is it.

She took me to it!

Good job, good job.

Good job.

Nice!

-Did you get that one?

-This is like gold.

It really is like gold.

We can learn so much about this population of animals.

-The fecal samples reveal something surprising.

These orcas are feeding almost exclusively on one species of fish -- Chinook salmon.

-The sad thing is that through the millennia, 700,000 or more years, Chinook salmon was humongous and abundant, and it was plenty to keep a large population of killer whales thriving.

But within 150 years, we have completely decimated almost all wild Chinook salmon runs that these whales would have relied on.

-The whales are severely malnourished.

The samples of their feces can help explain why.

-The thing that samples like this can tell us is what actually -- what is this?

What was this meal?

So, was it salmon?

If it was salmon, what species of salmon?

And also, in some cases, if it's not too degraded, what river it came from.

And not only what river, but even what tributary it came from.

It's like a gold mine.

-Chinook salmon spend most of their lives at sea, but return to the rivers of their birth to spawn.

Rivers like this one -- the Elwha in Washington state.

♪♪ It flows through the old-growth forest of Olympic National Park.

♪♪ ♪♪ These streams and tributaries always provided a safe sanctuary for the Chinook salmon to breed.

But 100 years ago, everything changed.

Two hydroelectric dams were installed on the Elwha River to power industrial growth.

Migrating salmon now faced an impassable barrier.

Unable to get further up the river, the survival and reproduction of the salmon was severely compromised.

Robert Elofson is from the Lower Elwha Klallam Tribe, who have lived here for generations.

-I worked in the Park Service 40 years ago, and when you were above the dams, you never saw any salmon.

I would sit there and think what a beautiful river it is, and except there's no salmon in it.

-It wasn't always like this.

-Before the dams were built, there are stories about enough -- there being enough salmon in the river that you could walk across their backs, they were so thick.

-The size of them was also remarkable.

A fish could weigh up to 100 pounds.

♪♪ The Lower Elwha Klallam Tribe had relied on salmon for centuries, so they campaigned to get them back.

-The fight to get the dams removed took about 35 years.

It began in the 1980s.

That's when the environmental groups and the tribe started work for a phase-out removal and acquisition of the dams.

-It was time for the dams to go.

[ Explosion ] ♪♪ In 2014, the river was free again.

But no one knew if and when the wild fish would return.

-I love being out here with these fish.

-John McMillan is a fish scientist studying the recovery of the river.

-The past 10 years working on the Elwha, I'd say, have been probably the most special in my whole life.

I think when I add it up, I've snorkeled about 1,800 miles, so a lot of time in the water.

And now that we've opened up over 70 miles of new habitat, we're starting to see the Chinook salmon really take off.

I believe that my counts of juvenile Chinook salmon have tripled from what they were three years ago.

-John has now recorded a spawning run of nearly 8,000 fish and seen them in headwaters 60 miles upstream.

-Wow, there are a lot of fish in there, both juveniles and adult Chinook.

And so far, it's looking like it's gonna be an awesome year, so I'm excited about that.

♪♪ -This rise in salmon numbers has a far-reaching impact on the whole forest.

The salmon bring vital marine-derived nutrients upriver... ♪♪ ...providing a wealth of food for others living here.

And their decomposing bodies put vital nitrogen and phosphorus into the soil, enabling the trees to grow three times faster than without them.

-Large-bodied, abundant fish provide nutrients and food sources literally for the whole ecosystem -- everything from animals that are here in freshwater, from the insects to the birds, to the orcas and seals that live out there in the ocean.

These salmon are literally a keystone species that connects the marine world to the freshwater world.

♪♪ -The governor of the state of Washington, Jay Inslee, has environmental issues high on his agenda.

-Well, the Elwha Dam project, when it first came up as an idea, it's like many ideas -- it was revolutionary.

It has been such a thrill to see Mother Nature recovering now that they've been removed.

I can't think of a more inspirational place or story than to see Mother Nature coming back like a freight train.

♪♪ -Things are improving, but we don't yet know if it's enough to help the orcas.

-Orcas are in a very fragile position right now, but we're not done yet, and it's like many things -- we just need to go faster.

-Governor Inslee has issued an executive order putting together a committee of scientists and dedicating a budget of $1 billion to try and save this endangered population.

♪♪ ♪♪ -You only get one shot to prevent extinction, and so we got to make sure we go faster than we are even today.

♪♪ -Understanding how ecosystems are connected is a big part of restoring nature.

♪♪ Life is a complex web where every creature has its place.

♪♪ As we learn more about what that is, we're in a better position to look after them.

♪♪ Professor Fu Xinhua has dedicated his career to studying an endangered insect.

He's created a lab in the Huazhong Agricultural University to breed them safely.

-We have about 0.3 million larvae in this lab.

-He's the only scientist in China breeding these tiny creatures.

-It took us about six years to set up this breeding lab.

I'm quite proud of my work.

-These insects were once found all across rural China.

Today, they are incredibly rare.

But Professor Fu knows where to find them.

-Now we have to wait for the dark.

♪♪ ♪♪ -Fireflies.

♪♪ ♪♪ When courting, they produce a spectacle of light.

♪♪ -In 2005, I went to Sichuan to find fireflies and I found a plum with many fireflies, like stars falling in the trees.

I felt very excited because I had never seen such beautiful things.

♪♪ One year later, when I went back, the tree was still there, but the firefly were gone.

I felt very disappointed and sad.

That moment made me realize that I should do some works to save firefly.

-Because of rural development and increased pollution, fireflies are in decline all across China.

[ Insects buzzing, footsteps crunching ] -I realized something had to be done.

It was a race against time.

I collected eight of the fireflies and took them back to my lab to breed them.

♪♪ ♪♪ -Professor Fu needed a safe place to release the new larvae.

He chose an agricultural area around a village in Hubei province.

But first, he needed to win over the villagers.

♪♪ -When I first spoke to farmers, they thought firefly were pests and they didn't like them.

I needed to get the local people on my side.

-Xu Tanghui is the head of the village.

[ Speaking Chinese ] -Professor Fu explained that the opposite was true.

They are a natural pest control for the farmers because they eat slugs and snails.

Fireflies are an important part of the ecosystem.

But their larvae can only survive in clean water.

For the reintroduction to be successful, the farming community had to lend a hand.

[ Speaking Chinese ] ♪♪ Insects are essential for a healthy ecosystem.

Some are pollinators.

Others, predators.

♪♪ And they're food for other animals.

♪♪ Now nature is recovering.

The farmers are also doing well.

They're selling their rice as organic firefly rice, which fetches a higher price at the market.

[ Speaking Chinese ] ♪♪ What Professor Fu has achieved here is remarkable.

But it's only the first step.

-So far, we have created an area 22 square kilometers in size.

It's a place where man and nature live again in peace.

-He now has plans to roll out similar projects across the country.

-Because fireflies are very important to nature, I hope many people see fireflies sparkling all around China.

♪♪ -It takes a lot of time and effort to reintroduce wildlife.

But it's essential for our planet.

And it's happening all over the world.

♪♪ We're putting endangered animals back into their natural habitats.

♪♪ ♪♪ It can be very successful... ...but sometimes controversial.

Wolves.

We've had an uneasy relationship with these predators for a long time.

[ Cattle mooing ] ♪♪ Dean Petersen is a fourth-generation rancher in Montana.

-I woke up one morning to two wolves chasing 15 to 20 cows, just out from my house.

So I went to the other room, got a gun, walked out, leaned over my yard fence, and shot one.

-Dean and his son Malcolm run 800 cattle over 6,000 acres of pasture bordering wolf territory.

-Last winter, on the upper end of the valley here, there was one pack of six to eight wolves and they were harassing a rancher's cattle right by his house, that he was feeding.

And I don't remember how many confirmed kills there was, but the rancher claims 14 to 18 cows dead.

-It's always been tough.

At the turn of the 19th century, wolves were persecuted here to the brink of extinction.

-I've never hated them, but I've always admitted they're hard to ranch around or live around 'cause they cost you money and they cost you time and work.

It is a part of living in this valley or living in an unpopulated area.

That's where you're gonna have wolves.

There is a mindset that people hate wolves, and I...

I don't know why.

They're just another one of the creatures that are here on the Earth, and they're part of the ecosystem, just like I'm part of the ecosystem at this point in time.

And I can accept them.

But I'm gonna get -- I'm gonna be part of the rules that control them, too.

♪♪ -Dean only faces these issues today because of a pioneering restoration project which began 25 years ago in nearby Yellowstone National Park.

♪♪ ♪♪ Doug Smith was a key part of the project from the beginning.

-Well, this is one of the most beautiful areas in Yellowstone.

I've been here 25 years and I've always loved this little spot.

We've got bison all through the valley, we've got elk, we've got deer, we've got grizzly bears, black bears.

I mean, this is as good as it gets for America.

I've been interested in wolves since I was a small boy, so I started working with wolves at 18 years of age.

So this is my 40th year studying wolves.

-After a long campaign, the reintroduction of wolves to Yellowstone was a special moment for Doug.

-Here they come.

Yeah, this is history here.

January 1995.

Big day.

-The park was chosen as a suitable location because of its size and the large amount of prey.

-So we went to Canada, where there were a lot of wolves and we caught wolves there.

We brought them down here to Yellowstone.

♪♪ So, bringing in 41 wolves like we did was enough to jump-start it.

Now we're a self-sustaining population.

-Today, there are about 500 wolves across the Greater Yellowstone area.

And they're having a huge impact on the landscape.

-We're pretty close.

It should be along this trail.

So, we're looking for any sign of disturbance, maybe some hide and different bones that are left over after wolves or bears have been at a carcass site.

[ Flies buzzing ] -Jack Rabe is a scientist studying the effect wolves have on other animals.

-So, here we have the lower jaw from a yearling bison.

One huge thing that comes from wolves making kills is it feeds a whole ecosystem.

So, a lot of times these carcasses bring in different scavengers like ravens, eagles, coyotes, fox, bears.

[ Bear growls ] [ Wolf whimpering ] -The wolves here are actually helping other predator populations to increase.

[ Pups squeaking ] Because of the way they hunt, wolves can even benefit their prey, like elk and bison.

-Wolves, they're what we call coursing predators.

Once they send the prey running, it's gonna be much easier for them to target, you know, a weaker individual that's gonna be also an easier target for them to hunt.

So we've seen overall healthier populations within elk and bison.

-And wolves do something even more important.

-We call this "landscape of fear," where it changes the behavior of elk or the behavior of bison.

They have to be more vigilant.

They have to be on the lookout for different predators, which means, you know, they can't sit down in the valleys and graze and, you know, not have to worry about wolves on the landscape.

-Elk, deer, and bison no longer stay in the open, so the areas they once overgrazed are able to recover.

The return of the wolves is transforming the landscape.

♪♪ -And now we see a great abundance of willow and aspen in many different places.

And there was a signal of songbirds coming back, as well.

It's filled with birds, and that's not what it was like 25 years ago.

♪♪ ♪♪ And so I think back to the moment of letting those wolves go a lot.

Here I am in younger days, better shape.

Could carry a wolf.

That was fun.

This was one of the most famous photos.

It really captures the essence of a wolf.

This is the beginning of the Yellowstone story.

The wolf's looking out into Yellowstone.

We don't know how it's gonna turn out.

Is it gonna work?

Is it gonna be successful?

Certainly, Yellowstone's a better place now with wolves back.

The ecosystem's more whole.

Helping to restore a species that we wiped out feels very good.

But looking back on this is a strong sense of satisfaction that you've been part of something bigger than you.

♪♪ -Wolves are now spreading across America, reclaiming old territory.

They've got the space to do so.

But in Europe, where wolves are returning of their own accord, the space is limited.

They've recently arrived in the Netherlands, home to 17 million people.

♪♪ Much of the land is taken up by intensive agriculture and industry... ♪♪ ...leaving little room for wildlife.

♪♪ Despite this, the first few wolves are beginning to return.

♪♪ [ Sheep bleating ] -[ Whistles ] Come-bye!

Come-bye!

-Daphne van Zomeren looks after her sheep not far from Amsterdam, where one of them has been sighted.

[ Whistles ] -I think it's very special that the wolf is back in the Netherlands.

I'm really not afraid of the wolf.

I think he's more afraid of us.

[ Sheep bleating ] I can't imagine that he would come here and catch one of my sheep when I'm with them.

-And when she's not with them, Daphne secures the flock behind an electric fence.

There's only one wolf here at the moment, but she's not taking any risks.

-It's very important that all the shepherds protect their sheep.

Then the wolf won't kill them.

And then there is a more positive feeling about wolf.

♪♪ -Ecologist Hugh Jansman is out looking for signs of wolf activity.

-Since 2015, we see more and more frequently wolves settling here.

But the idea that this system is now being influenced by such a top predator, well, it definitely adds to the excitement, I'd say.

-By analyzing wolf scats, Hugh can learn a lot about their behavior.

-This wolf has been eating wild boar.

I can tell from the hair structure.

And here you can see a bone fragment.

We take a DNA sample.

and then we want to know if it is the female, and that gives us information about our territorial status.

She is probably settling down.

So, yeah, very important.

-His studies show that, so far, this female wolf is only preying on wild animals.

-Now we have wolves already surviving for more than half a year in this country without killing sheep in these areas.

Yeah, good news.

Very good for the ecosystem.

-Only three wolves have settled in the Netherlands so far.

It's early days in the relationship.

Time will tell if we can coexist, and whether the wolves will benefit this landscape.

[ Birds chirping ] ♪♪ All around the world, we're helping nature to recover.

♪♪ And the foundations of life are the plants and trees.

♪♪ Many restoration projects begin with planting, which can kick-start the ecosystem.

But it is a complex process, as every place is different, with unique soils and climate.

The hardest places to restore are those that have laid bare for hundreds of years.

♪♪ -Like many people, I grew up in Scotland thinking that these wide-open landscapes, these vast expanses of grass and heather were natural, that was the way it was always supposed to be.

It's only since I've been an adult that I've learned there's something seriously wrong here.

There's something very fundamental missing from this view.

-Much of Scotland looks like this -- wild and rugged.

But it's actually a heavily degraded landscape.

-This is what we call a peat hag.

This is a gaping wound.

It's an open sore on the land.

And what happens is, you know, the surface vegetation gets broken up and deer trample and so forth, and then erosion takes place, the vegetation gets washed away, and the bare peat gets exposed.

This was much more full of life in the past.

And today, nothing can survive here.

And there's leaching of carbon, as well, that's stored in the peat, and there's no vegetation to store it.

So it's actually contributing to climate change, as well.

-These tree stumps are clues to the past.

This was once woodland.

Today, the hillsides are bare and much of Scotland's native wildlife is missing.

♪♪ But one species is thriving.

Red deer.

Innes MacNeill is head ranger at the Alladale Wilderness Reserve.

-Well, I guess what people have forgotten that historically red deer were a forest animal.

But as you can see, the forest is well and truly gone.

So to my mind, deer -- deer are the success story.

They've adapted, and they love an open range now.

[ Deer bellowing ] -Thousands of years ago, agricultural development led to the clearing of Scotland's forests.

By the 18th century, they were virtually gone.

-There's not a lot of forest left.

They say that there's between 2% and 6% of the original forests.

It's not the deer to blame for that.

It's man that did that damage.

-But today, deer prevent the forest from regenerating because they eat young saplings.

And numbers are so high, it's Innes' role to try to keep the population in check.

-[ Whispering ] Get down, get down, get down, down, down!

Alright, it's too good a chance.

Can you see them?

Just be careful, careful, careful.

[ Gun cocks ] [ Gunshot ] -Each year, Innes and his team kill up to 350 deer on this estate.

The work is difficult, but necessary.

-Some people will probably find it, you know, hard to understand that we do respect the deer when we cull so many of them.

But you've got to switch off to that part.

I guess it's worth taking on the role of the predator.

We don't have any large apex predators in Scotland, so it's our role to manage the deer population and keep it, you know, in sync with the habitat.

♪♪ -This action allows forests a chance to recover naturally... ...so that more of Scotland may one day look like this again.

♪♪ Glen Affric -- a beautiful land of ancient forest.

♪♪ -This is what most of Scotland would have looked like, in the Highlands at least, several thousand years ago, and now we've got less than 1% of this old forest left in scattered fragments.

And Glen Affric is one of the best of those.

It's the largest extent of least disturbed forest in the U.K.

So it's a very special place.

♪♪ -Alan knows how important this ancient forest is to Scotland's native wildlife.

He also knows how little there is left.

♪♪ -And I thought somebody should do something about this.

And for some time, I kept getting this feeling, until eventually it dawned on me, "Well, maybe the somebody is me.

[ Chuckling ] Maybe I need to do something about this."

-In the early '90s, Alan set up a charity and began planting.

He installed fences to keep out deer and sheep to safeguard the young saplings.

-So, here inside the fence, there's been no grazing for 28 years now.

So, this is one of the first Scots pines that I planted here in Glen Affric 28 years ago.

And at the time, this area was a desolate, open, barren, treeless landscape, just like the peat hag outside here.

And this tree has grown really well.

It's now putting on over a foot of growth a year.

It's really flourishing.

-Within Alan's enclosure, the whole ecosystem is regenerating.

-This is bog myrtle.

It's an aromatic shrub.

It's also highly palatable to deer, so we don't find much of it outside the fence.

It's important because it has bacteria in its roots that fix nitrogen from the air and it fertilizes and improves the soil.

It dries out the ground and it helps make way for the pioneer trees like the birch and rowans and willows to follow.

So this is the process of ecological recovery, the process of natural succession, which shows that this ecosystem is returning to health and balance again.

-Alan himself has planted 50,000 trees.

The charity, nearly 2 million.

-So it gives me a great sense of hope and positivity for the future that I'm passing on to future generations a land that is going to be rich and diverse and healthy again.

-And Alan's not the only one.

Across Scotland, the rewilding movement is gathering momentum.

Beavers are being reintroduced.

Pine martens and osprey are naturally returning.

♪♪ ♪♪ The benefits of these restored forests are clear... ...increasing biodiversity... ...reducing the impact of floods... ...and absorbing carbon.

Healthy forests, rather than degraded land, cope better with a changing climate.

♪♪ [ Chainsaw starting ] But the wrong trees in the wrong place can be catastrophic.

♪♪ The Western Cape in South Africa is famous for its ancient ecosystem called fynbos.

It has over 9,000 plant species, many of which are found nowhere else on Earth.

They support a great diversity of wildlife, from insects to birds and mammals.

♪♪ ♪♪ The fynbos is critical for the city of Cape Town, which in 2018 was facing a disaster.

After three years of drought, it was days away from zero water.

-Well, 2018, there was a very real risk of the city potentially running out of water.

-Councillor Limberg was the official in charge of preparing for this situation.

-The city did have to take very tough decisions during the height of the drought, and this is why we declared a local disaster.

-It didn't matter where you lived -- beachside suburbs or townships, everyone was affected.

-There was risk of greater health issues around sanitation, particularly, and a potential risk of lawlessness and violence.

-To conserve water, everyone was restricted to 13 gallons per day.

Nontombi Lubisi runs a car washing business in the Khayelitsha Township.

♪♪ Water restrictions were threatening livelihoods in a country where 50% of people live in extreme poverty.

It was potentially devastating.

♪♪ Cape Town gets all its water from the fynbos ecosystem in the mountains that surround the city.

And the fynbos itself can cope with intermittent rainfall because most of its moisture comes from regular coastal fog when cold air from the ocean condenses over the warm land.

It's worked like this for millions of years.

But in this finely tuned landscape, there are invasive species upsetting the balance.

Alien plants.

-Oh, yes, here's a small pine.

It's always good to get them when they're still this size because it's easy to hand-pull them.

So, slow pull, and out.

There it is.

It shows quite a big root system already, even though this pine is not even yet a year old.

-Louise Stafford, water director at the Nature Conservancy, is an expert on the ecosystem here.

-Most of the invasive species that we find in the watersheds of the Cape Town region come from Europe and Australia.

-The pine tree was introduced 200 years ago for its timber.

-In comparison to fynbos, the pine trees are huge trees with deep taproot systems, and they actually use more water than the native species.

And if you look at the system in Cape Town, about 70% of the watershed upon which Cape Town depends for its water is invaded by alien plants.

♪♪ The region is losing 55.5 billion liters of water every year as a result of alien plants in the catchments.

And it equates to about two months' water supply just for the city of Cape Town itself.

-The war against these aliens is on.

[ Helicopter blades whirring ] A specially trained team is taken to the most inaccessible places.

-Come on, guys.

We're gonna chop down some trees at the bottom there.

Cedric November and Po Malawu are part of the team.

I'm cutting because this pine tree was drinking 200 liters in the day, water.

-I would say it's very important because by cutting down this that is taking such much water from our country and our land, it's actually saving lives.

-Each pine tree can drink up to 9 gallons of water a day -- almost as much as people were allowed during the crisis.

[ Chainsaw whirring ] [ Saw rasping ] It's estimated that these clearing efforts so far have saved over 6.5 million gallons of water.

♪♪ ♪♪ But there's no short-term fix.

The invasive seeds can lie dormant for many years.

-So it is very labor-intensive, very time-consuming, and a very costly exercise.

But if we don't do that, the losses will continue and even increase -- something that this region can ill afford.

-In 2018, the rains did eventually come, but well below expected levels.

It was just enough to avert the crisis -- this time.

Cape Town isn't the only city struggling.

Many others around the world are under severe water stress.

♪♪ Extreme weather like this is becoming more frequent because of a huge environmental challenge that the whole world now faces.

♪♪ Climate change.

♪♪ Research shows the healthier the ecosystem, the better it can cope.

♪♪ In this new era of understanding, we know that the more of nature we can restore, the brighter the future for our planet.

♪♪ ♪♪ -To order "The Age of Nature" on DVD, visit shopPBS or call 1-800-PLAY-PBS.

This program is also available on Amazon Prime Video.

♪♪ ♪♪