From the top of the food chain down: Rewilding our world - George Monbiot

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Our planet was once populated by megafauna, big top-of-the-food-chain predators that played their part in balancing our ecosystems. When those megafauna disappear, the result is a "trophic cascade," where every part of the ecosystem reacts to the loss. How can we stay in balance? George Monbiot suggests rewilding: putting wolves, lions and other predators back on top -- with surprising results.

Lesson by George Monbiot, animation by Avi Ofer.

We all know about the dinosaurs

that once roamed the planet,

but long after they went extinct,

great beasts we call the megafauna

lived on every continent.

In the Americas, ground sloths the size of elephants

pulled down trees with their claws.

Saber-toothed cats the size of brown bears

hunted in packs,

but they were no match for short-faced bears,

which stood thirteen feet on their hind legs,

and are likely to have driven these cats

away from their prey.

There were armadillos as big as small cars,

an eight foot beaver,

and a bird with a 26 foot wingspan.

Almost everywhere, the world's megafauna

were driven to extinction, often by human hunters.

Some species still survive in parts of Africa and Asia.

In other places, you can still see the legacy of these great beasts.

Most trees are able to resprout

where their trunk is broken

to withstand the loss of much of their bark

and to survive splitting, twisting and trampling,

partly because they evolved to survive attacks by elephants.

The American pronghorn can run so fast

because it evolved to escape the American cheetah.

The surviving animals live in ghost ecosystems

adapted to threats from species that no longer exist.

Today, it may be possible to resurrect those ghosts,

to bring back lost species using genetic material.

For instance, there's been research in to

cloning woolly mammoths from frozen remains.

But even if it's not possible,

we can still restore many of the ecosystems

the world has lost.

How? By making use of abandoned farms.

As the market for food is globalized,

infertile land becomes uncompetitive.

Farmers in barren places can't compete

with people growing crops on better land elsewhere.

As a result, farming has started to retreat from many regions,

and trees have started to return.

One estimate claims that two-thirds of land in the US

that was once forested but was cleared for farming

has become forested again.

Another estimate suggests that by 2030,

an area in Europe the size of Poland

will be vaccated by farmers.

So even if we can't use DNA to bring back

ground sloths and giant armadillos,

we can restore bears, wolves, pumas

lynx, moose and bison

to the places where they used to live.

Some of these animals can reshape their surroundings,

creating conditions that allow other species to thrive.

When wolves were reintroduced to

the Yellowstone National Park in 1995,

they quickly transformed the ecosystem.

Where they reduced the numbers of overpopulated deer,

vegetation began to recover.

The height of some trees quintupled in just six years.

As forests returned, so did songbirds.

Beavers, which eat trees, multiplied in the rivers,

and their dams provided homes

for otters, muskrats, ducks, frogs and fish.

The wolves killed coyotes, allowing rabbits

and mice to increase,

providing more food for hawks, weasels,

foxes and badgers.

Bald eagles and ravens fed on the carrion

that the wolves abandoned.

So did bears, which also ate the berries

on the returning shrubs.

Bison numbers rose as they browsed

the revitalized forests.

The wolves changed almost everything.

This is an example of a trophic cascade,

a change at the top of the food chain

that tumbles all the way to the bottom,

affecting every level.

The discovery of widespread trophic cascades

may be one of the most exciting scientific findings

of the past half century.

They tell us that ecosystems that have lost

just one or two species of large animals

can behave in radically different ways

from those that retain them.

All over the world, new movements are trying

to catalyze the restoration of nature

in a process called rewilding.

This means undoing some of the damage we've caused,

reestablishing species which have been driven out,

and then stepping back.

There is no attempt to create an ideal ecosystem,

to produce a heath, a rainforest or a coral reef.

Rewilding is about bringing back the species

that drive dynamic processes

and then letting nature take its course.

But it's essential that rewilding must never be used

as an excuse to push people off the land.

It should happen only with the consent

and enthusiasm of the people who work there.

Imagine standing on a cliff in England,

watching sperm whales attacking shoals of herring

as they did within sight of the shore

until the 18th century.

By creating marine reserves

in which no commerical fishing takes place,

that can happen again.

Imagine a European Serengeti

full of the animals that used to live there:

hippos, rhinos, elephants, hyenas and lions.

What rewilding reintroduces,

alongside the missing animals and plants,

is that rare species called hope.

It tells us that ecological change

need not always proceed in the same direction.

The silent spring could be followed by a wild summer.