What happens if you cut down all of a city's trees? - Stefan Al

This is the tale of two ancient cities and
the trees that determined their destinies.

In 3,000 BC Uruk was more densely
populated than modern day New York City.

This crowded capital had to continually
expand their irrigation system

to feed its growing population.

2,500 years later in Sri Lanka, the city
of Anuradhapura had a similar problem.

They were also growing constantly,

and like Uruk, their city relied heavily
on an elaborate irrigation system.

As Uruk grew, its farmers began chopping
down trees to make space for more crops.

In Anuradhapura, however,
trees were sacred.

Their city housed an offshoot of the Bodhi
tree

under which Buddha himself was said
to have attained enlightenment.

Religious reverence slowed farmer’s
axes and even led the city

to plant additional trees in urban parks.

Initially, Uruk’s expansion worked well.

But without trees to filter their water
supply,

Uruk’s irrigation system
became contaminated.

Evaporating water left mineral deposits,

which rendered the soil
too salty for agriculture.

Conversely, Anuradhapura’s irrigation
system was designed to work

in concert with the surrounding forest.

Their city eventually grew to more than
twice Uruk’s population,

and today, Anuradhapura still cares for
a tree planted over 2,000 years ago.

We may think of nature as being
unconnected to our urban spaces,

but trees have always been an essential
part of successful cities.

Trees act like a natural sponge, absorbing
storm water runoff

before releasing it back into
the atmosphere.

The webs of their roots protect against
mudslides

while allowing soil to retain water and
filter out toxins.

Roots help prevent floods,

while reducing the need for storm
drains and water treatment plants.

Their porous leaves purify the air by
trapping carbon and other pollutants,

making them essential in the
fight against climate change.

Humanity has been uncovering these
arboreal benefits for centuries.

But trees aren’t just crucial to the
health of a city’s infrastructure;

they play a vital role in the health of
its citizens as well.

In the 1870’s, Manhattan had few trees
outside the island’s parks.

Without trees to provide shade, buildings
absorbed up to nine times more solar radiation

during deadly summer heat waves.

Combined with the period’s poor
sanitation standards,

the oppressive heat made the city a
breeding ground for bacteria like cholera.

In modern day Hong Kong, tall skyscrapers
and underground infrastructure

make it difficult for trees to grow.

This contributes to the city’s dangerously
poor air quality,

which can cause bronchitis and diminished
lung function.

Trees affect our mental health as well.

Research indicates that the presence
of green foliage increases attention spans

and decreases stress levels.

It’s even been shown that hospital
patients with views of brick walls

recover more slowly than
those with views of trees.

Fortunately, many cities
are full of views like this –

and that’s no accident.

As early as the 18th century,

city planners began to embrace the
importance of urban trees.

In 1733, Colonel James Oglethorpe
planned the city of Savannah, Georgia

to ensure that no neighborhood was
more than a 2-minute walk from a park.

After World War II, Copenhagen directed
all new development along five arteries –

each sandwiched between a park.

This layout increased the city’s
resilience

to pollution and natural disasters.

And urban trees don’t just benefit people.

Portland’s Forest Park preserves the
region’s natural biodiversity,

making the city home to various
local plants,

112 bird species, and 62
species of mammals.

No city is more committed to trees
than Singapore.

Since 1967, Singapore’s government
has planted over 1.2 million trees,

including those within 50-meter tall
vertical gardens called supertrees.

These structures sustain themselves
and nearby conservatories

with solar energy and collected rainwater.

Trees and vegetation currently cover
over 50% of Singapore’s landmass,

reducing the need for air conditioning

and encouraging low-pollution
transportation.

By 2050, it’s estimated that over 65% of
the world will be living in cities.

City planners can lay an eco-friendly
foundation,

but it’s up to the people who live in
these urban forests

to make them homes for more than humans.