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.