Cities Need Trees
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 its 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
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
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 1870s, 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 heatwaves. 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 neighbourhood
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 parks.
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
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.
Source: TED Ed – By Stefan Al