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This is the tale of two ancient cities

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and the trees [br]that determined their destinies.

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

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This crowded capital had to continually[br]expand their irrigation system

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to feed its growing population.

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

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They were also growing constantly,

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

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

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In Anuradhapura, however, [br]trees were sacred.

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Their city housed an offshoot [br]of the Bodhi tree

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under which Buddha himself [br]was said to have attained enlightenment.

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Religious reverence [br]slowed farmer’s axes

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and even led the city to plant [br]additional trees in urban parks.

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Initially, Uruk’s expansion worked well.

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But without trees to filter [br]their water supply,

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Uruk’s irrigation system [br]became contaminated.

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Evaporating water left mineral deposits,

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which rendered the soil [br]too salty for agriculture.

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Conversely, Anuradhapura’s [br]irrigation system was designed to work

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in concert with the surrounding forest.

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

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

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

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

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Trees act like a natural sponge, [br]absorbing storm water runoff

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before releasing it back [br]into the atmosphere.

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The webs of their roots protect against [br]mudslides

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while allowing soil to retain water [br]and filter out toxins.

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Roots help prevent floods,

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

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

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making them essential [br]in the fight against climate change.

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Humanity has been uncovering [br]these arboreal benefits for centuries.

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

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

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

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Without trees to provide shade,

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buildings absorbed up to nine times [br]more solar radiation

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during deadly summer heat waves.

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Combined with the period’s [br]poor sanitation standards,

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

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In modern day Hong Kong, tall skyscrapers[br]and underground infrastructure

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make it difficult for trees to grow.

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

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which can cause bronchitis [br]and diminished lung function.

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Trees affect our mental health as well.

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Research indicates that the presence [br]of green foliage increases attention spans

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and decreases stress levels.

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

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recover more slowly than [br]those with views of trees.

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Fortunately, many cities [br]are full of views like this—

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and that’s no accident.

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As early as the 18th century,

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city planners began to embrace [br]the importance of urban trees.

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

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

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After World War II, Copenhagen directed [br]all new development along five arteries—

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each sandwiched between a park.

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This layout increased [br]the city’s resilience

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to pollution and natural disasters.

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And urban trees don’t just benefit people.

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Portland’s Forest Park preserves [br]the region’s natural biodiversity,

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making the city home to various [br]local plants,

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112 bird species, [br]and 62 species of mammals.

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No city is more committed to trees [br]than Singapore.

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

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

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These structures sustain themselves [br]and nearby conservatories

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with solar energy and collected rainwater.

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

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reducing the need for air conditioning

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and encouraging low-pollution [br]transportation.

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

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City planners can lay an eco-friendly[br]foundation,

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

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to make them homes for more than humans.