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This is the tale of two ancient cities and[br]the trees 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 of the Bodhi[br]tree

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

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

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to plant additional trees in urban parks.

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Initially, Uruk’s expansion worked well.

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But without trees to filter their water [br]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 irrigation [br]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 for [br]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 an essential[br]part of successful cities.

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

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before releasing it back into[br]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 and[br]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 by [br]trapping carbon and other pollutants,

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

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

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

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they play a vital role in the health of [br]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, buildings[br]absorbed up to nine times more solar radiation

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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.