0:00:07.484,0:00:14.071
This is the tale of two ancient cities and[br]the trees that determined their destinies.

0:00:14.071,0:00:19.930
In 3,000 BC Uruk was more densely [br]populated than modern day New York City.

0:00:19.930,0:00:24.802
This crowded capital had to continually[br]expand their irrigation system

0:00:24.802,0:00:26.902
to feed its growing population.

0:00:26.902,0:00:33.784
2,500 years later in Sri Lanka, the city [br]of Anuradhapura had a similar problem.

0:00:33.784,0:00:36.246
They were also growing constantly,

0:00:36.246,0:00:42.019
and like Uruk, their city relied heavily [br]on an elaborate irrigation system.

0:00:42.019,0:00:48.290
As Uruk grew, its farmers began chopping [br]down trees to make space for more crops.

0:00:48.290,0:00:51.543
In Anuradhapura, however, [br]trees were sacred.

0:00:51.543,0:00:54.843
Their city housed an offshoot of the Bodhi[br]tree

0:00:54.843,0:00:59.112
under which Buddha himself was said[br]to have attained enlightenment.

0:00:59.112,0:01:02.212
Religious reverence slowed farmer’s [br]axes

0:01:02.212,0:01:06.947
and even led the city to plant additional[br]trees in urban parks.

0:01:06.947,0:01:10.146
Initially, Uruk’s expansion worked well.

0:01:10.146,0:01:13.326
But without trees to filter their water [br]supply,

0:01:13.326,0:01:16.706
Uruk’s irrigation system [br]became contaminated.

0:01:16.706,0:01:19.556
Evaporating water left mineral deposits,

0:01:19.556,0:01:23.080
which rendered the soil [br]too salty for agriculture.

0:01:23.080,0:01:27.390
Conversely, Anuradhapura’s irrigation [br]system was designed to work

0:01:27.390,0:01:29.890
in concert with the surrounding forest.

0:01:29.890,0:01:34.120
Their city eventually grew to more than [br]twice Uruk’s population,

0:01:34.120,0:01:40.773
and today, Anuradhapura still cares for [br]a tree planted over 2,000 years ago.

0:01:40.773,0:01:44.912
We may think of nature as being [br]unconnected to our urban spaces,

0:01:44.912,0:01:49.657
but trees have always been an essential[br]part of successful cities.

0:01:49.657,0:01:53.974
Trees act like a natural sponge, absorbing[br]storm water runoff

0:01:53.974,0:01:56.782
before releasing it back into[br]the atmosphere.

0:01:56.782,0:01:59.562
The webs of their roots protect against [br]mudslides

0:01:59.562,0:02:03.639
while allowing soil to retain water and[br]filter out toxins.

0:02:03.639,0:02:05.669
Roots help prevent floods,

0:02:05.669,0:02:09.598
while reducing the need for storm [br]drains and water treatment plants.

0:02:09.598,0:02:14.761
Their porous leaves purify the air by [br]trapping carbon and other pollutants,

0:02:14.761,0:02:18.351
making them essential in the [br]fight against climate change.

0:02:18.351,0:02:23.026
Humanity has been uncovering these [br]arboreal benefits for centuries.

0:02:23.026,0:02:27.132
But trees aren’t just crucial to the [br]health of a city’s infrastructure;

0:02:27.132,0:02:30.602
they play a vital role in the health of [br]its citizens as well.

0:02:30.602,0:02:36.225
In the 1870’s, Manhattan had few trees [br]outside the island’s parks.

0:02:36.225,0:02:38.215
Without trees to provide shade,

0:02:38.215,0:02:42.311
buildings absorbed up to nine [br]times more solar radiation

0:02:42.311,0:02:44.630
during deadly summer heat waves.

0:02:44.630,0:02:47.780
Combined with the period’s poor [br]sanitation standards,

0:02:47.780,0:02:53.229
the oppressive heat made the city a [br]breeding ground for bacteria like cholera.

0:02:53.229,0:02:57.943
In modern day Hong Kong, tall skyscrapers[br]and underground infrastructure

0:02:57.943,0:03:00.343
make it difficult for trees to grow.

0:03:00.343,0:03:04.223
This contributes to the city’s dangerously[br]poor air quality,

0:03:04.223,0:03:07.903
which can cause bronchitis and diminished[br]lung function.

0:03:07.903,0:03:10.213
Trees affect our mental health as well.

0:03:10.213,0:03:15.492
Research indicates that the presence [br]of green foliage increases attention spans

0:03:15.492,0:03:17.910
and decreases stress levels.

0:03:17.910,0:03:22.056
It’s even been shown that hospital [br]patients with views of brick walls

0:03:22.056,0:03:26.056
recover more slowly than [br]those with views of trees.

0:03:26.056,0:03:29.452
Fortunately, many cities [br]are full of views like this –

0:03:29.452,0:03:30.902
and that’s no accident.

0:03:30.902,0:03:32.884
As early as the 18th century,

0:03:32.884,0:03:37.619
city planners began to embrace the [br]importance of urban trees.

0:03:37.619,0:03:43.290
In 1733, Colonel James Oglethorpe [br]planned the city of Savannah, Georgia

0:03:43.290,0:03:48.241
to ensure that no neighborhood was [br]more than a 2-minute walk from a park.

0:03:48.241,0:03:53.879
After World War II, Copenhagen directed [br]all new development along five arteries –

0:03:53.879,0:03:56.509
each sandwiched between a park.

0:03:56.509,0:03:58.849
This layout increased the city’s [br]resilience

0:03:58.849,0:04:01.272
to pollution and natural disasters.

0:04:01.272,0:04:04.262
And urban trees don’t just benefit people.

0:04:04.262,0:04:08.421
Portland’s Forest Park preserves the [br]region’s natural biodiversity,

0:04:08.421,0:04:11.271
making the city home to various [br]local plants,

0:04:11.271,0:04:16.237
112 bird species, and 62 [br]species of mammals.

0:04:16.237,0:04:20.007
No city is more committed to trees [br]than Singapore.

0:04:20.007,0:04:26.353
Since 1967, Singapore’s government[br]has planted over 1.2 million trees,

0:04:26.353,0:04:32.070
including those within 50-meter tall [br]vertical gardens called supertrees.

0:04:32.070,0:04:36.070
These structures sustain themselves [br]and nearby conservatories

0:04:36.070,0:04:39.180
with solar energy and collected rainwater.

0:04:39.180,0:04:44.129
Trees and vegetation currently cover [br]over 50% of Singapore’s landmass,

0:04:44.129,0:04:46.259
reducing the need for air conditioning

0:04:46.259,0:04:49.409
and encouraging low-pollution [br]transportation.

0:04:49.409,0:04:55.331
By 2050, it’s estimated that over 65% of[br]the world will be living in cities.

0:04:55.331,0:04:58.968
City planners can lay an eco-friendly[br]foundation,

0:04:58.968,0:05:02.068
but it’s up to the people who live in [br]these urban forests

0:05:01.806,0:05:05.420
to make them homes for more than humans.