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.