By 2050, it's estimated that over 65% of the world will be living in cities. We may think of nature as being unconnected to our urban spaces, but trees have always been an essential part of successful cities. Humanity has been uncovering these arboreal benefits since the creation of our first cities thousands of years ago. So what makes trees so important to a city's survival? Stefan Al explains. [Directed by Mette Ilene Holmriis, narrated by Addison Anderson, music by Bamm Bamm Wolfgang].