urban forest
n. The collection of trees found within a city's limits.
"Metro Atlanta is losing 50 acres of tree cover per day to make way for new housing, roads, shopping malls and office parks, according to an analysis of satellite images.

And as its urban forest disappears, metro Atlanta's misery level rises—more heat, more flooding, more air pollution, higher electric bills.
—Charles Seabrook, “Scalping of the land makes Atlantans hot,” The Atlanta Journal and Constitution, February 19, 1999
1980 (earliest)
They quiet city noise, and help clean fouled air. They can save precious energy by raising a city's temperature in the winter, and cooling things down in the summer. They can raise property values, and keep jobs and people from fleeing cities. They also happen to be beautiful. If they sound like some weird combination of air filter, heater, air conditioner and attractive city booster, they are, in a way.

They're trees.

And since January, the city of Dayton, Ohio, has been taking stock of the benefits and costs of its "urban forest."
—Lee Mitgang, “The Greening of Dayton,” The Associated Press, April 30, 1980
According to forestry experts — and as is well known by those who live or work on the upper floors in high-rise buildings - trees cover about 30% of the land in most cities.