How a 19th-century doctor saved New York–by planting trees

Updated: May 14, 2020

Trees are everywhere in cities nowadays, but that wasn’t always the case. And their role in protecting cities has never been more crucial.

Many cities, in recent years, have initiated tree-planting campaigns to offset carbon dioxide emissions and improve urban microclimates.

In 2007, New York City launched MillionTrees NYC, a program designed to plant 1 million new trees along streets, in parks, and on private and public properties by 2017. They hit their goal two years ahead of time.

These programs are popular for a reason: Not only do trees improve the city’s appearance, but they also mitigate the urban heat island effect–the tendency for dense cities to be hotter than surrounding areas. Studies have shown that trees reduce pollutants in the air, and even the mere sight of trees and the availability of green spaces in cities can decrease stress.

But as I show in my new book, Seeing Trees: A History of Street Trees in New York City and Berlin, trees weren’t always a part of the urban landscape. It took a systematic, coordinated effort to get the first ones planted.


As New York City’s population exploded in the 19th century, poor sanitary conditions, overcrowding, and hot summers made the city a petri dish for disease: Between 1832 and 1866, cholera outbreaks alone had killed an estimated 12,230 people.

By the turn of the 20th century, living conditions had deteriorated. Neighborhoods continued to be overcrowded, indoor plumbing was still lacking, and open sewers could still be found along many of the city’s dusty streets and alleys.

Trees could be entirely absent from a neighborhood. The few trees that did line city streets–mostly ailanthus, elms, and buttonwoods–could be individually cataloged with relatively little effort. For example, in 1910, the New York Times reported on the decreasing number of trees along Fifth Avenue. The article noted that between 14th Street and 59th Street, there were only seven trees on the west side and six on the east side of the avenue.

Real estate development, subway expansion, and utility line construction had clearly taken their toll.


In the 1870s, eminent New York City physician Stephen Smithspearheaded a movement to plant more trees. Doing so, he argued, would save lives.

To promote tree planting in his city, Smith drew attention to what became known as the Washington Elm study. Smith, who pioneered the city’s sanitary reforms and founded the Metropolitan Board of Health, was the author of a groundbreaking study that correlated high temperatures with childhood deaths from a number of infectious diseases. He concluded that planting street trees could mitigate oppressive heat and save 3,000 to 5,000 lives per year.

Attributed to Harvard College mathematics professor Benjamin Peirce, the study claimed that the famous Washington El