A million new trees: NYC leaders must look at where — not just how many
February 14, 2022
New York City’s five borough presidents are calling on Mayor Eric Adams to plant a million new trees by 2030. It’s an effort to revive the “million trees” initiative that began under Mayor Michael Bloomberg, and to aid New Yorkers who are increasingly subjected to extreme heat. The following Cornell University experts are available to interview on the benefits and risks associated any new tree planting initiative.
J. Meejin Yoon, dean of the College of Architecture, Art, and Planning at Cornell University, says the location of newly planted trees is just as important as how many.
“Street trees are a crucial layer of distributed urban infrastructure, vital to confronting the challenges posed by climate change and urban heat islands faced by cities around the world. As with other forms of infrastructure, street trees have historically been deployed unevenly, exacerbating the inequities of the city and disproportionally exposing vulnerable communities to the effects of climate change.
“Where the next generation of street trees are planted is as important as how many are planted. A spatial data visualization tool developed by the Cornell Design Across Scales Lab works to examine urban data sets and LIDAR Scans to examine the aggregate of all urban street trees and identify historic inequalities and inform tree planting initiatives to move beyond headline numbers of trees planted.
“These headline numbers are often achieved in areas that are the easiest and most affordable for the city to plant in, failing to deliver shade where it is the most needed.
“Individual trees have highly local impacts, including shading buildings, sidewalks, and public spaces, and improving air quality along high-traffic streets. These cumulative effects give value to a city. Developing modern tools to study these impacts and plant based on equity and effectiveness is vital to a city’s future.”
Nina Bassuk, professor and program leader of the Urban Horticulture Institute at Cornell University, says urban planners can learn from past mistakes and utilize new research to maximize the benefits of trees in urban settings.
“The benefits of trees in urban areas are known: They reduce heat during the hottest times of the year; they reduce the number of heat-associated deaths; they reduce stormwater surge that can overwhelm combined storm and sanitary sewers that contribute to flooding and dumping of waste into our rivers. And trees have many other ecosystem benefits.
“However, as was shown during the last Million Tree planting efforts undertaken during the Bloomberg administration, approximately 25% of the trees died or were missing shortly after planting. This is a tremendous loss since the greatest tree benefits are caused by the growth of a large canopy of leaves. We need trees to grow and thrive if they are to produce these benefits.
“So, what can we do? First we need to create spaces where there is enough soil for roots to grow. In paved sidewalk areas where there is a small volume of useable soil we can expand soil under the sidewalk to increase tree rooting volume. CU-Structural Soil developed at Cornell University meets the engineers’ need of a load bearing surface for pavement while allowing tree roots to grow under the sidewalk.
“We can also plant a diversity of trees that will withstand the stresses that come with heat, flooding, and drought that are part of the urban environment and getting worse in the face of climate change. By diversifying tree species, we reduce the effects of an insect or disease that feeds on one tree such as the Emerald Ash Borer. The third part of the effort should include timely management and protection of trees as they begin to grow or are at the end of their useful life. We can do a lot more to increase our urban tree canopy but planting alone is not enough.”