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Urban Forests and Human Health

March 2015

While our own efforts to be healthy sometimes falter (this winter has required a certain amount of comfort food, after all), trees are more steadfast. Research is revealing that trees contribute to human health in a variety of ways, including removing air pollution, which saves hundreds of lives and prevents acute respiratory symptoms for thousands of people every year. The benefits extend beyond physical health; natural resources are a mechanism for individual and collective recovery from disaster.

This month, we feature a scientist, research, a product and a partnership that illustrate how trees benefit human health.

Environmental Education Links

Start exploring the benefits of your school’s or neighborhood’s trees with iTree Learning Lab (5 mb pdf - You may download a free pdf reader from Adobe), a tree inventory and benefits activity for grades 9-12. Once you’ve completed your tree inventory, you can visit to calculate the overall benefits of each individual tree, including information on air quality and carbon dioxide.

Look beyond trees and human health with ClimateChange LIVE’s Educator Toolkit. Learn how our changing climate affects human health issues such as vector-borne diseases, extreme weather events, and ocean acidification, and more.

Featured Scientist

Dave Nowak

Dave Nowak.  Photo used with permission by Kelsey Nowak.

Dave Nowak, a research forester in Syracuse, N.Y., has devoted his career to demonstrating how billions of urban trees contribute to human health and well-being.
Nowak has been motivated by a desire to do something different to improve human health and the environment in cities. Urban forests had attracted little scientific attention when Nowak began his career, so much of his early research focused on developing methods and tools to analyze urban forests. One of those tools is i-Tree (, an innovative and versatile suite of free software and web-based tools that Nowak developed in collaboration with private industry, universities and non-governmental organizations.

“Scientific papers are important, but not the most useful end product to help managers,” said Nowak, the author of more than 200 articles. “It’s essential to use the science behind those papers to develop tools that people can use to design better landscapes and improve quality of life.”

Nowak’s recent research has focused on quantifying the role urban forests play in reducing air pollution. A study Nowak and others published last year revealed that trees in the conterminous United States are saving more than 850 human lives a year and preventing 670,000 incidences of acute respiratory symptoms.

While some tree benefits, such as shade and aesthetics are more readily sensed by residents, their invisible benefits – such as reducing air pollution and ultraviolet rays – are often less appreciated. “Urban forests provide much more value than people realize,” Nowak said. 

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Featured Product

Environmental Justice - A long view of polluting industry and environmental justice in Baltimore

Publication provides long view on Baltimore’s history with pollution and environmental justice. Photo by Geoffrey Buckley, Ohio University

Environmental justice research often finds a pattern of polluting industries located in areas populated by people of color. At the larger scale, Baltimore City fits that pattern – people of color constitute a majority of the population, and the city has greater levels of toxic pollutants than any of the surrounding counties in Maryland. However, at finer spatial scales of data, an unexpected pattern emerges: most of the toxic releasing facilities recorded in the U.S. Environmental Protection Agency’s Toxics Release Inventory are found in or near white rather than black neighborhoods.

That data does not suggest a positive history of housing policies for the city’s people of color, in fact just the opposite. In the past, white privilege meant close access to employment in factories; the legacy of that past privilege is now a disproportionately high concentration of polluting facilities in white neighborhoods.

Morgan Grove, a scientist in the Station’s Baltimore Urban Field Station, and partners mapped the historical distribution of polluting industries in Baltimore and compared those distributions to nearby social and housing characteristics. Their research showed that the burden of pollution has been spread unevenly in Baltimore for a long time. From 1960 to 2010, the density of polluting facilities has remained high in neighborhoods with low educational attainment.

As Baltimore City contemplates a sustainable future, an understanding of long-term environmental justice patterns becomes essential, according to Grove. 

“Creating a sustainable Baltimore has the potential to improve the lives of all Baltimoreans,” Grove said.
“Addressing a long pattern of inequity is part of making the city sustainable; sustainability is neither credible nor operational without specific attention to justice.”

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Featured Research

Landscapes of Resilience

The Memorial of Remembrance at the Shrine of St. Joseph in Stirling, N.J., is a landscape of resilience. Photo credit: Living Memorials Project National RegistryDisaster, natural or otherwise, personal or collective, seems to drive us toward nature. In a variety of settings, scientists in the Northern Research Station’s New York City Urban Field Station are studying “landscapes of resilience” and the myriad ways that nature can become a mechanism of recovery.

After the attacks on September 11, 2001, scientists Erika Svendsen and Lindsay Campbell began a long-term study of the role of trees and open space stewardship in collective resilience. The Living Memorials Project documented and investigated more than 700 memorials nationwide; this year, Svendsen and Campbell will revisit that work to investigate if and where stewardship efforts have persisted and how collective stewardship has affected the people engaged in it.

New York City Urban Field Station scientists are continuing this line of research in a project called “Landscapes of Resilience: Understanding the Creation and Stewardship of Open Spaces Sacred Places.” The research centers on Joplin, Mo., where an EF5 tornado struck in May 2011, and Rockaway Peninsula in New York City, one of the areas devastated by Hurricane Sandy in October 2012.

Working as part of a multi-disciplinary team that includes Cornell University, Drury University, the City of Joplin, Forest ReLeaf of Missouri, and TILL Design, scientists are exploring how urban green spaces promote individual and community resilience. The research is one of six projects the TKF Foundation funded as part of its 2013 National Nature Sacred Awards.

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Featured Partnership

Davey Institute and i-Tree

A partnership helps quantify the value of urban forests. Photo credit: Morton Arboretum, used with permission.

From Fond du Lac, Wis., to London, England, i-Tree is helping communities get to know their trees.

Launched in 2006, i-Tree is a state-of-the art, peer-reviewed software suite that cities of all sizes can use to quantify the structure of community trees and the environmental services that trees provide. “The ability to put a value on our urban forests provides not only environmental awareness, but promotes community stewardship and better decision making,” according to i-Tree co-creator Scott Maco of Davey Tree Expert Company. “For many, carrying out an i-Tree analysis is no longer an option. Rather, it is now considered the first step in understanding the value of our community tree resource and developing a plan for cost-effective management.”

Initially, i-Tree creators expected interest in the software to be limited to city foresters in the United States, according to Dave Nowak, a research forester with the Northern Research Station and an i-Tree co-creator. With continual updates and expanded capabilities, the software has attracted new users, including teachers, researchers, non-government organizations and consultants. Most of i-Tree’s 30,000-plus users are in the United States, but the software is now widely used all over the world, having users in such diverse places as Brazil, India, Russia and Australia – and over 100 countries in-between.

i-Tree has been developed, supported and distributed through a consortium of partners including the U.S. Forest Service, Davey Tree Expert Company, National Arbor Day Foundation, Society of Municipal Arborists, International Society of Arboriculture,  Casey Trees, and SUNY College of Environmental Science and Forestry. All of i-Tree’s programs are available free-of-charge at

“The partnership among all of the groups – along with feedback from user groups – has been fantastic,” said Nowak. “It has led to new ideas, tools and expanded usage and impacts across the globe.”

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