Urban Forests

May 2021

Wilderness may be more glamorous, but for the 80 percent of the United States population that lives in cities, urban forests are where we find our daily dose of nature. Northern Research Station scientists Dave Nowak and Eric Greenfield estimated that annual benefits derived from U.S. urban forests in terms of air pollution removal, carbon sequestration, and lowered building energy total $18.3 billion.

Managing a resource that contributes these and so many more benefits, including improving our health and our mood, takes science. In May, our web features introduce you to a scientist applying traditional research techniques to urban forests, research that established guidelines for urban tree monitoring, and a partnership that is working to bring elms back to the boulevards of America.

Environmental Education

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Featured Scientist

Nancy Falxa Sonti

Nancy Falxa SontiIn the world of forest science, plant ecophysiology is fundamental. The study of how plant physiology underlies ecological observations is sometimes perceived as an old-fashioned discipline, but Research Ecologist Nancy Falxa Sonti is applying it in a revolutionary context.

Based at the Northern Research Station’s Baltimore Field Station, Sonti is diving into tree fundamentals in a new landscape for plant ecophysiology – cities. She is one of a few people breaking ground in this new science subdivision, too. Sonti recently contributed to an urban ecology book with a discussion of how to incorporate urban tree health metrics and measurements such as urban tree growth, photosynthesis, respiration, sap flow, and other physiological traits in urban environmental research.

“Urban forests are a significant investment for cities, and they play a vital role in human health and wellbeing,” Sonti said. “The ability to quantify urban tree health and physiological function is something urban forest managers need as they make management decisions and plan for the sustainability of urban forests.”

Sonti believes that both urban forests and traditional forests would benefit from a better understanding of how they are alike and what contributes to their productivity, including soil conditions, air quality, the urban heat-island effect and nitrogen deposition. However, logistics in cities can make the research a lot more complicated, Sonti said. “In rural forests, you generally do not need to coordinate permissions with as many landowners as you do in the city,” she said.

A native New Yorker, Sonti has also spent time in California and Massachusetts, where she developed a love of the outdoors on family hiking and camping trips. An early biology class sparked her interest in plants, but she considered natural resources to be a personal passion rather than a potential career until she did an internship with the New York City Department of Parks & Recreation. “I hadn’t thought of natural resources as being something that I could do as a career and still live in the city, which I wanted to do,” Sonti said. “As an intern, I discovered that I could do the two things I wanted to do without leaving the city: serve my community and pursue environmental research.”

One of the things that has surprised her in her 10 years with the Northern Research Station has been how interested people are in the trees and natural resources surrounding them. “If you point out a tree that is 250 years old, people are just amazed,” Sonti said. “They want to know all about it. Things that are not necessarily surprising to those of us in research are fascinating to community members.”

More about Nancy Falxa Sonti >>

Featured Products

Urban Tree Monitoring: Field and Resource Guides

Cover images of Urban Tree Guides.Cities plant trees for the many values they provide, including beauty, shade, cleaner air, and flood control. Many municipal arborists and non-profit urban forestry leaders want to track the trees that they plant and manage, but variation in methods used presents challenges to making comparisons across cities and programs.  Two recent publications from the Northern Research Station and Pacific Southwest Research Station, a field guide and a resource guide, capture lessons learned to guide those who care for urban trees.

Monitoring the same individual trees over time produces longitudinal data, and such monitoring enables urban forest managers to analyze mortality and growth rates, as well as shifts in health. Long-term data can help managers keep trees healthy and protect city investments. While the USDA Forest Service and others have developed methods for longitudinal data collection in rural, natural forests proven and consistent guidance on monitoring urban trees was lacking, especially guidance for practitioner-driven monitoring.

“We wanted to adapt those best practices used in rural forests to the urban setting and offer tips and strategies for robust and careful long-term data collection,” said Lara Roman, research ecologist with the Northern Research Station and study co-lead.   

“Production of the two publications was a big collaborative project with 17 coauthors contributing,” said Roman. Natalie van Doorn of the Pacific Southwest Research Station and Roman led the effort with help from other crucial partners including other Forest Service researchers, university researchers (including faculty from University of Wisconsin, Stevens Point; University of Florida; and University of California, Berkeley) and some urban forestry professionals.

“While the urban tree monitoring field protocols were being drafted, we had many discussions with members of the Urban Tree Growth & Longevity Working Group, an affiliate of International Society of Arboriculture, and solicited feedback from urban forestry practitioners to ensure that our final products had optimal utility for those who care for urban trees,” said Roman.

The guides are currently being used in monitoring projects across many parts of the United States, from Pennsylvania and Massachusetts to California and Hawaii.

View the Urban Tree Monitoring Field Guide and the Resource Guide >>

Featured Partnership

Restoring Elms on America’s City Streets

Professor Tara Trammell and students Joshua Gainey (middle) and Max Huhn check on the health of an elm sapling planted in Newark, Delaware.  USDA Forest Service photo by Vince D'Amico.

American elm (Ulmus americana) was once widely distributed and common throughout the eastern United States, being a component of several major North American forest cover types and representing ‘Main Street America’ as a primary tree on many parkways and avenues. In the early 1900’s the Dutch Elm Disease (DED) fungal pathogens, Ophiostoma ulmi and O. novo-ulmi, were accidentally introduced into the United States and led to the widespread mortality of American elms growing in cities and forests alike, but things may be looking up. Through a partnership with researchers and municipalities, efforts are now underway to bring elms back to the boulevards of America.

For several decades, researchers have focused on identifying and breeding DED-tolerant varieties of American elm for restoration in natural forests and along riparian areas.  Scientists, including Northern Research Station researchers Leila Pinchot and Charlie Flower have cultivated more than 100 American elm selections to identify varieties that may be suitable for urban restoration plantings.

The Northern Research Station, University of Delaware, and several municipalities across the northeast and Midwest are testing how selective breeding of DED-tolerant elms will fare in an urban context. “Urban parks and street trees are often hit hard by invasive pests, pathogens, and pollution, leading to a higher degree of stress,” said Vince D’Amico, Northern Research Station Research Entomologist. “Our goal is to find a genotype of American Elm that is not only DED-tolerant but can also withstand harsh urban environments.”

D'Amico and Tara Trammell, John Bartram Assistant Professor of Urban Forestry at University of Delaware are collaborators on the reintroduction of American elms across a range of urban and suburban landscapes. In the fall of 2019, 135 DED-tolerant American elms were planted across 45 urban parks in Newark, DE; Philadelphia, PA; and in Columbus, OH. Researchers are continuing to monitor the survival and growth of these trees. “The hope is to identify American elm varieties and that can be used to enhance our city streets and parks once again,” said D’Amico.

“In addition to supporting improved public health and providing aesthetic benefits, American elms play an important ecological role within the urban environment,” said Trammell. “With this collaborative research underway, the future looks bright for these iconic trees.” 

More on Northern Research Station's elm restoration research >>

Last updated: 04/29/2021