Why Do Urban Trees Grow Faster than Rural Ones?
W. M. Keck Foundation to support BU project to delve into the mystery of city tree survival strategies

Forest microbial ecologist Jennifer Bhatnagar (center) will use funding from the W. M. Keck Foundation to test whether urban trees have shifted their “survival strategies from belowground roots to aboveground canopies.” She’ll be joined in the work by BU researchers Pamela Templer (left), Lucy Hutyra (right), and Jeffrey Geddes (not pictured).
Why Do Urban Trees Grow Faster than Rural Ones?
W. M. Keck Foundation to support BU project to delve into the mystery of city tree survival strategies
A dense, lush forest would seem the ideal location for trees to grow—pristine, free from pollution pumped out by vehicles and industry. But a few years back, Boston University researchers discovered an intriguing quirk of nature: city trees grow significantly faster than their rural counterparts. Now, they’re trying to understand why. And their effort has won national recognition with backing from the W. M. Keck Foundation, which is giving $1 million to help fund their research.
Established in 1954, the Los Angeles–based philanthropic organization supports science, engineering, and medical research with a focus on novel proposals that strive to break new ground. The latest BU project is being led by forest microbial ecologist Jennifer Bhatnagar, a College of Arts & Sciences associate professor of biology and director of the BU Biogeoscience Program. She and her colleagues hope to use a better understanding of how urban trees adapt to sometimes harsh conditions to support preservation initiatives.
According to Stan Sclaroff, dean of CAS, the award is “testament to the strength of our innovative and impactful research program in urban biogeosciences. The support from the W. M. Keck Foundation will enable Jenny and her collaborators to delve deeper into the mysteries of urban tree survival strategies, which could have far-reaching benefits in enhancing urban environments and improving quality of life for city dwellers.”

Bhatnagar will be joined on the project by CAS researchers Jeffrey Geddes, an associate professor of Earth and environment, Lucy Hutyra, a distinguished professor and chair of Earth and environment, and Pamela Templer, a distinguished professor and chair of biology. The Keck grant will be used to fund field and lab supplies, sample analyses, and salaries for postdoctoral scholars and graduate students. Previous Keck awardees at BU include physicist Plamen Ch. Ivanov and biomedical engineer Ahmad (Mo) Khalil. The foundation, which was established by Superior Oil Company founder William Myron Keck, is one of the nation’s largest philanthropic organizations and also supports undergraduate education as well as community enrichment programs in Southern California.
The Brink spoke with Bhatnagar to learn more about the survival instincts of urban trees, the societal importance of preservation efforts, and why Keck’s recognition matters.
Q&A
with Jennifer Bhatnagar
The Brink: What’s the goal of your project and how will you be conducting your study?
Bhatnagar: Recently, my colleagues, Lucy Hutyra and Pamela Templer, discovered that urban trees grow four times faster than rural trees, despite a multitude of environmental stressors in cities and the loss of typical belowground mechanisms for trees to acquire nutrients, tolerate stress, and gain protection from pathogens. The goal of our project is to understand exactly how it is that trees grow faster in cities. We will test the hypothesis that urban trees operate by a different “rule of life” than rural trees, shifting their survival strategies from belowground roots to aboveground canopies, taking advantage of aboveground atmospheric pollution as a source of nutrients, water, and stress protection to support faster tree growth. We are applying a combination of field-based nitrogen, water, and atmospheric chemistry measurements, plant and microbial biochemical analyses, plant surface microscopy, and air pollution manipulation experiments to trees across a recently established, model urban-to-rural tree gradient in Massachusetts.
The Brink: Your project is titled Rules of Life in the Urban Biome. What is the urban biome?
Bhatnagar: The urban biome is the environment of an urban area, defined by population size, amount of man-made impervious surface area, or proximity to a city center. It includes the collection of all life-forms in urban areas: plants, animals, humans, and microorganisms, as well as the climate and other geological and physical factors that make up the environment in an area.
The Brink: What will this support enable you to do that maybe you couldn’t do without it?
Bhatnagar: The Keck award allows us to explore potentially ludicrous ideas—for example, that trees use their leaves instead of their roots to absorb nutrients and leverage pollutants as a form of stress tolerance—and learn something of the truth about how plants adjust to survive in an environment created exclusively for humans. Proposing a new rule of life for urban trees is inherently risky, so likely would not have been funded by other granting agencies. Nutrient and water absorption by tree canopies has been demonstrated by other types of ecosystems—tropical forests, coastal fog ecosystems, high elevation spruce forests—but has never been explored in urban environments.
The concept of particulate matter reducing leaf-level [ozone] damage has also never been brought up before in the scientific literature. However, it is possible that these ways of life are expanding worldwide, with increasing levels of atmospheric pollution deposition in places where humans are colliding with the natural world. Quantifying the sources of water and nutrients for trees, as well as the metabolism of pollutants, are difficult tasks, requiring a diversity of techniques, including the use of stable isotopes in the lab and in a field setting. The Keck award provides the funds needed to accomplish this on a regional scale, across hundreds of trees, to establish whether urban and rural trees differ in their life strategies.
The Brink: The Keck Foundation’s goal is to support science that could “create far-reaching benefits for humanity” and “add to our understanding of the world.” How might your project do this?
Trees in urban areas provide multiple ecosystem services—including heat mitigation, stormwater management, habitat resources for native pollinators, air pollutant reduction, carbon sequestration, and improvement of mental and physical health outcomes of citizens—so the societal value of an individual tree is exponentially higher in a city than it is in pristine, rural habitats. As a consequence, cities worldwide are investing millions of dollars in greening initiatives to increase tree canopy cover and preserve urban forest land; greening initiatives are ongoing in at least 100 cities around the world, with a global goal of including 1,000 cities by 2030. Understanding the rules of life for urban trees is increasingly critical to support these initiatives.
The Brink: Keck also says that projects it supports are “novel in their approach, question the prevailing paradigm, or have the potential to break open new territory in their field.” What’s different about your project?
The urban biome is an extreme, human-created environment that is expanding across land surfaces at an alarming rate: by 2050, over 20 percent (118,300 square kilometers) of US forest land is projected to be subsumed by urban land development. The data we generate on how trees cope with or exploit this environment has the potential to completely redefine our understanding of how organisms acclimate to this rapid change in our world. In challenging the historical paradigm of how trees survive on Earth, our project could catalyze conceptual shifts in a diversity of fields, including botany, ecosystem ecology, forest science, biogeochemistry, microbiology, global change biology, and biodiversity science.
The Brink: How does this project fit with your broader work and research goals?
As a collaborative group, my co-principal investigators and I are deeply interested in understanding how the environment works—from belowground through the land and atmosphere—and identifying potential solutions for any negative effects human activity has on the environment. This project will provide insight into the fundamental principles of plant life in urban areas, which is foundational to managing and protecting plants living under stress. My own research is driven by a lifelong fascination with understanding Earth’s most complex biological systems: my main expertise is in understanding the activity of Earth’s unseeable organisms and microorganisms, and how that activity scales up to impact global processes of plant productivity, nutrient cycling, and carbon sequestration.
The Brink: What message or advice would you have for students or early-career researchers reading about this award—and your work—and hoping to follow in your footsteps?
My main advice to early-career researchers, based on my experience with this award and others, is to not give up on yourself. If you love research, don’t let someone else’s rejection of your ideas or your research products stop you from trying again. I have applied for many research grants to study the urban biome in recent years, all of which were rejected. The silver lining to those experiences is that I was left with lots of text describing my ideas, as well as more time to mull over ideas that might have been less than great—and make them greater for this proposal. I recently heard an interview where someone said they love criticism—if criticism were a food, they would eat it all the time. I like this idea, because I have found that there is something to be learned from just about every piece of constructive criticism of my research. It can be painful to acknowledge that what you’ve thought or done isn’t great, but it is a great way to figure out what you can do next.
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