A new study published in Nature Cities (October 3, 2025) warns that Boston’s oak trees contain far more “bad” microbes, like pathogens and plant decomposers, than beneficial ones. According to the study’s lead author Kathryn Atherton (a former Boston University Ph.D. student in the Urban Biogeoscience and Environmental Health program), the trees are succumbing to city stressors like heat, drought, and atmospheric aerosol deposition (pollution). The impacts have health consequences for trees—and humans.
While trees in Boston grow four times as fast as their rural brethren, they also die twice as quickly, according to previous research. By understanding what’s different about urban tree microbiomes, Atherton hopes to find ways to help Boston’s tree canopy thrive.
“Living in the city … is basically a nightmare situation for a tree,” said Jennifer Bhatnagar, associate biology professor at Boston University and the paper’s senior author. She said the microbiomes of city trees have shifted in a way “that is not beneficial for the tree, necessarily.”
That shift may not be good for humans, either. Researchers observed animal and human pathogens associated with high levels of air pollution on urban trees. They also found bacteria that produce greenhouse gases like nitrous oxide, potentially limiting the ability of trees to absorb carbon dioxide from the atmosphere. City trees also have fewer microbes that eat methane, another potent greenhouse gas.
“Urbanization reduces overall tree microbiome diversity, particularly among non-pathogenic microbes, potentially diminishing the ecological and health benefits of environmental microbiomes in cities.”
Read “Disruption of the Oak Tree Microbiome with Urbanization” in full.