COS 315-5 - Urban trees grow faster when planted further from industrial zones

Thursday, August 10, 2023

4:30 PM – 4:45 PM PDT

Location: E146

Presenting Author(s)

KA

Kathryn F. Atherton

Bioinformatics PhD Candidate
Boston University
Boston, Massachusetts, United States

Coauthor(s)

IF

Isabelle Frenette

Biology Undergraduate Research Assistant
Boston University, United States
DH

David Heaton

Biology Undergraduate Research Assistant
Boston University, United States
Chikae Tatsumi

Postdoctoral Fellow
Boston University
Boston, Massachusetts, United States
IS

Ian Smith

Earth & Environment PhD Candidate
Boston University, United States
LH

Lucy R. Hutyra

Professor of Earth & Environment
Boston University, United States
JB

Jennifer M. Bhatnagar

Associate Professor of Biology
Boston University Department of Biology, United States

Abstract: Cities are investing in tree-planting initiatives to protect their citizens from climate change-related heat and pollution exposure, yet Boston’s street trees are growing nearly four times as fast and dying twice as young as Massachusetts’ rural forest trees. We hypothesized that distance from industrial zones and soil factors such as high temperature and pH would explain a portion of the observed growth and death trends. To test this hypothesis, we collected soils from 37 oak trees planted in street tree pits in seven different Boston neighborhoods and 14 rural oak trees within the Harvard Forest’s Biomass Inventory plots. We measured the size, or diameter at breast height (DBH), of each tree and calculated its average growth rate over the past decade, and collected soil cores to measure temperature, pH, moisture, organic matter content, bulk density, and root biomass underneath each tree. We also used GIS software to determine each street tree’s distance from an industrial zone. Our models of tree growth were able to replicate the previous observation that urban trees grow faster than rural trees (F(1, 202) = 62.14, p = 1.96e-13). We found that street tree size was correlated with distance from industrial zones (β = 4.92e-5, t(3337) = 4.30, p = 1.73e-5), suggesting that trees closer to industrial zones are younger and have more turnover than trees further from industrial zones. Additionally, we found that soils closer to industrial zones had a significantly higher pH (β = -0.6150, t(183) = -4.69, p = 5.32e-6) and higher temperature (β = -2.3663, t(177) = -6.03, p = 9.56e-9) than trees farther from industrial zones. Our results indicate that soil in proximity to urban industry is harsher for trees than soil on streets that are further from industry in the city. Neighborhoods closer to industrial zones often are neighborhoods that need more trees, so, it is imperative that tree-planting initiatives are implemented alongside other actions, such as painting concrete surfaces white to cool the pits that trees are planted in or using organic compost rather than synthetic fertilizer to lower the soil pH. Though changes in soil properties did not directly explain tree mortality, they may make the soil microbiome less beneficial for trees, selecting for more copiotrophic taxa. As such, future research will investigate how the leaf, root, and soil microbiomes are related to tree growth and mortality rates.