Tree-Associated Fungal and Bacterial Communities at Harvard Forest 2021

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. Our research aims to characterize the belowground variables and microbial community composition that might explain the differences in growth and mortality rates observed between urban and rural trees. In 2021, soil, leaf, and root samples were taken from 25 trees in Harvard Forest to use as a rural comparison to Boston’s street trees and trees in other forests along an urban-to-rural gradient from Boston into Western Massachusetts. At each tree, three 12” deep, 2.4-centimeter radius soil cores were taken within the drip line, and soil cores were divided into the top 6” and lower 6” of soil. Fine roots were picked from each soil core. Six leaf samples were taken from the mid-canopy of each tree, where possible. Soil variables including temperature, moisture, percent organic matter, soluble nitrogen availability, bulk density, and root biomass were measured. Thus far, we have found that urban trees have fewer roots than Harvard Forest trees (F1,252) = 10.88, p = 0.0011), and that urban trees establish more root biomass deeper into the soil than Harvard Forest trees (p = 4.84e-5).