urban trees — Burghardt Lab

Impacts of historical housing policy on urban tree communities

Funding: NSF and USDA

People involved: Meghan Avolio at Johns Hopkins University; Morgan Grove, Dexter Locke, and Nancy Sonti at the USDA Forest Service; Christopher Swan at UMBC

Below is an excerpt from UMD’s College of Mathematical and Natural Sciences news release. The full publication is open access and can be found here.

In the study, researchers analyzed street trees in 36 Baltimore neighborhoods that were once classified by the Home Owners’ Loan Corporation (HOLC), a New Deal program intended to expand homeownership. Infamously, HOLC classified and color-coded neighborhoods by perceived mortgage risk—green was designated as “best,” while red was deemed “hazardous.”
Often, the criteria used to classify neighborhoods was explicitly discriminatory; neighborhoods with high populations of racial and religious minorities as well as immigrants were more likely to be “redlined.” As a result, residents in those areas often experienced lower property values, resource investment by cities and wealth accumulation decades into the future.
“We found that previously redlined neighborhoods had consistently lower street tree diversity and were much less likely to have larger, older trees on a site,” said Karin Burghardt, lead author of the study and an assistant professor of entomology at UMD. “This is important because the differences in tree size and diversity affect the natural ecological services provided by trees—ultimately impacting the quality of life for residents living nearby.”
The team discovered that green, low-risk neighborhoods were nine times more likely to have larger and older trees present than red, high-risk neighborhoods. Additionally, trees found in green neighborhoods were significantly more diverse containing more types of trees than in red neighborhoods. The researchers found that present-day street trees in Baltimore contained signatures of the 1937 HOLC loan risk classifications that had been based on racially discriminatory criteria.

Tree size distribution, community composition, reordering, and turnover of tree communities by neighborhood HOLC grade. (a) Smoothed kernel density estimate of tree sizes (dbh) for each HOLC grade. The dotted lines indicate the dbh cutoffs used to classify “small” and “large” tree designations used for the “old” versus “young” community comparisons. (b) Nonmetric multidimensional scaling (NMDS) of large and small tree communities. Ellipse denotes the 95% confidence interval for that distribution of points. (c) Reordering and species turnover of large and small trees among HOLC grades. Significant differences (p < 0.05) are denoted by letters.

Selection in the city: understanding the roles of natural and domestic selection in shaping the function and sustainability of urban forests

Funding: USDA

People involved: Eva Perry, Meghan Avolio at Johns Hopkins University; Morgan Grove, Dexter Locke, and Nancy Sonti at the USDA Forest Service.

Trees are long-lived and provide key health benefits and ecosystem services to city residents leading to world-wide efforts to increase greenspace and tree cover in cities. Trees planted in cities face temperature increases (urban heat island effects and climate change) while simultaneously experiencing greater incidences of insect pest outbreaks. Are the trees we are currently planting in our urban forests optimized to withstand these stressors or will the use of genetically identical cultivars and clones selected for traits that humans prefer such as flower number and color decrease the adaptability of urban forests? We are examining whether domestic selection (breeding or nursery/consumer choices) of urban maple trees, Acer spp., changes the genetic structure of remnant urban forests and their resilience and resistance to climate change and insect pests.