Emerald Ash Borer: Its Effects on Urban Forestry, Temperature, and Equity

Emerald Ash Borer (EAB), an invasive insect first identified in Michigan in 2002, has killed tens of millions of ash trees across the country, especially in Midwestern cities. EAB arrived in the City of Chicago in 2007, and the response to its infestation of street trees was led by the Department of Streets and Sanitation. They combated the infestation by protecting some trees with stem injections of insecticide and by culling young and non-specimen trees. The patterns of tree removal and treatment can have profound impacts on the provisioning of ecosystem services. Trees are one of the best tools to mitigate the urban heat island effect, and the extensive loss of tree canopy may affect surface temperature. The goal of this study was to investigate the local climactic effects of canopy loss due to EAB, as well as to explore whether the response to it was influenced by socio-economic or land use factors. To do this, land surface temperature generated from Landsat imagery from 2007 to 2017 was combined with records of ash treatment and removal from the Department of Streets and Sanitation, LiDAR-derived canopy change, and parcel-scale land use data. These datasets were aggregated to census tracts across each year of temperature data and ash treatments and removals. We found that EAB and canopy change can have a significant effect on the local surface temperature, that Chicago currently lacks an equitable distribution of street trees, and that under-resourced communities experience higher surface temperatures. It is important to understand how the loss of urban street trees due to EAB has impacted local climates within cities, especially as climate change results in more severe heat waves. This is particularly important in Chicago, where a heatwave in 1995 killed over 500 people—the majority of whom were low-income and/or minority residents. Recognizing this, there are increasing efforts to reduce the inequity of tree plantings in Chicago. The results of this study can help guide work to reduce urban heat island effect and protect the city's most vulnerable residents.