Shrinking Forest Canopies and Urban Heat Islands

By Lucia Shuff-Heck
October 27, 2020

In the latest issue of the Biophilic Cities Journal, Vol. 3 No. 2, Taking Stock: The First Step to Creating Healthier Cities With Trees provided an overview of tools to assist cities in improving tree canopy, targeting areas of the city that need it most. The article by David Novak, a senior scientist and i-Tree Team Leader with the USDA Forest Service, outlines some of the characteristics of tree canopies in cities, including the problems they are facing.

As urban populations grow, and cities expand, tree populations continue to decline. An important aspect of forest management is data collection, something the USDA hopes to encourage with tools such as I-Tree, an analytical tool that provides information on urban forests by quantifying the structure and value of local forests. Through I-Tree, cities can accurately assess tree canopies by parcel and identify threats to the health of trees and forests.

Forest management tools like I-Tree also have the potential to help cities identify insufficient tree canopy in underserved neighborhoods. Unequal distribution of nature across cities is part of a larger trend, in the United States and across the globe, that threatens cities and their residents. One of the detrimental effects of inadequate green space is the urban heat island effect, a challenge that only grows more severe as climate change stokes increasingly higher temperatures in hot summer months.

A recent article in the New York Times highlights the staggering disparities within "urban heat islands," noting that temperatures can vary by as much as 20 degrees across neighborhoods in the same city. Of the temperatures recorded, the lowest were in forested neighborhoods, and the highest in industrialized areas, downtowns, and areas with a high proportion of asphalt surfaces and little to no tree cover. In multiple cities, high temperature districts aligned with lower-income neighborhoods, predominantly communities of color, while the comparatively low temperature districts were mostly white and higher-income.

Research supports these findings. A study of 108 urban areas in the United States identifies the role of historically racist housing policies as a factor in the variances of intra-urban heat. Approximately 94% of areas studied demonstrate higher land surface temperatures in redlined areas compared to non-redlined areas, increasing the vulnerability of these neighborhoods to extreme heat events.

In order to address disparities like these, services like I-Tree are essential, and can allow city officials to more easily identify areas that suffer from diminished tree canopies. Urban Forests: Nature as a Resource, a Biophilic Cities white paper by Jess Stevens, further clarifies the benefits of urban forests, and outlines steps to developing a Green Infrastructure Plan. With targeted plans, like those in Portland, or Melbourne, cities can more equitably address the need for urban greenery in all communities.

Lucia Shuff-Heck is the Communications Coordinator for Biophilic Cities, and an undergraduate in the Global Sustainability program at the University of Virginia.