A new study has revealed a concerning trend in many U.S. cities: urban tree cover is in decline, and hardened surfaces are on the rise.
Twenty cities were assessed. By comparing aerial photographs taken over a period of five years, researchers tracked changes in the presence of trees, grass, and hardened surfaces—such as buildings, roadways, parking lots, and sidewalks.
The results were sobering. Seventeen of the 20 cities had statistically significant declines in tree cover. And in the face of shrinking green spaces, most cities saw increases in hardened surfaces.
After accounting for natural disasters, the cities with the steepest declines in tree cover were Houston, Texas and Albuquerque, New Mexico. Only one city – Syracuse, New York – showed a modest increase in urban tree coverage.
This is bad news, given the tangible benefits urban trees provide. Environmentally, they improve air quality, control storm water runoff, and help regulate temperatures. And socio-economically, tree-filled neighborhoods are linked to lower crime rates and higher property values.
“Tree cover is dropping about 20,000 acres per year, which equates to about 4 million trees nationally.”
David Nowak is a USDA Forester and lead author on the study…
“Is this a long term trend? We do not know. The question is if we know this trend is changing and moving downward, what do the cities want to do about that. And a lot of cities are establishing canopy goals to try and move canopy cover up to a certain level so they can have the sustained benefits for current and future generations.”
Citizens are among the most effective urban tree advocates. The USDA has compiled a suite of resources at www.itreetools.org.
Web Links
Dave Nowak, Baltimore Ecosystem Study/USDA Forest Service
http://search.lternet.edu/directory_view.php?personid=9672
Tree and Impervious Cover Change in U.S. Cities
http://journalistsresource.org/studies/government/municipal/tree-impervious-cover-change-us-cities/
Photo, taken on July 22, 2012, courtesy of Luke McGuff via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY, with partial support from the Field Day Foundation.