process. In Providence alone, urban trees prevent 31.5 million gallons of runoff annually [2]. Urban trees also actively absorb all of the pollutants (i.e. carbon monoxide, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide) monitored under the Clean Air Act of 1970. Trees take in air through their stomata, the pores in their leaves, to obtain the carbon dioxide necessary for photosynthesis [3]. In the process, they also absorb and retain pollutants, acting as air filters for the outdoors. Simultaneously, trees reduce building energy consumption. The water that evaporates from their leaves directly chills the air, while the shade they provide keeps buildings cooler in the summer [4]. Together, these impacts reduce pollution as less energy is made to power air conditioners. For the future health of our planet, urban forests will be instrumental. However, many cities still disregard their tree populations. Afflictions from Dutch Elm Disease, to Chestnut Blight, to the Emerald Ash Borer beetle have decimated the tree population of many
American cities over the course of the past century [4,5]. In the wake of devastating mass die-offs, little action is being taken to reinstate the amount of foliage lost. Presumably, the reason cities have not replaced their trees is the perceived economic burden this would entail. However, planting trees is actually economically favorable. The trees of Houston, TX, for instance, are valued at $1.3 billion for reducing stormwater, $300 million, for absorbing pollutants, $111.8 million for reducing air conditioning costs, and $13.9 million for reducing heating costs [6]. This is not an isolated phenomenon: here in Providence, every dollar spent on tree planting and maintenance returns $3.33 to the city each year “... in the form of energy savings, CO2 removal, air quality improvement, stormwater uptake, and aesthetic value” [2]. In total, this means Providence’s trees have an annual worth of just under three million dollars [2]. For a single city, these numbers are impressive. With an aggregate estimated value of 2.4 trillion dollars, the economic impact of all the urban forests in America is noteworthy, to say the least [7].
[1] Karvonen A. Politics of urban runoff. Cambridge, Mass.: MIT Press; 2011 [2] Still D. [Internet]. 1st ed. Providence: State of Providence; 2008 [cited 18 October 2016]. Available from: https://www.providenceri.com/ sites/default/files/file/Parks_and_Recreation/Providence_Urban_Forest_as_of_2008.pdf [3] Nowak D, Hirabayashi S, Bodine A, Greenfield E. [Internet]. 1st ed. 2014 [cited 17 October 2016]. Available from: http://www.fs.fed.us/ nrs/pubs/jrnl/2014/nrs_2014_nowak_001.pdf [4] Still D. [Internet]. 1st ed. Providence, RI: City of Providence; 2016 [cited 17 October 2016]. Available from: http://www.providenceri. com/efile/5424 [5] Anagnostakis S. Revitalization of the Majestic Chestnut: Chestnut Blight Disease [Internet]. Apsnet.org. 2016 [cited 29 October 2016]. Available from: http://www.apsnet.org/publications/apsnetfeatures/ Pages/ChestnutBlightDisease.aspx
Cities, in retrospect, lack a valid economic motive for continually ignoring their trees. Given this reality, it is likely that city leaders are simply unaware of the value of trees and as a result do not prioritize their presence. Even though the significance of the urban forest is overlooked, there is some evidence that the social value ascribed to trees is on the rise. In fact, Providence pioneered this movement. From the 1950s to 1980s, landscape architect Mary Elizabeth Sharpe led large scale tree planting efforts in the city, in an attempt to restore the urban canopy to its former size. Her legacy continues today; there is a plan to increase Providence’s tree coverage by 30% by the year 2020, for example [8,9]. Other cities have followed suit, such as New York City, which accomplished it ambitious goal of adding one million trees to the city in November 2015 [10]. Evidently, cities have started to catch on to how important the urban forest really is. As both a lover of trees and a proponent of practical environmental programs, I can only hope this trend continues.
[6] Foster J, Lowe A, Winkelman S. The Value of Green Infrastructure for Urban Climate Adaptation [Internet]. 1st ed. 2011 [cited 20 October 2016]. Available from: http://www.amwa.net/galleries/climate-change/ Green_Infrastructure_FINAL.pdf [7] Nowak D, Crane D, Dwyer J. Compensatory value of urban trees in the United States [Internet]. 1st ed. 2002 [cited 21 October 2016]. Available from: http://www.nrs.fs.fed.us/pubs/jrnl/2002/ne_2002_nowak_003.pdf [8] Rhode Island Heritage Hall of Fame: Mary Elizabeth Sharpe, Inducted 2001 [Internet]. Riheritagehalloffame.org. 2016 [cited 19 October 2016]. Available from: http://www.riheritagehalloffame.org/inductees_detail. cfm?iid=440 [9] Trees 2020 [Internet]. Trees2020.org. 2016 [cited 21 October 2016]. Available from: http://trees2020.org/ [10] MillionTrees NYC [Internet]. Milliontreesnyc.org. 2016 [cited 19 October 2016]. Available from: http://milliontreesnyc.org/html/home/home.shtml
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