Urban forests have acquired increased relevance, not only as places for recreation, but also as sinks for anthropogenic atmospheric CO2. Quantifications of ecosystem services have already been produced for the urban forests of several major cities in the U.S., such as New York, San Diego, and Atlanta (American Forests, 2008). However, even though Memphis has a significant number of parks, relatively little has been done to assess and quantify their ecosystem services. To aid in this process, American Forests (2008) has developed a GIS software system called CITYgreen which quantifies urban ecosystem benefits such as stormwater management, clean air, and energy savings. CITYgreen studies have led to significant increases in investments in urban tree programs and research in other cities. In other words, when tree benefits are scientifically demonstrated, trees effectively compete for political and economic support. This study quantified the amount of carbon sequestered and stored by Memphis urban parks, using CITYgreen. We used aerial images from Google Earth with the software program to measure the canopy coverage of 35 parks in Memphis (71% of the total park area of Memphis).
According to the model, the total carbon stored by the urban parks is 116,789 tons and 5,840 tons of carbon are sequestered every year. We additionally surveyed two parks to compare field-based measurements of tree carbon with those estimated by the model. Field data were collected by measuring the diameter at breast height of every tree and the amount carbon stored and sequestered were calculated using allometric equations (Ter-Mikaelian and Korzukhin, 1997). Field-based calculations of carbon values were at least 20% higher than those estimated by the model. The CITYgreen software provides an important overall evaluation of greenspace benefits; however, the model should be complemented with field-collected data to obtain a more accurate quantification of urban parks ecosystem benefits.