Market-Based Approaches toward the Development of Urban Forest Carbon Projects in the United States
The United States has observed unprecedented urban growth over the last few decades. Nowak et al. (2005) noted that between 1990 and 2000, the share of urban land area in the nation increased from 2.5% to 3.1%. Existing urban areas in the U.S. maintain average tree coverage of 27% (Nowak et al. 2001), and consist of millions of trees along streets and in parks, riparian buffers, and other public areas. Further, Walton and Nowak (2005) predicted that this urban area will continue to expand through 2050, eventually covering up to 8.1% of the country’s area. Some of the expected urban development will come at the expense of currently forested areas. This may further the scope of afforestation and subsequent reforestation as part of urban forest management. Increasing with the area of urban land is the geographical coverage of urban forests. Urban areas nationwide support more than 3.8 billion trees (Nowak et al. 2002), whereas as many as 70 billion trees are estimated to be growing in the urban and urbanizing areas throughout the nation (Bratkovich et al. 2008). A brief look at urban tree inventory data at individual state and city levels confirms that urban trees are a significant component of forest resources at local and regional levels. Table 1 presents canopy coverage and tree inventory data for five selected states and cities to illustrate the relative stocking of urban trees at individual state and municipal level (Nowak et al. 2001). Some of the states have smaller urban canopy coverage, but are densely stocked. Recent urban forest inventories also suggest that there is substantial variation of tree stocks among the United States cities, which ranges from roughly 15 trees per acre in Jersey City, New Jersey to about 113 trees per acre in Atlanta, Georgia (Nowak et al. 2010).