Since the 1990s, NYC Parks has worked with the US Forest Service on several ecosystem service studies quantifying the benefits of trees citywide. These studies played an important role in the creation of the successful MillionTreesNYC program, a goal to plant one million trees in New York City. More recently, the US Forest Service’s i-Tree Eco model was used to conduct an updated citywide assessment of forest structure and ecosystem services. In 2013, we established 296 11-m radius permanent plots, with a stratified random design by city borough. While this sampling strategy is useful for between-city comparisons or setting citywide management goals, urban forest managers also rely on data collected on the specific area being managed, much like their rural counterparts. Thus, from 2013 to 2014, the Natural Areas Conservancy worked with NYC Parks to establish 1,124 10-m radius permanent plots, using systematic random sampling, within forested areas on city parkland. These data were also analyzed using the i-Tree Eco model.
These studies tell two different stories about NYC’s urban forest structure and value. Based on the citywide study, there are roughly 7 million trees citywide, and the overall density is 36 trees per acre. Within forested areas, there are roughly 3.3 million trees, and the density is 459 trees per acre, indicating these areas have disproportionately more trees and provide greater ecosystem service benefits relative to their geographic size. The citywide species composition, across public and private land, also differs dramatically from the species composition within forested city parkland. Citywide, the most common species are mostly exotic species: Norway maple, northern white cedar, and tree of heaven. Within park forests, the most common species are predominantly native species: sweetgum, black cherry, and sassafras. These two analyses highlight how different sampling designs (e.g., sample size, areas sampled) influence our valuation and ecological understanding of the urban forest. While citywide assessments can provide valuable information on trees across all land uses, management decisions rely upon data collected from specific areas being managed. As ecosystem service models are continually refined and used for local decision-making and management, the availability of high-resolution datasets on specific areas can improve how management decisions are made.