City Trees is a premier publication focused on urban + community forestry. In each issue, you’ll learn how to best manage the trees in your community and more!
Issue link: https://read.dmtmag.com/i/75614
Mapping Tree Canopy and Prioritizing Planting in NYC by Jarlath O'Neil-Dunne and Dexter H. Locke Advances in geospatial technology are standing of the resources they manage and helping them prioritize their tree planting efforts. In this article we will look at how new approaches to tree canopy mapping and tree planting prioritization are helping the City of New York meet its ambitious goal of planting and caring for one million new trees across New York City's five boroughs by 2017. giving urban foresters a more accurate under- Dubbed MillionTreesNYC, the initiative is a city- wide, public-private program led by the New York City Department of Parks & Recreation and New York Restoration Project in partnership with a num- ber of diverse public agencies, community-based groups, businesses and private property owners. MillionTreesNYC is just one of 127 initiatives in PlaNYC, the City's long-term sustainability plan which was launched by Mayor Bloomberg on Earth Day in 2007. Since PlaNYC's inception, more than 575,000 trees have been planted in the public right- of-way, in parks and natural areas, and on privately owned land. GIS analysis was key to quantifying New York City's exist- ing tree canopy and evaluating the feasibility of large- scale tree planting during the creation of PlaNYC. Geospatial technology continues to be central to the MillionTreesNYC planning and implementation effort. If you have visited the Big Apple, you might be asking yourself, "How much tree canopy does New York City have?" "Where are they going to plant all of those trees?" and "How will they prioritize where to plant them?" Let's first tackle the question of mapping New York City's existing tree canopy. Many readers are likely familiar with the Forest Service's Urban Tree Canopy (UTC) assessment protocols in which high- resolution satellite or aerial imagery is used to map tree canopy. A UTC assessment helps answer the first two questions, but in a city such as New York, images from aerial and satellite system have a key limitation: the inability to see through the shadows caused by large buildings. New York City's skyline is magnificent, but it causes havoc when it comes to mapping tree canopy! Fortunately a new technology known as LiDAR (Light Detection And Ranging) makes it possible to accu- rately map tree canopy even in downtown Manhattan. Unlike the typical imaging systems that rely on light reflected from objects, a LiDAR sensor provides its own light, in the form of a non-visible laser. Just like a flashlight allows you to find that lost sock in the corner of your dark closet, LiDAR allows us to find even newly planted trees hidden in the shadows of Manhattan's tallest buildings. What's also different about LiDAR is that it returns 3D data, allowing the heights of buildings, trees, and other features to be measured with centimeter-level accuracy. In the spring of 2010, just as the leaves were coming out, LiDAR data were acquired for New York City in support of a solar mapping project lead by the Center for Advanced Research of Spatial Information (CARSI) at the City University of New York's Hunter College. Figure 1. High-resolution aerial image over Manhattan: Although the image has a resolution of 6 inches, it is virtually impossible to tell what lies within the shadow (indicated by the arrow) of the multi-story building in the center. 30 Figure 2a. LiDAR 3D visualization of the same area in Figure 1, but from a different viewing angle. As LiDAR data is not affected by shadowing the features, trees in this case, within the building's shadow, are clearly visible City Trees