Urban Tree Canopy Study
Assessing Urban Tree Canopy in the City of Atlanta
The City of Atlanta contracted researchers at the Center for Geographic Information Systems (CGIS) and the Center for Quality Growth and Regional Development (CQGRD) at Georgia Tech to quantify the existing Urban Tree Canopy in the City. Urban Tree Canopy (UTC) is defined as the layer of leaves, branches and stems of trees that cover the ground when viewed from above. The aim of the Atlanta UTC study is to help City decisionmakers and stakeholders better understand and manage their forest resources.
Why Urban Trees and Forests Are Important?
– Trees clean particulates from the air and soil, which helps decrease air and water pollution.
– Trees provide a stormwater management service by intercepting rainfall that would otherwise flow directly into water bodies and the drainage system, causing streambank erosion, and potentially overwhelming the stormwater system, especially in areas with combined storm and sanitary sewers.
– Trees provide habitat for native pollinators, migrating birds, and other important wildlife.
– Trees make neighborhoods and urban areas more livable by providing aesthetic, social, and psychological benefits for residents.
For many residents and visitors, Atlanta’s mature and vibrant urban tree canopy is its signature environmental feature.
Project at a Glance
The aim of the Atlanta UTC study is to help City decisionmakers and stakeholders better understand and manage their forest resources. Specific goals for this assessment were to (1) map urban tree canopy and other land cover across the City; (2) quantify tree cover for various geographies within the city (neighborhoods, NPUs, council districts, parks, zoning and land use, watersheds, stream buffers); (3) establish a baseline for measuring canopy change over time; (4) identify planting sites; and (5) summarize and make recommendations based on findings.
The research team identified and measured the existing tree canopy in the City of Atlanta through the analysis of high resolution, multi-spectral, “leaf-on” Quickbird satellite imagery obtained by the city in October 2008 from Digital Globe Inc. The analysis was accomplished utilizing both established and newly developed land cover classification techniques. The project team also developed coverage area data for two other general land classes: non-tree vegetation, and non-vegetation. Accuracy assessments were conducted to validate findings.
Summary of Findings
Urban Tree Canopy in AtlantaUrban tree canopy coverage varies significantly across Atlanta and is strongly related to zoning and land use, with the highest concentration of existing urban tree canopy located on residential property and the lowest in the downtown area and along transportation corridors. Significant concentrations of tree cover are also found along some of Atlanta’s stream corridors. The accompanying graphics show the extent and distribution of canopy across the City of Atlanta.
– The majority of tree canopy within Atlanta’s city limits (77%- 31,194 acres) is on single-family residential land. Single-family land makes up 60.8% of the city’s total land area.
Canopy Distribution Across the City
– Multi-family residential land contains the second highest amount of the city’s total canopy (8%), followed by industrial (6%); these categories make up 9.4 % and 11.8% of the city’s total land area, respectively.
– Parks contain approximately 4.9% (2,070 acres) of the city’s total tree canopy; park land makes up 4.5% of the city’s total area.
– 61% of all single-family residential land is tree covered.
Canopy Concentration within Selected Geographies
– 40% of all multi-family residential land is tree covered.
– 20% of all land zoned commercial is tree covered.
– Densely developed areas, such as downtown, surrounding neighborhoods, and former Atlanta Housing Authority developments have less than 5% tree cover.
– Several neighborhoods in the north and southwest have more than 70% canopy coverage, particularly those along Nancy Creek and Utoy Creek.
– Among parks over 50 acres in size, canopy coverage ranges from a low of 18% at Lakewood to a high of 94% at Cascade Springs Nature Preserve.
– Canopy coverage for sub-watersheds ranges from a low of 18% in Proctor Creek to a high of 72% in Long Island Creek — canopy in 100 foot stream buffers ranges from a high of 80% along North Utoy Creek to a low of 35% along Intrenchment Creek, with a City-wide average of 65% canopy coverage within 100-ft. stream buffers.
– Refine policies and set canopy goals to ensure that each area of the City receives the benefits of a healthy canopy and that the overall tree canopy is maintained and increased over time.
– Establish baseline tree cover information from which the City can measure and track progress.
– Establish an Urban Forestry Master Plan for achieving canopy goals.
– Educate the public about tree canopy in Atlanta through an online, interactive map accessible from the City’s website.
– Streamline the identification of potential planting locations based on derived ratios of UTC to Non-Tree Vegetation. Inform sustainability efforts and policy decisions related to climate, water and air quality, tree preservation and watershed protection.
– Establish a methodology to ensure comparability against results from future UTC studies.
The data generated by this research project will serve as a guide to Atlanta’s policy makers, a resource for its citizens, and a tool for planners and others concerned about Atlanta’s urban forest.