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January 2008 Issue

Making the City a Greener Place
Technology can help us assess urban forests and plan for their future. 

By James L. Sipes, ASLA

Making the City a Greener Place Courtesy of Google Earth and the San Francisco Urban Mapping Program

I moved to Atlanta a little over a year ago, and one of the biggest surprises was how “green” the city is. In the parts of the city that have not succumbed to highways, parking lots, or skyscrapers, large-canopy trees provide valuable shade for those fortunate enough to live in those areas. I quickly found out, though, that all of the “green” was misleading. A study by the national conservation group American Forests revealed that more than 60 percent of the natural tree cover and vegetation in the Atlanta area has been lost since 1972.

Unfortunately, what is happening in Atlanta is similar to what we are seeing all across the country. Our urban trees are being eliminated at an alarming rate, and the potential impacts may be devastating. Researchers with American Forests discovered that every city they studied had at least a 30 percent decline in urban trees over the past 10 to 15 years.

Technology for Urban Forest Management

To effectively manage trees in urban areas, we need to have a basic understanding of what is there and how it is functioning. At the heart of virtually every street tree and urban forest project is GIS technology that helps locate, organize, analyze, and manage trees in urban areas.

GIS software works with both raster and vector data to varying degrees, with vector data being used for most urban forestry applications. Digital image analysis techniques are frequently used to provide estimates of canopy cover. A number of GIS programs use image-processing pattern recognition to automatically define tree canopies and plant massing. Digital image analysis techniques have the potential to provide precise estimates of canopy cover.

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