The 2001 National Land Cover Data (NLCD) program includes an estimate of tree canopy density for the entire United States. The data estimates the percent of tree canopy found in each 30 meter pixel derived from Landsat satellite images. These data provide opportunities for communities to assess the extent of their tree canopy cover or to compare their canopy cover with other communities across states, regions and the country. While this information is extremely valuable, it only represents a snapshot of a single point in time. Communities need to be able to track trends in canopy change.
The USGS has made all Landsat images available to the public for free. In addition, the methodology for producing land cover, tree canopy and impervious surface products is publicly available. Now anyone with image processing capabilities can produce trend data products that can be used to track canopy density change.
From 1991 Landsat data, we developed a second set of canopy information for the southeastern United States. This includes tree canopy coverage for Mississippi, Alabama, Georgia, Northern Florida, South Carolina, North Carolina, Tennessee, Kentucky and most of Virginia. These data allow communities across the southeastern United States to begin to evaluate the trends in community tree canopy cover. The information can be used to determine the success of a number of urban forest programs from the success of tree ordinances to planting programs. For the first time, these trends data are consistent across a region; therefore, communities can compare their results and benchmark their programs. These data can be used in a number of modeling applications providing information on ecosystem services (storm water management, air quality, carbon sequestration and energy efficiency) to assess the value of tree canopy in providing these services and how they change over time.
The data are spatially referenced and therefore can be integrated with other spatial information such as demographic information from the United States Census Bureau or local property tax, to public health information from Centers for Disease Control (CDC). This allows users to evaluate how tree canopy might better serve the community by increasing property values, providing recreational opportunities, influencing public health and an array of other quality of life indicators. The only limit to the types of analysis is the imagination of the user.
The datasets provided include GIS data for each state for 1991 and 2001. The databases also include state, county, and city boundaries. The excel spreadsheets provide tree canopy calculations for each county and city in each state for 1991 and 2001. The data includes tree canopy acres and the percent canopy for each political unit. There is an accompanying tutorial that shows users how to work with the tree canopy data using ArcGIS software and Spatial Analyst software. The interactive map allows users to view the results of the data.