Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Data

Data Collection Methodology: The data presented here are from the National Land Cover Dataset (NLCD); see the technical note for the national extent indicator for a full description.

Data Manipulation: The U.S. Geological Survey (USGS) Earth Resources Observations Systems Data Center aggregated data from the NLCD into squares 1 km on a side (approximately 1000 30-meter by 30-meter “pixels”). Each of these larger squares was analyzed to determine its land cover composition; 1-km squares in which more than 50% of the pixels were croplands were included within the “farmland landscape.” In addition, a “buffer” equivalent to a single 1-km square was added to the edge of the farmland landscape defined above, in order to incorporate areas near those with significant concentrations of cropland. This set of “farmland landscape” squares was analyzed to determine its composition, using the land cover data for the underlying 30-meter pixels. These data are aggregated using standard regions adopted by the Natural Resources Conservation Service (http://www.nrcs.usda.gov/technical/land/meta/m2140.html). The following land cover types were reported, based on NLCD categories: farmland, forest, grasslands/shrublands, “developed,” wetlands, water, other (see the national extent technical note for further details).

Data Quality/Caveats: Note that, in some cases, wetlands are found on croplands, and it can therefore be difficult to separate one from the other. This is especially true because these wetlands may only have water for parts of the year and may be farmed for other parts of the year. Thus, the data on wetlands reported in this indicator should be interpreted with some caution.