Methods

The Land Cover Trends project uses the EPA defined Level III ecoregions as the spatial framework for national assessment and reporting. Ecoregions are designed to serve as a spatial framework for environmental resource management. They denote areas that contain a geographically distinct assemblage of environmental conditions, natural communities, and plant species. The rates of land use and land cover change are estimated using a stratified random sampling of 10-km by 10-km blocks allocated within the ecoregion framework.

For each sample block we use historical Landsat Multispectral Scanner (MSS), Thematic Mapper (TM), and Enhanced Thematic Mapper Plus (ETM+) satellite images to interpret land cover change for each sample block on five separate dates (nominally 1973, 1980, 1986, 1992, and 2000). Historical aerial photographs from roughly equivalent times are used as ancillary information sources. We then use the sample block land cover data to analyze the spatial, temporal, and sectoral dimensions of change. We identify and document the forces driving land cover change using field observation, socio-economic data analysis, and a synthesis of published literature. You can find a full discussion of the project methodology in Loveland et al. (2002).