Significant Topographic Changes in the United States
Ecoregions have been developed and are being used to study the place dependency of environmental processes, including anthropogenic transformations of the land surface. Ecoregions are also the basis for reporting on the status and trends of land cover and land cover change. As a geographic framework that is useful for studying the response of the environment to human activities, ecoregions form a useful basis on which to view the distribution of topographic changes across the United States.
This figure shows the Level III Omernik ecoregions from the Environmental Protection Agency that contain topographic change polygons.
Consideration of the top two ecoregions in terms of the number of change polygons, the Central Appalachians and the Northern Lakes and Forests, provides an interesting view into the differences between regions in the character of topographic changes.
The number of topographic change polygons and their total area for the Central Appalachians ecoregion is 1,195 polygons and 84.36 square kilometers. For the Northern Lakes and Forests ecoregion, the numbers are 427 polygons and 159.48 square kilometers. The Central Appalachians ecoregion has almost three times the number of change polygons as the Northern Lakes and Forests ecoregion, but those polygons cover only about half as much area.
Conversely, the Northern Lakes and Forests ecoregion only has about one-third the change polygons that the Central Appalachians ecoregion has, but those polygons cover twice as much area. Consequently, even though the topographic change polygons cover less area in the Central Appalachians ecoregion, their greater number and spatial arrangement likely result in more landscape fragmentation than in the Northern Lakes and Forests ecoregion. This relationship between the number of change polygons and their total area likely has important implications for habitat fragmentation, a key indicator of ecological condition. The sum of many smaller landscape changes can have a large cumulative effect, perhaps even more than the effect of a small number of very large change areas. Thus, when comparing the cumulative effects of topographic changes among different regions, it can be useful to consider the number of polygons to total area relationship. However, other regional conditions must also be considered to determine if that relationship is a reliable indicator of landscape impacts.
Summary Statistics and Rankings:
Top Ranked Ecoregions (by Area) Containing Topographic Change Polygons