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published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution.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.

Ecosystem Types

This report uses six major ecosystem types as its basic reporting units.

• Coasts and Oceans
• Farmlands
• Forests
• Fresh Waters
• Grasslands and Shrublands
• Urban and Suburban Areas

This scheme is intended to cover all the lands and waters of the United States, including the ocean out to the limit of U.S. national jurisdiction. Obviously, these broad ecosystem or land cover types are neither homogeneous nor mutually exclusive. For example, the grasslands and shrublands ecosystem includes bare-rock desert and tundra, as well as the prairies and shrubland its name evokes. Freshwater wetlands are described along with lakes, streams, and so on, but are also tallied within the acreage of forests, farmlands, and other land covers. We describe each ecosystem type, including overlaps with other types, in greater detail in the opening section of each ecosystem chapter.

Map 4.2 shows where these ecosystems occur.

Coasts and Oceans. This ecosystem consists primarily of estuaries and ocean waters under U.S. jurisdiction. Estuaries are partially enclosed bodies of water (this term includes bays, sounds, lagoons, and fjords); they are generally considered to begin at the upper end of tidal or saltwater influence and end where they meet the ocean. By definition, U.S. waters extend to the boundaries of the U.S. Exclusive Economic Zone (EEZ), which extends 200 miles from the U.S. coast, but not all indicators report on this entire area. In addition, several indicators characterize shorelines along both estuaries and oceanfront areas. In these cases, we focus on the margin between land and water, not on uplands or watersheds that may influence coastal conditions.

Farmlands. We focus both on croplands—lands used for production of annual and perennial crops and livestock—and on a larger farmland landscape, which includes field borders and windbreaks, small woodlots, grassland or shrubland areas, wetlands, farmsteads, small villages and other built-up areas, and similar areas within and adjacent to croplands. Some indicators focus on croplands only, while some describe the entire farmland landscape.

Forests. We generally rely on the USDA Forest Service definition of forest: lands at least 10% covered by trees of any size, at least one acre in extent. This includes areas in which trees are intermingled with other cover, such as chaparral and pinyon–juniper areas in the Southwest, and both naturally regenerating forests and areas planted for future harvest (plantations or “tree farms”).

Fresh Waters. Our freshwater ecosystems include

• Rivers and streams, including those that flow only part of the year
• Lakes, ponds, and reservoirs, from small farm ponds to the Great Lakes
• Groundwater, which is often directly connected to rivers, streams, lakes, and wetlands
• Freshwater wetlands, including forested, shrub, and emergent wetlands (marshes), and open water ponds
• Riparian areas—the usually vegetated margins of streams and rivers (although this term can also apply to lake margins)

Obviously, there are overlaps and gradations among these systems. Wetlands often occur at the margins of streams and rivers, in what is also considered the riparian area. Some ponds are shallow and thus may also be classified as wetlands. In some rivers, dams create reservoirs, and these may be classified as rivers, reservoirs, or both.

Grasslands and Shrublands. The title of this system (which many people call rangelands) is quite descriptive: lands in which the dominant vegetation is grasses and other nonwoody vegetation, or where shrubs (with or without scattered trees) are the norm. Bare-rock deserts, alpine meadows, and arctic tundra are included in this system as well. We also include pastures and haylands, which represent an overlap with the farmland system; less-managed pastures and haylands fit well within the grassland/shrubland system, while more heavily managed ones fit well as part of the farmlands system. Most monitoring programs do not distinguish between the levels of management for pastures, however.

Urban and Suburban Areas. This system consists of those places where the land is primarily devoted to buildings, houses, roads, concrete, grassy lawns, and other elements of human use and construction. Urban and suburban areas, in which about three-fourths of all Americans live, span a range of density, from the unmistakable city center, characterized by high-rise buildings, concrete, and relatively little green space, to the suburban fringe—where development thins to an obviously rural landscape. This definition does not include all developed lands. It includes areas that we believe are large enough and built-up enough to qualify as “urban and suburban.” Many areas—small residential zones, the area of rural interstate highways, farmsteads, and the like—are “developed” but would not be considered “urban or suburban.”