National Indicators:
Acres of Major Terrestrial Ecosystems

Ecological systems, conventionally referred to as ecosystems, are interconnected communities of living organisms, including humans, and the physical environment (e.g., climate, fire, hydrology, geology, topography) in which they interact. Stressed ecosystems are those ecological systems that are diminished or degraded through habitat loss, fragmentation, or contamination and that no longer support complete, thriving populations of native flora and fauna. These ecosystems are unable to sustain the full range of ecological functions (e.g., supporting normal animal migration patterns).

Ecosystems and their component species provide us with food, fuel, fiber, medicines, and natural capacities for cleansing the air and water. The full function of most species is not completely understood, but each has an important role to play in the “web of life.” As we gain a better understanding of the structure and function of ecosystems, we are better able to identify and implement the steps needed to restore ecosystems that are in decline.

There have been significant changes in the size and ecological integrity of some ecosystems since the middle of the 18^th century. Approximately 21 ecosystems in the United States have been identified as being particularly stressed:

• South Florida landscape
• Southern Appalachian spruce-fir forest
• longleaf pine forests and savannas
• eastern grasslands, savannas, and barrens
• northwestern grasslands and savannas
• California native grasslands
• coastal communities in the lower 48 states and Hawaii
• southwestern riparian forests
• Southern California coastal sage scrub
• Hawaiian dry forest
• large streams and rivers in the lower 48 States and Hawaii
• cave and karst systems
• tallgrass prairie
• California riparian forests and wetlands
• Florida scrub
• ancient eastern deciduous forest
• ancient forest of Pacific Northwest
• ancient red and white pine forest of the Great Lakes States
• ancient Ponderosa pine forest
• midwestern wetlands
• southern forested wetlands

It should be emphasized that the graph shown above does not include agricultural ecosystems, and most of the declines we have seen in other terrestrial ecosystems have been due to agricultural conversion. Although this indicator reflects the success of efforts to restore forests, rangelands, and wetlands in recent years, it does not reflect the important trade-offs between maintaining those ecosystems and meeting agricultural and urban land needs.

References:

• Dahl, T. E and G. J. Allord, History of Wetlands in the Conterminous United States, in USGS National Water Summary on Wetland Resources, Water Supply Paper 2425, 1996.
  
• Council on Environmental Quality, Environmental Trends, 1989.
  
• Council on Environmental Quality, Environmental Quality: 25^th Annual Report, 1994-95.
  
• Noss, R. F. and R. L. Peters, Endangered Ecosystems: A Status Report on America;s Vanishing Habitat and Wildlife, The Defenders of Wildlife, 1995.
  
• Noss, R. F., E. T. LaRoe III, and J. M. Scott, Draft Report: Endangered Ecosystems of the United States: A Preliminary Assessment of Loss and Degradation, U.S. Department of the Interior, 1995.