Conservation Library


Delineation of Ecosystem Units

National Ecosystem Mapping

There have been numerous attempts to delineate ecosystems on a national scale, using a wide variety and combination of biological, physical and geoclimatic characteristics. Yet, no single mapping system or scale can capture all the information necessary to fully support an ecosystem approach to fish and wildlife conservation. Indeed, mapping strategies should be flexible and dynamic, much like the information they portray.

The Service has chosen the U.S. Geological Survey's Hydrologic Unit Map as the foundation for organizing and managing its diverse staff resources and program capabilities. This mapping strategy, based upon the delineation of watersheds, was chosen for several reasons including:

  • Watersheds are discrete physical units that provide widely recognized and generally well-defined boundaries.


  • Watersheds, by their hierarchical structure, lend themselves to a flexibility of scale necessary in a realistic and effective ecosystem approach.


  • Watersheds are of major ecological importance and provide an appropriate focus for aquatic, coastal, and estuarine habitats, in particular. Approximately 45% of the Nation's threatened and endangered species directly depend on aquatic and wetland habitats.


  • Watersheds provide a vehicle to consider the critical linkages between upstream and downstream effects.

The Service initially identified 52 "ecosystem units" by grouping or, in some cases, segmenting watershed units. Vegetation cover types, physiography, and optimum size were considered in the grouping of watersheds. The size of each ecosystem unit also reflects consideration of the amount of land area that can be effectively addressed and the commonalty of resource issues.

Over the past year, some ecosystem units were deleted from or added to the map, and the boundaries of other units were adjusted to reflect additional information and the views of Service partners. The Service remains flexible to consideration of future adjustments to the national map. Developing and mapping pertinent ecological information on a national scale to support conservation initiatives will continue in cooperation with other agencies.

Use of "Focus Areas"

The Service's watershed-based map provides a suitable framework around which to mobilize diverse staff resources. However, the most appropriate ecosystem boundaries can often be defined by the issues or problems to be resolved, resulting in delineation of areas on a scale much smaller than the Service's ecosystem units. Focus areas allow the Service to adapt to ongoing State, regional, or other management initiatives. In other cases, ecosystem planning boundaries may be determined by legislation. The ecosystem approach is intended to be flexible enough to allow the Service and its partners to customize the area of focus to fit the issue at hand.

Working Across Ecosystems

The Service's watershed map does not preclude the need to address important conservation objectives on larger spatial scales. Fish and wildlife population and habitat goals are based upon species biology, population dynamics, and ecological processes that may be international in scope (e.g., migratory waterfowl). Service managers must think and function at multiple scales simultaneously. Planning and implementation of management actions within the Service's ecosystem units must be flexible enough to address site-specific conservation priorities and reflect the broader population and habitat needs of widely ranging species.

                        "The practices we now call conservation are, to
                        a large extent, local alleviations of biotic pain. 
                        They are necessary, but they must not be confused 
                        with cures. The art of land doctoring is being 
                        practiced with vigor, but the science of land 
                        health is yet to be born."

                                    Aldo Leopold                

U.S. Fish and Wildlife Service Ecosystem Approach Watershed Based Units Map

Fish and Wildlife Service Ecosystem designations 126K

Fish and Wildlife Service Ecosystem designations Link to 126K half size, horizontal, color image

Fish and Wildlife Service Ecosystem designations 203K

Fish and Wildlife Service Ecosystem designations Link to 203K, page size, vertical, color image

U.S. Fish and Wildlife Service

Unit Name Lead   Region
1. North Pacific Coast  1
2. Klamath/Central Pacific Coast   1
3. Central Valley of California/ San Francisco Bay   1
4. South Pacific Coast  1
5. Columbia River Basin     1
6. Interior Basins   1
7. Lower Colorado River   2
8. Gila/Salt/Verde River 2
9. Middle and Upper Rio Grande 2
10. Lower Rio Grande 2
11. Pecos River 2
12. Edwards Plateau 2
 13. East Texas 2
14. Texas Gulf Coast 2
15. Arkansas/Red Rivers 2
16. Southern Appalachians 4
17. Upper Colorado River 6
18. Platte/Kansas Rivers 6
19. Upper Missouri/ Yellowstone Rivers 6
20. Missouri Main Stem 6
21. Lower Missouri River 3
22. Mississippi Headwaters/ Tallgrass Prairie 3
23. Upper Mississippi River/ Tallgrass Prairie 3
24. Great Lakes 3
25. Ozark Watersheds 3
26. Ohio River Valley 5
27. Lower Mississippi River 4
28. Tennessee/Cumberland River  4
29. Central Gulf Watersheds 4
30. Florida Panhandle Watersheds 4
31. Altamaha Watershed 4
32. Peninsular Florida 4
33. Savannah/Santee/Pee Dee Rivers 4
34. Roanoke/Tar/Neuse/ Cape Fear Rivers 4
35. Caribbean 4
36. Delaware River/Delmarva Coastal Area 5
37. Hudson River/New York Bight 5
38. Connecticut River/Long Island Sound 5
39. Gulf of Maine Rivers 5
40. Lake Champlain  5
41. Chesapeake Bay/Susquehanna River 5
42. Pacific Islands 1
43. Arctic Alaska 7
44. Northwest Alaska 7
45. Interior Alaska 7
46. Southeast Alaska 7
47. South Central Alaska 7
48. Bristol Bay/Kodiak 7
49. Yukon - Kuskokwim Delta 7
50. Bering Sea/Aleutian Islands 7
51. Beaufort/Chukchi Seas 7
52. North Pacific/Gulf of Alaska 7
53. South Florida 4


Continue on to the Service Ecosystem Teams

Last updated: April 1, 2010