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Wetlands of the United States

Their Extent and Their Value To Waterfowl and Other Wildlife

The Wetlands Inventory

The need for conducting a national wetlands inventory began to be apparent several years ago. It was common knowledge that drainage and other reclamation activities were steadily depleting the once-abundant wetlands available to wildlife, but there was no reliable and comprehensive information at hand to show the distribution, extent, and quality of the remaining wetlands in relation to their value as wildlife habitat.

More basic information on the relation of wetlands to wildlife was obviously a necessity, so the idea of conducting an inventory was kindled. In order that results might be most useful, it was agreed to place primary emphasis on wetlands considered susceptible to drainage or other land-use changes that destroy wildlife habitat. It is reemphasized here that permanent lakes, streams, and reservoirs were not included as wetlands.

County map

The broad aim was to make the coverage as complete as time and manpower would permit. Aerial photographs, topographic maps of the U. S. Geological Survey, charts of the U. S. Coast and Geodetic Survey, type maps of the U. S. Forest Service, soil maps and land-use maps of Federal and State agencies, and county highway maps proved to be helpful sources of information on the locations of wetlands. With these, and with the help of State fish and game departments and other agencies, field work for the inventory was completed in June 1954. It included an estimated 90 percent or more of all wetlands used significantly by waterfowl. Information on use by other wildlife was also collected.

This national report contains some of the gross results, such as acreages by values for the 48 States (table 6), and the general distribution and relative importance to waterfowl of the 74.4 million acres of wetlands included in the inventory (pl. 21). More detailed information for specific States and counties is on file for reference purposes in the Fish and Wildlife Service's regional offices, where inventory reports for individual States have been made available in limited quantity.


The shading on plate 21 indicates the general areas where wetlands included in this report are located. Fieldmen responsible for the inventory of a State had first to decide which regions of the State to cover in order to be certain of including at least 90 percent of the State's important waterfowl wetlands. In the North Central States (including the two Dakotas and the Lake States), virtually complete coverage of all wetlands, regardless of size, was considered essential in order not to neglect the all-important duck-breeding wetlands, which are widely scattered in these regions. The Southeastern States were given similar coverage, regardless of the importance of their wetlands to waterfowl.

Elsewhere in the country (Northeast and West), coverage was restricted to physiographic regions where good waterfowl habitat is most abundant. These were usually associated with inner basins, plateaus, high plains, and major rivers in the West, and with coastal regions and inland river drainages in the Northeast. In regions delineated for inclusion in the inventory, most wetlands less than 40 acres in size were excluded because they were too difficult to survey within reasonable time limits.

The portions of States not included in the inventory consist largely of small, scattered units of relatively low waterfowl value. Many of these units are in no danger of being disturbed by agricultural or industrial developments, and their inclusion in this inventory would have been prohibitively costly. An example of this prohibitive cost would be an attempt to appraise a high mountainous region containing unmapped meadows, beaver flowages, and wooded swamps.

Wetlands were recorded on county maps either as specific units or as general areas. In the Northeast and West, where only parts of States were studied and where only the larger areas were mapped, most wetlands were treated as specifically located units. This was true also of most States in the southeastern part of the country. But in the North Central States, the Lake States, and a few Southeastern States, where thousands of small scattered wetlands were encountered, fieldmen were compelled to collect acreage data and other information by sampling methods in order to complete their assignments.

Field sampling does not permit the recording of data on every specific area, but it does provide the basis for estimating the quantity and quality of a given wetland type in a given unit area--in this case, a county. In each county where this general coverage was followed, estimates of the amount, type, and quality of the wetlands were obtained. Also, certain of the larger and more important wetlands within the sampled units were covered and mapped as specific units.


It is important, both to wildlife biologists engaged in habitat preservation and to agricultural technicians making land-use recommendations for private lands, to understand the different ecological types of wetlands. Before the inventory was started, therefore, the Fish and Wildlife Service, through a committee of wetland ecologists, established and described 20 basic wetland types [9]. These types range from basins or flats that undergo only seasonal submergence (well-drained much of the summer) to lands that are waterlogged or flooded during most or all of the growing season.

Table 5 introduces the subject of classification by listing the 20 wetland types found in the country, with a brief description of the water depth and a total-acreage figure for each type. National totals show that 63.5 million acres are in the INLAND FRESH category. Totals by other categories (in millions of acres) are as follows: INLAND SALINE, 1.6; COASTAL FRESH, 4.0; COASTAL SALINE, 5.3.


Value categories of high, moderate, low, and negligible were set up to show the relative importance of wetlands to waterfowl in each State. Opinions of State biologists, State game wardens, and Federal game-management agents were relied on heavily in reaching value determinations. These categories can be used as general guides by wildlife agencies and public land-use agencies to determine the relative worth of wetlands to waterfowl in each State.

Wetlands in the breeding-range States were appraised with special consideration of their suitability for production purposes. Wetlands in the southern tier of States were judged primarily on their relative values as wintering habitat. Migration and hunting use received first consideration in other States. Therefore, at the present time there is no common denominator for interstate comparisons of wetland values assessed during the course of the inventory, but in general the wetlands with the highest ratings in each State are the ones receiving the greatest duck use.

It is stressed that waterfowl values represent the relative importance of wetlands to ducks and geese as determined by individual State standards rather than by National standards. The high value category means that areas so indicated for a particular State constitute the best habitat in that State. Values then scale down to negligible according to the degree of attraction to waterfowl.

If National standards had been used, they would have been based primarily on the number of waterfowl using a unit of area during particular seasons of the year. Under such a system, States with comparatively few ducks and with relatively poor habitat would have their best habitat rated low or negligible. This would be unfair to the wildlife interests of those States because they naturally want to preserve the best habitat they have, regardless of how it compares with other sections of the country. Neverthless, a system based on National standards would have great usefulness for planning nationwide waterfowl programs, and probably such a system should eventually be developed.

The following statements on the meaning of values can be used as guides when drainage or other land-use changes are contemplated:

High. -- Habitat of highest waterfowl use in present condition, the largest areas of which should be included in either Federal or State waterfowl-management programs, if feasible. If areas are small, numerous, and privately owned, wildlife use should receive top consideration by land-use agencies, and every encouragement should be offered to keep the land in a use-category that is favorable to waterfowl and other wildlife.

Moderate. -- Habitat of significant waterfowl use in present condition. Many areas should be controlled or managed by Federal, State, or private waterfowl organizations. Wildlife use of areas should receive consideration in land-use planning at least equal to alternative uses.

Low. -- Habitat receiving relatively low waterfowl use under natural conditions, but may be important locally as a shooting area for waterfowl or other game. Although loss of some of these areas might not be particularly harmful to waterfowl, public agencies should look upon them as possessing opportunities for habitat improvements which would help offset losses elsewhere. On the breeding grounds of the Plains States, innumerable areas are individually of low value but collectively they make definite contributions to the region's value for waterfowl.

Negligible. -- Habitat receiving little or no waterfowl use, although values for other wildlife may be substantial. Extensive development, probably at considerable expense would be required to increase waterfowl values in most areas, but opportunities for feasible development exist in others. Possibilities of such improvements should be explored. Drainage, or other land-use changes, would be least objectionable from a strictly waterfowl standpoint.

Those who use the present inventory are cautioned not to regard those wetlands classified in the two lower-value categories as automatically expendable, because such lands may have development potentials for wildlife. Another important point to consider is the value of distributing waterfowl widely by improving the quality of the poorer habitat in regions now supporting small populations of waterfowl.

Expansion of good-quality habitat will not only broaden the habitat base that now limits waterfowl populations and hunting opportunities, but it also will help prevent the build-up of concentration areas where crop depredations and disease outbreaks are more likely to occur. The inventory data, if used jointly in planning water-control facilities and waterfowl-management programs, can serve as an effective starting point for wetlands improvement as well as for wetlands preservation.

The values of wetlands to waterfowl as determined from the present inventory are shown, by States, in table 6. National totals show approximately 9 million acres of wetlands rated high, 13.5 million acres rated moderate, 24 million acres rated low, and 28 million acres rated negligible. Plate 21 depicts the nationwide distribution of wetlands by waterfowl values. Not included in table 6 or in plate 21 are 3,812,000 acres of overflow and seasonally flooded lands presently used for crops or pasture. Although these agricultural wetlands are identified on state wetlands maps by a special symbol and listed in State reports (as non-add items), they are not combined with other wet and waterlogged lands because the present inventory encompasses only natural wetlands that have been little altered by man's activites.

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