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Habitat A.sst'ssmcnts — Our Lniiifi Resources 



Fig. 1. Surface-area percentage of 

 wetlands in each state: I780's 

 (Dahl 1990). 



Fig. 2. Surface-area percentage nf 

 wetlands in each state: 1980's 

 (Dahl 1990). 



□ 0.0 - 4 (Millions ot acres) 



□ 0.4-1,0 



□ 1.0-3.0 

 SI 3.0 -5.0 

 ■ 5.0 -10.0 



Fig. 3. Wetland acreage loss by 

 state (Dahl 1990). 



□ 0% - 20% 



□ 20% - 40% 



□ 40% - 60% 

 S 60% - 80% 

 ■ 80% -100% 



Fig. 4. Surface-area percentage of 

 wetland base loss by state (Dahl 

 1990). 



convei'sion has slowed, wetland losses continue 

 to outdistance gains (Fiayer et ai. 1983; Dahl 

 and Johnson 1991). 



The quality of the remaining wetlands con- 

 tinues to be an unanswered question. 

 Presidential candidate George Bush's 1988 No- 

 Net-Loss campaign promise was adopted hy the 

 federal government as a policy goal. It was 

 expanded by President Clinton in his August 25. 

 1993. policy statement. "Protecting America's 

 Wetlands: A Fair. Flexible, and Effective 

 Approach." to include a long-temi goal of 

 increasing the quality and quantity of the 

 nation's wetlands resource base. Here we pre- 

 sent a brief overview of wetlands, their defini- 

 tion, distribution and abundance, dynamics, 

 functions, values, and future. 



Wetland Descriptions and 

 Definitions 



The United States encompasses an area of 

 about 931 million ha (2.3 billion acres) extend- 

 ing from above the Arctic Circle to the Virgin 

 Islands and spanning the North American conti- 

 nent, and includes the Hawaiian Islands as well 

 as Puerto Rico. Within this broad area, regional 

 variations in climate, topography, hydrology, 

 geology, soils, and vegetation create diverse 

 wetland habitats ranging from the tundra in 

 Alaska to the tropical rain forests of Hawaii to 

 isolated wetlands in the arid Southwest. 



Cowardin et al. ( 1979) defined wetlands as 



lands where saturation with water is the domi- 

 nant factor determining the nature of soil devel- 

 opment and the types of plant and animal com- 

 munities living in the soil and on its surface. 

 The single feature that most wetlands share is 

 soil or substrate that is at least periodically sat- 

 urated with or covered by water The water cre- 

 ates severe physiological problems for all 

 plants and animals except those that are adapt- 

 ed for life in water or in saturated soil. (p. 3) 



There are three widely used definitions of 

 wetlands. All use three parameters: hydrology, 

 hydric soil (wetland soils), and hydrophytic 

 vegetation (wetland plants). The USFWS's def- 

 inition is ecological whereas the definitions 

 used by the U.S. Environmental Protection 

 Agency, the U.S. Anny Corps of Engineers, 

 and the Soil Conservation Service are regulato- 

 ry. All three, however, endorse and use the same 

 interagency wetland plant list. National List of 

 Plant Species Thai Occur in Wetlands (Reed 

 1988), and wetland soils list, H\dric Soils of the 

 United Slates (SCS 1991). 



Regulators are concerned with establishing a 

 definitive line to delineate wetlands from 

 uplands and with placing the wetlands into 

 administrative or regulatory categories. In con- 



trast, the USFWS and the National Biological 

 Service (NBS) are concerned with ecological 

 characterization and mapping the biological 

 extent of both vegetated and nonvegetated wet- 

 lands found on soils and substrates. The biolog- 

 ical extent of wetlands should be established by 

 scientists using biological criteria. Likewise, 

 policy makers should establish regulations for 

 the subset of wetlands that needs regulating. 

 The subset of wetlands to be regulated and the 

 degree of regulation have changed and will 

 change over time based on our understanding of 

 the functions and values of wetlands, wetlands 

 scarcity, our ever-changing social values, and 

 the political climate. 



The USFWS classification system was 

 developed to provide uniformity in concepts 

 and terminology for wetlands. It is hierarchical, 

 moving from systems at the broadest level 

 through subsystems, classes and subclasses, to 

 modifiers describing hydrology (water regime), 

 soils, and water chemistry, and special modi- 

 fiers relating to human activities. 



These categories are used to form wetland 

 types for mapping. More than 2,500 wetland 

 types are commonly used on National Wetlands 

 Inventory maps nationwide. Counties will have 

 from 10 to 400 types, with an average of 100. 

 These wetland types describe ecological units 

 that have certain homogeneous natural attribut- 

 es. The USFWS's National Wetlands Inventory 

 maps are available for 84% of the conterminous 

 United States. 28% of Alaska, and all of Hawaii. 



Distribution and Abundance 



The distribution of wetlands has changed 

 dramatically since the 1780's (Figs. 1 and 2). In 

 addition, the percentage of the landscape occu- 

 pied by wetlands varies markedly from state to 

 state (i.e.. Alaska, where 43.3% of the land- 

 scape is covered by wetlands as compared with 

 nine states where I % or less of the landscape is 

 covered by wetlands). The wetland areal loss by 

 states tells one story (Fig. 3) and the percentage 

 of the wetland base lost by states tells another 

 (Fig. 4). Wetlands occupy 11.9% of the land- 

 scape of the United States, which is about 5% of 

 the conterminous United States, 43% of Alaska, 

 and 1% of Hawaii. 



Wetland Dynamics 



The three status and trends reports to 

 Congress provide estimates of net wetland gains 

 or losses: they do not examine wetland quality 

 as a result of disturbance. Wetlands are con- 

 stantly being disturbed. Even when a wetland is 

 not converted to upland, its successional stage is 

 often pushed back to an earlier stage. For exam- 

 ple, between the mid-1970's and mid-1980's. 



