Our Liviiii; Rcsoiiives — Habitiit Assessments 



475 



forested wetlands sut'fered tremendous loss 

 from agriculture and ■"other" uses. (The catego- 

 ry of ""other" includes all wetland areas convert- 

 ed to upland where the ultimate land use could 

 not be determined.) Thousands of hectares of 

 forested wetlands were converted to emergent, 

 scrub-shrub, and nonvegetated wetlands. 

 Likewi.se, thousands of hectares of scrub-shrub 

 wetlands were converted to the ""other" catego- 

 ry and the agricultural land-use category. These 

 losses were nearly offset by the conversion of 

 forested wetlands to scrub-shrub wetlands. 

 Despite these gains to the scrub-shrub category, 

 however, there was an overall net loss of scrub- 

 shrub wetlands during the study period. 



The net gain of thousands of hectares of 

 freshwater emergent wetlands is similarly 

 deceptive. The thousands of hectares that were 

 lost to agricultural, ""other," and urban land uses 

 were more than offset by the conversion of 

 forested wetlands and scrub-shrub wetlands to 

 freshwater emergent wetlands. The area of non- 

 vegetated wetlands (primarily ponds) increased 

 by several million hectares. Most of these gains, 

 however, resulted from construction of ponds 

 on uplands not used for agricultural production, 

 but additional thousands of hectares were built 

 on former agricultural lands. This category also 

 experienced gains from converted forested wet- 

 lands and scrub-shrub wetlands. 



Functions and Values 



The functions and values of the nation's wet- 

 lands are nearly as diverse as the wetlands 

 themselves (Table), but include flood protection 

 and plant, fish, and wildlife habitat. 



All wetlands do not perform all functions. 

 Some functions tend to be compatible, such as 

 flood control and water purification. Other 

 functions tend to be incompatible, such as flood 

 control and food chain support. In addition, 

 wetlands of a given type do not have the same 

 effectiveness in performing a given function. 

 For example, the effectiveness of a given forest- 

 ed wetland for flood control depends on its size, 

 shape, location in the watershed, and so forth. 

 Because wetlands are constantly being affected 

 by disturbance, their effectiveness in perform- 

 ing functions constantly changes. Thus, the 

 effectiveness of a wetland area as wildlife habi- 

 tat can be improved or degraded by the creation, 

 maintenance, or destruction of vegetated corri- 

 dors; the ratio of vegetated wetland to upland 

 areas; buffer zones: and plants that provide for 

 wildlife food and habitat. Uplands can and do 

 perform some of the functions performed by 

 wetlands, such as sediment trapping. But 

 because wetlands are situated in the low points 

 of the land.scape or are adjacent to streams, 

 rivers, lakes, and oceans, they are more able to 



Table. Major wetland functions and values documented in the National Wetlands InventoiT.' 

 "Wetlands Values Databa.se." 



Functions and values 



Examples 



Biogeochemical processes Carbon cycling, sulfur cycling 



Food chain Detritus production, food source, nutrient cycling, nutrient export, primary production 



Habitat Amphibians, fish, furbearers, insects, mammals, nongame birds, reptiles, shellfish, shorebirds, 



waterfowl, endangered species 

 Hydrology Erosion control, flood control, flow stabilization, groundwater discharge, groundwater recharge, 



saltwater intrusion prevention, storm dampening 

 Socioeconomic Aesthetics, agricultural crops, aquacultute, archaeological, commercial han/esi, cultural, 



educational, energy source (peal), lood, lorage, heritage, hunting and trapping, indicator 



species, medicinal, open space, natural products, recreation, research, timber, wastewater 



treatmenl, water supply 

 Water quality Chemical and nutrient absorption, pollution filtering, oxygen production, sediment trapping 



perform these functions. In many cases, wet- 

 lands are the last line of defense for the protec- 

 tion of surface water quality. 



Some wetland functions and values can be 

 replaced by artificial substitutes; for example, 

 flood-control values of wetlands can be 

 replaced by dams, ditches, levees, floodwalls, 

 and reservoirs. Other wetland functions, howev- 

 er, cannot be performed by uplands or replaced 

 by artificial substitutes. An especially important 

 function of wetlands is supporting rich plant 

 diversity. Although wetlands occupy only about 

 5'7c of the surface area of the contemiinous 

 United States. 6.728 plant species (31% of the 

 U.S. flora) occur in wetlands (Reed 1988). Of 

 these plants, half are restricted to, or usually 

 occur in. wetlands. Thus, wetlands provide crit- 

 ical habitat for a high percentage of the U.S. 

 flora. 



Some argue that we cannot afford to main- 

 tain the remaining 40 million ha (99 million 

 acres) of wetlands in the conterminous United 

 States because of our increasing population, liv- 

 ing standards, and competition for resources. 

 Others argue that wetlands must occupy a 

 greater percentage of the nation's landscape. In 

 the conterminous United States, non-federal 

 rural land occupies nearly 75% of the landscape 

 and contains more than 75% of the nation's wet- 

 lands (USDA 1989). Wetlands comprise neariy 

 6% of the rural non-federal landscape. 

 Specifically, wetlands occupy roughly 1% of 

 cropland. 2% of rangeland, 5% of pastureland, 

 12% of forestland, and 31% of other rural land 

 (USDA 1989). 



Future 



Although our understanding of wetlands is 

 imperfect, it is clear we have more information 

 upon which to make public policy decisions on 

 wetlands than we have for many other ecosys- 

 tems. The challenge for policy makers is to 

 avoid ecologically irreversible choices that 

 would diminish the wealth of future generations 

 while promoting economic development and 

 improving income distribution. 



