12 Wetland Assessment Criteria 



Ecoregions (Bailey, 1978) are a hierarchical classification of areas 

 characterized by distinctive flora, fauna, land forms, climate, vegetation 

 and ecological climax. Ecoregion classification includes biotic and 

 abiotic factors. For the purpose of this NWPCP, ecoregions will be 

 determined from Figure 1, taken from Cowardin et al. (1979), page 27. 

 Use of ecoregions allows compilation, comparison and interpretation of 

 data based on biogeographical units rather than on political units (e.g., 

 States). 



The EPA's Corvallis Laboratory has modified the Bailey ecoregion 

 classification system for their use in priority planning regarding 

 regulatory protection of aquatic and wetland resources (Omernik, 1987). 

 This new system factors in land use in addition to climate, soils, geology, 

 vegetation and physiography for identifying distinctive ecosystems. 

 Although this system may have advantages for wetland trends studies, it 

 was not available when the trends study was conducted. 



An Index of Loss formula was developed by Frayer for use in comparing 

 the magnitude of loss for a wetland type during the 1954-74 study period 

 between ecoregion divisions or other units of interest (e.g., States). The 

 Index of Loss is expressed by the following equation: 



(Y-XxlQQ) X (Y-XxlOQ) : or (Unit Loss x 100) x (Unit Loss x 100) 

 N Y Net National Loss 1954 Unit Base 



Where, Y = 1954 Unit Base acreage per wetland type and unit area; 



X = 1974 Remaining acreage per wetland type and unit area; 



Y-X = Unit Loss (e.g., 1954-74 State loss per wetland type); and 



N = 1954-74 Net National Loss per wetland type. 



Unit = Area of comparison (e.g., ecoregion, State) 



Base = Acres of wetlands in 1954 for the unit. 



Example: The subtropical ecoregion had 1,000,000 acres of palustrine 

 forested wetlands in 1954 and only 500,000 acres in 1974. The 1954-74 net 

 national loss of this wetland type was 6,000,000. 



Index of Loss = 417 (high) 



An Index of Loss number (as translated to a high, moderate or low value) 

 was developed by the Service for each non-coastal wetland type 

 experiencing a loss during the 1954-1974 study period: palustrine 



