[PCA] WEB: Report on Biodiversity of Isolated Wetlands by NatureServe

[Olivia Kwong]

NatureServe
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Biodiversity Values of Geographically Isolated Wetlands in the United 
States

As a result of a 2001 Supreme Court decision (Solid Waste Agency of 
Northern Cook County vs. U.S. Army Corps of Engineers, 2001), some 
wetlands and other waters that are considered "geographically isolated" 
from navigable waters no longer fall under the jurisdiction of the Clean 
Water Act.  Scientific assessments of the potential impacts of the court's 
decision are needed to provide guidance to the federal agencies, states, 
tribes and local governments that will have responsibility for protecting 
these valuable resources.

In this study we sought to assess potential impacts of the court's 
decision on the nation's biological diversity. To do so, we first used a 
nationally standardized classification of wetland ecological systems.  We 
then established a working definition to categorize types as 
"geographically isolated," and using expert knowledge of these wetland 
types, we narrowed the national list of wetland ecological systems to 
those that tend to occur "geographically isolated" from navigable waters. 
Through review of scientific literature, input from regional experts, and 
compilation of existing location data for at-risk species, we identified 
those at-risk species and plant communities (those species and communities 
considered rare, imperiled or critically imperiled using NatureServe's 
standard criteria) that are supported by these isolated wetland types 
throughout the United States.

This assessment used the best currently available information. Because 
comprehensive wetland maps are unavailable nationally, this study focuses 
on documenting the number, or diversity, of isolated wetland types, rather 
than on the acreage these wetland types occupy. These analyses could be 
significantly augmented in the future with the collection of additional 
data on the occurrence of isolated wetland types, their spatial extent, 
and their associated species and communities.

Key Findings

Significant wetland diversity exists in every state of the nation. Of 276 
types of wetland described for the United States, 81 (29%) met our 
project-specific definition of "geographically isolated." These types of 
wetlands may no longer be regulated under the Clean Water Act.  Their 
regulation will therefore largely be determined by how lawmakers, 
regulators, and the courts interpret the term "isolated."  Of the 636 U.S. 
terrestrial ecological system types (both upland and wetland) currently 
classified and described by NatureServe (NatureServe 2005), these 81 
isolated wetland types amount to 13% of all "natural/near-natural" 
terrestrial ecological system types.

This study documents that isolated wetland ecological systems support high 
levels of biodiversity, including significant numbers of at-risk species 
and plant communities. For example:

  - A total of 274 at-risk plant and animal species are supported by 
isolated wetlands, with more than one-third (35%) apparently restricted to 
these wetland types. At-risk animal species are even more closely tied to 
isolated wetlands; more than one-half of at-risk animals considered in 
this study appear to be obligate to isolated wetland habitats.
  - A total of 86 plant and animal species listed as threatened, 
endangered, or candidates under the Endangered Species Act are supported 
by isolated wetland habitats.  This represents about 5% of all plant and 
animal species currently listed under the Act.  A majority (52%) of these 
listed species are completely dependent on isolated wetland habitat for 
their survival.
  - Nearly half of isolated wetland types (35 of 81, or 43%) are known to 
support at least one listed species under the Endangered Species Act.
  - On average 6% of the at-risk plant species in a given state are 
directly supported by isolated wetlands.
  - Nearly one-quarter of U.S. counties (725 counties, or 23%) harbor at 
least one at-risk species associated with isolated wetland habitats, and 
80 of these counties have five or more such species.  Ten or more at-risk 
species associated with isolated wetlands are confirmed from 18 counties 
of California, South Carolina, North Carolina, Georgia, Alabama, Nevada, 
and Hawai'i.  Merced County, California leads with 20 at-risk species tied 
to isolated wetland habitats.
  - A total of 279 at-risk vegetation associations (9% of all plant 
community types classified in the U.S. National Vegetation Classification) 
were documented as being characteristic of isolated wetlands, and 
two-thirds (67%) of these associations are not found in any other types of 
habitat.

Wetlands that can be considered "geographically isolated" represent a 
considerable amount of the United States' ecological diversity and provide 
habitat for a considerable portion of the nation's flora and fauna. 
Significant loss of isolated wetland habitats could seriously affect 
opportunities for the survival and recovery of the many rare or endangered 
species that depend on them.

States, tribes and local governments will increasingly be in a position to 
decide the fate of those isolated wetlands that no longer are protected 
under the Clean Water Act.  The information and analyses contained in this 
study are designed to assist policy-makers and land managers at federal, 
state, and local levels to better understand their biodiversity value and 
plan for their conservation.

At Risk Elements (ranked G1-G3 by NatureServe) Tied to Isolated Wetlands
 	Obligate  Facultative  Unknown  Total
Animals  18        12           3        33

Plants   77        141          23       241

Total    95        153          26       274
Species

Associations
          176       103          0        279


Federally Listed Species Tied to Isolated Wetlands (a subset of "At Risk 
Species)

 	Obligate  Facultative  Total

Animals
          8         5            13
Plants   37        36           73
Total    45        41           86


Contributing Authors
Patrick Comer, Kathy Goodin, Adele Tomaino, Geoff Hammerson, Shannon 
Menard, Milo Pyne, Marion Reid, Marcos Robles, Mary Russo, Lesley Sneddon, 
and Kristin Snow

Acknowledgements
We wish to express our sincere appreciation to biologists and ecologists 
from the natural heritage programs that contributed expertise, review and 
data. The extensive field experience represented by this network of 
scientists and their close working partners form the basis for this 
analysis. We are grateful for the financial assistance provided by the 
U.S. Environmental Protection Agency (EPA), Office of Wetlands, Oceans and 
Watershed - Wetlands Division through a Wetlands Program Development 
Grant.

The complete report is available for download on NatureServe's website: 
www.natureserve.org