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LEVEL III AND IV ECOREGIONS OF NEVADA
Description:
Ecoregions denote areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources. They are designed to serve as a spatial framework for environmental resource management. Ecoregions are directly applicable to the immediate needs of state agencies, including the selection of regional stream reference sites, the development of biological criteria and water quality standards, and the establishment of management goals for nonpoint-source pollution. They are also relevant to integrated ecosystem management, an ultimate goal of many federal and state resource management agencies. This map depicts revisions and subdivisions of ecoregions, compiled originally at a relatively small scale (USEPA 2000, Omernik 1987). Compilation of this map, performed at the larger 1:250,000-scale, is part of several collaborative projects primarily between the U. S. Environmental Protection Agency (EPA) National Health and Environmental Effects Research Laboratory (NHEERL), the U.S. Department of Agriculture's Natural Resources Conservation Service (NRCS), and state environmental resource agencies. Collaboration and consultation also occurred with other state and federal agencies, including the U.S. Forest Service and U.S. Geological Survey, in an effort to obtain consensus regarding alignments of ecological regions. The approach used to compile this map is based on the premise that ecological regions can be identified through the analysis of the patterns and the composition of biotic and abiotic phenomena that affect or reflect differences in ecosystem quality and integrity. These phenomena include geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology. The relative importance of each characteristic varies from one ecological region to another regardless of the hierarchical level. A Roman numeral hierarchical scheme has been adopted for different levels of ecological regions. Level I and Level II divide the North American continent into 15 and 52 regions, respectively (Commission for Environmental Cooperation 1997). At Level III, the continental United States contains 104 regions and the conterminous U.S. has 84 ecoregions (U.S. EPA 2000). Level IV is a further subdivision of the Level III ecoregions. Explanation of the methods used to define the ecoregions are given in Griffith et al. (1994, 1997, 2001), Omernik (1995, 2000), and Gallant et al. (1989). Regional collaborative projects such as these state efforts, where the goal is to reach consensus among resource management agencies, comprise a step in the direction of reaching the objectives of the Memorandum of Understanding for developing a common framework of ecological regions (McMahon et al. 2001). A common spatial framework would allow integrated ecosystem-type resource management across agencies having different responsibilities and interests for the same geographic areas. Reaching that objective requires recognition of the differences in the conceptual approaches and mapping methodologies that have been used to develop the most commonly used existing ecoregion-type frameworks, including those developed by the U.S. Forest Service (Bailey and others 1994), the U.S. EPA (Omernik 1987, 1995), and the NRCS (U.S. Department of Agriculture - Soil Conservation Service 1981). As each of these frameworks is further developed, the differences between them are becoming less. Collaborative projects at the state and regional level, where agreement can be reached among multiple resource management agencies, is a step in the direction of attaining commonality and consistency in ecoregion frameworks for the entire nation. The purpose of producing this map of Level III and IV Ecoregions of EPA Nevada is to: 1) highlight the current status and progress of ecoregion projects; 2) illustrate the hierarchical nature of the ecoregions; and 3) promote discussion and debate about the location of boundaries, level of consistency from state to state, and areas in need of revision. Comments and suggestions should be addressed to Sandy Bryce, Dynamac Corp., 200 SW 35th Street, Corvallis, OR 97333, (541) 754-4788, email: sandra.bryce@epa.gov., or to James Omernik, U.S. EPA - NHEERL, 200 SW 35th Street, Corvallis, OR 97333, (541) 754- 4458, email: omernik.james@epa.gov.