Natural Regions & Potential Natural Vegetation Regions

Natural Vegetation and Potential Natural Vegetation maps depict the distribution of vegetation communities across the landscape, and provide information about the physical characteristics and natural history of a region. Increased interest in the reclamation and restoration of disturbed areas, and in the interaction of humans and the landscape, has spurred research and mapping of the historic and modern vegetation. Vegetation maps thus provide valuable information about the environment on local and regional scales.  

Ecological systems
Ecological systems are categories which describe general ecological functions and processes. Upland (terrestrial), wetland (palustrine), and estuarine systems are included in this classification. The wetland definitions mainly follow the classification of Cowardin et al. (1979). True aquatic systems such as lakes, oceans, and rivers (called lacustrine, marine, and riverine systems, respectively) are not included. The upland, wetland, and estuarine systems are further subdivided into more specific classes. The classes are defined by the dominant life form of the vegetation which reflects the basic physiognomy or appearance of the habitat. Forest, woodland–barrens, shrub, and herbaceous are the classes used in this classification. The systems and classes are combined in the following definitions. These definitions are necessary because they help us distinguish between a wetland and an upland—or a forest and a woodland. The differences between systems or classes are often technical and difficult to recognize in the field. In order to analyze a site and determine the appropriate ecological community, it is necessary to be familiar with the systems and classes. The species lists for ecological communities are organized by regions and according to the following systems and classes.

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How were the Natural Regions and Potential Natural Regions Mapped?
We developed the classification system for the natural regions, ecological systems, and classes. This classification was developed to make it possible for someone anywhere in the country to determine what general types of ecological communities could occur at a particular site. Classification of the landscape and its natural vegetation has been approached from many different views and levels of detail, depending upon the purpose. It is fairly naive and simplistic to write down a series of categories and definitions and assume that nature has been neatly classified. It is uncommon in nature for regions or communities to be clearly delineated. Rather, they tend to grade into one another or form a mosaic, making it difficult to distinguish entities. However, classifying the landscape is the only way for us to study and comprehend an incredibly complex system. It is certainly necessary to provide a basis for what to restore and where. We have divided the United States into 30 Natural Regions. This natural regions classification system was developed using numerous sources. Because the level of detail in any single source was not thought to be adequate for our purposes, multiple sources of information were used to delineate the natural regions at the appropriate scale. The primary sources used to develop the natural regions were Potential Natural Vegetation of the Conterminous United States (Küchler 1964b, 1975), Ecoregions of the United States (Bailey 1978, 1994), Ecoregions of the Conterminous United States (Omernik 1986), and North American Terrestrial Vegetation (Barbour and Billings 1988). Using the Küchler (1964) and Bailey (1978, 1994) maps combined as a base, the country was divided into thirty natural regions. These natural regions generally follow Bailey’s regions and subregions as laid over Küchler’s potential natural vegetation map. Bailey has updated and changed the names of his regions and subregions from vegetation descriptions to other descriptors. The lines dividing regions generally follow a Küchler vegetation type. These natural regions are areas of the country that have certain natural features in common. These features include soils, geologic history, landforms, topography, vegetation types, plant and animal distributions, and climate. These natural regions are broad or coarse divisions which make it easier to subdivide and define the landscape and its vegetation.