The ecological communities used in this classification are interrelated assemblages of flora, fauna, and other biotic and abiotic features. A particular ecological community tends to occur repeatedly under a similar set of environmental conditions (i.e., soils, geologic substrate, hydrology, climate, microclimate, topography, and aspect). These communities are delineated based on the potential natural vegetation and the dominant or characteristic plant species that naturally occur (or occurred) in a given region of the country. In today’s landscape, very little undisturbed natural vegetation remains. Almost all areas of the country have either been converted to other uses (i.e., cropland, pasture, urbanization, and roads) or have been severely modified through logging, grazing, mining, or flooding.
The term “potential natural vegetation” is used to indicate the vegetation which did or would naturally occur without the influence of modern civilization. Natural vegetation is considered from the time frame of the natural conditions which greeted the first Euro-American settlers. Because most of the landscape has been modified, determining the potential natural vegetation for a specific site may be difficult; however, it should be one of the first steps in choosing the appropriate ecological communities for your site. Ecological communities considered rare, or of very limited extent within a region, are not included in the community descriptions although they may be mentioned in the regional description. For example, glades are mentioned in the New England Region but a description and species list are not given because they are extremely rare and are of very limited extent. However, in the Ozark/Interior Plateaus Region, glades are described as a dominant ecological community because they are more common and occupy considerable acreage.
The ecological community descriptions and accompanying lists of species were also compiled from many sources. State and regional floras, state Natural Heritage Program data, and many other books and articles were used. Because of this variety of sources, all plant names, both common and scientific, have been standardized with Kartesz (1990 and 1991). Although locally important, subspecies and varieties have not been used because of the large areas covered by the dominant ecological communities in each natural region. Communities can be identified and described at many levels from the largest, the earth, to the smallest, a drop of pond water. This classification falls somewhere in between. We attempted to define the ecological communities at a useful level for national reference without losing too much of the detail of smaller community divisions. It must be realized that individual species, although a component of a community in a particular area, may not occur over the entire geographical range of the community. For that level of detail, one should consult local experts in the state Natural Heritage Programs, native plant societies, environmental groups, or universities.