However, guides to ecosystems are rare and often too technical and specialized for general use. One reason is that a guide covering a continent or part of one would span too many geographic areas and climates to cover the same species throughout. The complexity of such a guide would thereby be unmanageable. It is true that similar hydrologic systems and geologic origins may lead to different vegetation in the two zones. Nevertheless, the variation in wetlands within Wisconsin and Minnesota is small enough to be manageable, and this guide begins with a simple and workable outline-key for recognizing the main wetland types, which number only fifteen.
Vegetation is the handle by which wetland types can be most easily recognized.
Of course, vegetation is by no means the only element in wetlands. An example of human abuse is the introduction of alien pest species such as carp and purple loosestrife. Individual species have individual limits on their distribution that do not exactly coincide with those of any other, whereas a given wetland is sure to have several, if not all, of the characteristic species present. Since one type of wetland may grade into another, so that several types may occur in a single valley or basin, the locations of groups of species will help describe the actual situation, by mapping for the eye the gradients in environmental conditions that cause the wetland and its functions to vary from place to place. In other words, they know what information is pertinent and what questions to address.