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museums. It is altogether likely that some of this information is 

 outdated, given the rapid rate of habitat modification taking place 

 in the region, and ideally all this information should be rechecked, 

 especially in the case of data about wetlands, coastal areas and 

 islands. 



At the same time, from the standpoint of making an ecological 

 survey, there are great gaps in our knowledge. It is not always 

 known, for example, what the correlation is between plant communi- 

 ties of various sorts and the niches of some animals, especially 

 migratory ones. Nor is it always known what the tolerances of 

 various plants and animals are to various changes in environmental 

 quality. Faced with such gaps, the Center for Natural Areas was 

 forced to rely on several traditional sets of parameters in classi- 

 fying and ranking the natural areas of this vast region. 



Important Biotic Communities 

 No natural ecosystem, even a simplified version such as a plant 

 community, is discreet. All are bounded by gradients (ecotones) 

 where the species characteristic of one habitat are gradually 

 replaced by those of another. At its upper edge a salt marsh 

 merges into a freshwater marsh which in turn passes without break 

 into the forest on its edge. Only men make maps with lines on 

 them, but such map lines— and categories — are necessary. The 

 Chesapeake Bay region is rich in the categories of biotic 



