identical. 2^ An example of similar stands in similar habitats is the 

 intimate relationship that exists between vegetation and topog- 

 raphy in Island Beach State Park, New Jersey. This relationship 

 is especially constant in herbaceous stands which occupy facets 

 characterized by limiting environmental conditions, such as 

 dunegrass communities on primary foredunes, the true salt marsh 

 occurring in intertidal peat flats, and nearly all the reedgrass 

 communities on low sandy ridges parallel to the shoreline. ^'^'^ 

 Neither does the concept of community type, or abstract com- 

 munity, require that all habitats resembling one another should 

 be occupied by similar groupings, for such habitats may be so 

 widely separated — grasslands in the Ukraine and in North 

 America for example — that the constituent species of each have 

 been prevented by natural barriers from migrating from one to 

 the other. Vegetation in similar habitats may also differ because 

 the stands are in various stages of succession or the sources of the 

 disseminules may be located at various distances. 



While the stands in a community type are not precisely alike, 

 the inclusion of similar groupings under one category is most 

 useful in the interpretation of relations between vegetation and 

 environment, and is as logical as many other kinds of classifica- 

 tion. The resemblance between stands is neither superficial nor 

 accidental, as stated by Gleason,^° but is often profound, as shown 

 by the high degree of relationship between vegetation and 

 environment as compared to other kinds of stands in the same 

 geographic area. It seems impossible that each community is the 

 product of its own independent causative factors,^° for many 

 interrelations between species in different stands do exist such as 

 pollination, seed dispersal, feeding of animals, and the spreading 

 of parasites. Because of these interrelationships a plant commun- 

 ity cannot be a wholly individualistic entity — barriers completely 

 isolating communities or ecosystems simply do not exist here.^° 



Since habitats differ; since species differ in their requirements, 

 ecological amplitudes, and relations with other species; and be- 

 cause some habitats and stands are similar, it is to be expected 

 that groupings of different degrees of resemblance can be made. 

 Similarity in habitat is often indicated by the physiognomy, life- 



CSrovmpixmg of Species • 67 



