Co7nmunity Type 447 



COMMUNITY CLASSIFICATION 



Since the community is essentially a functional unit, the size of the 

 area occupied by the community, the number of living things included 

 in it, and its organization are variable according to circumstances. As 

 we have seen, the groups of plants and animals that constitute a com- 

 munity may be large or small, and frequently one functional group is 

 contained within another. Furthermore, one community replaces 

 another in the same area as ecological succession proceeds. This 

 situation presents difficulties when we attempt to arrange communi- 

 ties in some sort of order since any practical classification is based 

 on descriptive considerations such as the life form of the dominant 

 species or their position in the terrain. The presence of some types 

 of communities is more strongly influenced by climatic factors than 

 edaphic factors, but for other types the reverse is true. 



Studies of the arrangement of communities in hierarchies have 

 been made chiefly in environments where plants hold the dominant 

 position in the biocenose. It is not surprising then that common sys- 

 tems of classifications are based primarily on the vegetation. We shall 

 describe the chief units into which communities are grouped, but 

 unfortunately complete agreement does not exist as to terminology. 



Community Type 



Communities of a certain dominant life form, such as deciduous 

 forests, coniferous forests, and the like, obviously compose recogniz- 

 able categories. Some authorities, like Tansley (1939), regard any 

 mature community of distinctive life form as a "formation," but other 

 authorities, following Clements (1936), apply this term to climax 

 communities only. Extreme difficulty is often experienced in ascer- 

 taining whether the vegetation in a given region has attained its 

 climax condition, and for many types of investigation it is not neces- 

 sary to do so. Also there seems little logic in using a different term 

 for, say, grassland that is climax and grassland that is on its way to 

 becoming forest. When the state of ecological succession is known, 

 a modifier may be used for clarity by referring to the community as 

 a climax formation or a serai formation. Until general agreement on 

 usage is reached, it will be necessary to specify the particular sense 

 in which the term formation is used on each occasion, or to avoid it 

 by referring to the life form of the dominant organisms or to the 

 community type. Thus we may state that the vegetation in a certain 



