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THE SMALLER SOCIAL UNITS 25 



The sub-association is comparable to the subspecies and rarely has 

 its own indicator or characteristic species. Rather it is characterized 

 by "differential species" which, in other expressions of the association, 

 are absent, occur more sparingly, or are more poorly developed. 

 Naturally there cannot be a sharp distinction between the association 

 and the sub-association. 



The facies is distinguished wholly by differences in the quantity or 

 distribution of species, especially by the predominance of certain 

 companion species of the association. 



Facies and sub-associations are occasionally called elementary 

 associations, following Drude (1919). This expression it seems better 

 to avoid. 



Fragmentary Associations. — Every individual association, every 

 stand, must include the essential characteristics of the association, if it 

 is to rank as fully representative. Especially the normal characteristic 

 combination of species must be present. Bits of vegetation whose 

 membership in a definite association is beyond doubt, but which for any 

 cause have been hindered in their development or disturbed by external 

 agencies such as lack of space, unfavorable habitat, human or animal 

 intervention and therefore give only an incomplete picture of the 

 association, are called "fragmentary associations." A Carex curvula 

 sod with Phyteuma pedemontanum, Avena versicolor, Sesleria disticha 

 or a beech wood near a large city with only a few companion species of 

 the beech is a fragmentary association (Fig. 9). There are associations 

 which today occur solely as fragments or mere remnants. 



Settlement. — By the term settlement (Siedlung, Vegetationsfleck) 

 we may designate any small combination whatsoever of individual 

 plants, Avithout regard to taxonomic value or sociological status. A 

 stone overgrown with lichens or algae, a moor or a group of trees, are all 

 settlements. 



