66 PLANT SOCIOLOGY 



386, I). (The sole characteristic species which figures at all in the 

 curve at pH 5.8 to 5.5 is the preferential C. curvula.) The number cf 

 constant species is evidently not influenced by change in acidity; its 

 i;raph is a straight line. 



Similar curves showing the massing of characteristics in trie 

 optimum region are given by the Elynetum (see Fig. 168). 



Artificial interference with the ecology of the community quickly 

 drives out the characteristic species. If the Xerobrometum is manured, 

 the orchids, as well as Koeleria gracilis, Anemone Pulsatilla, PotentiUa 

 arenaria, Trifolium scabrum, and other characteristic species, disappear 

 at once, whereas the dominant grasses Bromus erectus, Festuca ovina 

 and many other constants may continue for a long time in spite of 

 heavy manuring. 



The characteristic species of the flat-moor associations react 

 similarly to a lowering of the water table; so also do the characteristic 

 species of forest comxmunities to the admission of light. 



The concept of fidelity has been used consciously or unconsciously 

 by many ecologists who do not employ the term. Thus Ilvessalo 

 speaks of the exclusive species of Finnish forest types, and Clements 

 parallels the concept in his plant indicators. 



If numerous characteristic species of an association reappear 

 together in another association of a far distant region, this proves the 

 ecologic relationship of the two communities. 



The moss-carpeted Picea sitchensis forest of Alaska, with Hylo- 

 comium loreuni, Aspidium spimdosum, Listera CGrdata, and Pirola 

 uniflora, as described by Cooper (1923), has undoubtedly similar life 

 conditions and exists under external relations similar to those of the 

 climax spruce forest of the Alps, where the same characteristic species 

 occur in the Piceetum. 



Syngenetical Indicators. — The narrow range of the characteristic 

 species and their resulting social specialization make it possible to use 

 their grouping in judging the stage of development of a plant society. 

 Our investigations in the eastern Swiss Alps (Braun-Blanquet and 

 Jenny, 1926) have shown that a maximum of characteristic species 

 goes with the optimum development of an association (cf. also Fig. 39) . 



In the progressive reforestation of the national domain in the high 

 Cevennes, the characteristic species of the Fagetum come in gradually, 

 exactly in proportion as the association approaches its original con- 

 dition. Only in the undisturbed high forest do M-e find their full 

 number and their highest development. 



From the comprehensive demonstrations of Linkola in Finland it 

 appears that Lycopodium complanatum,L.annotinum, Pirola chlorantha, 



