BIOTIC FACTORS 



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species to endure the active nitrogen compounds, various degrees of 

 nitrophily may be distinguished, and a whole series of floristically 

 related, more or less nitrophilous "animal resting-place communities" 

 may be recognized. These nitrophilous communities might very well 

 be taken as indicators of the capacity of the soil for nitrification. It 

 must not be forgotten, however, that where therophytes are not numer- 

 ous, communities once established have considerable endurance and 

 often maintain themselves in changed conditions. Since the establish- 



FiG. 143. — Yarding of grazing stock in the beech climax region of the Auvergne, 

 1,100 m. {Photo by Bador.) 



ment of the Swiss National Park (1911), the cattle yards there are no 

 longer in use as such. Nevertheless, the floristic composition of the 

 vegetation upon them has not changed in the least. The R. alpinus, 

 Chenopodium bonus henricus, and Aconitum stands have withstood 

 outside competition very well, even where the soil today has a strongly 

 acid reaction. 



Meadows are frequently fertilized for the improvement of the sod 

 by means of pasturing. The yarding of cattle, that is, a brief main- 

 tenance of cattle upon an enclosed area, is especially effective for the 

 improvement of the meadow with dung. The whole maintenance of 



