322 PLANT SOCIOLOGY 



of the stages. If the course of succession shows small fluctuations 

 which do not justify the recognition of a distinct sere, we may speak 

 with Furrer (1922) of variant seres. Besides the variations due to 

 climatic, edaphic, and phytobiotic causes, there are geographic varia- 

 tions due to local differences of floristic composition, and cultural 

 variations due to cultural influences. 



The Caricetum firmae-Curvuletum meadow sere of the east- 

 central Alps furnishes an example of a relatively simple sere with three 

 variants (Table 36). 



This example, giving the development of vegetation on calcareous 

 gravel and talus of the alpine levels, shows that one sere may start 

 from several pioneer stages. Pioneer stages which are but little 

 differentiated floristically are often genetically related, as shown in the 

 table by horizontal arrows. 



Complete Seres. Partial Seres. — New land arises by upheaval, fall- 

 ing of water level, deposition of sand or gravel by wind or water or 

 by violent catastrophes such as landslides, volcanic eruptions, tidal 

 waves, or through human agencies. The existing vegetation is 

 completely destroyed. Regeneration begins with primitive pioneer 

 stages and runs through the entire developmental series ("complete 

 sere")- Complete seres are possible on new land of any kind. 



Many natural phenomena, like earthquakes, avalanches, brief 

 flooding, and many human activities, like clearing and fire, do not 

 completely destroy the existing vegetation. They cause retrogres- 

 sions, reversions, and delays. Regeneration in such cases begins not 

 with a pioneer stage as of new land but with a suitable stage of the 

 original sere. This results in a partial sere, which sooner or later runs 

 into the original complete sere, provided its development is not stopped 

 by man. 



Every complete sere leads to the climatic terminal stage, the 

 climax. 



Climax. — We have seen (p. 255) that development of vegetation 

 and formation of soil tend toward a definite end point determined and 

 limited by the local cHmate. The smaller the periodic variations of 

 climate and the longer a uniform undisturbed climate prevails the more 

 completely and extensively will this end point be realized. This 

 relatively permanent final condition we have called a soil and 

 vegetative climax. But the climax itself, it must be expressly stated, 

 is only a resting point, a breathing space in the ceaseless change of the 

 composition of vegetation. 



Permanent Communities. — Plant communities w^hich have not yet 

 reached the end point, the cHmax, and yet from whatsoever cause 



