336 PLANT SOCIOLOGY 



VII. Euchamaephyte seres. The climax in steppes of the warmer region with 

 mostly alkaline soils and in cold unfavorable regions on mostly acid 

 soils (dwarf -shrub heath, etc.) (Fig. 170). 



VIII. Shrub seres. Shrubby climax communities often lie just above the tree 

 line on mountains, forming a shrub zone. They are also found in the 

 north and in hot, dry regions as a transition between steppe and desert 

 (low scrub). Chaparral, Chamaerops scrub, garigue, and sibljak of the 

 Mediterranean climates are not climaxes but rather transition societies 

 (Figs. 144 to 146). 



IX. Forest seres. The natural terminal stage of vegetational development 

 in the temperate, warm, and torrid zones is forest, whenever the water 

 supply is sufficient. 



In naming and defining seres one may use the especially striking 

 phenomena of the course of succession, based upon the habitat (moor 

 seres, snow-soil sod seres, solo7itschak-shruh seres, dune-forest seres, 

 subarctic moss seres, equatorial forest seres, etc.) or upon the nature of 

 the succession (land-forming, sod-forming seres, etc.). Our knowledge 

 of the dynamics of vegetation is still far too scanty, however, to permit 

 more than a preliminary outline of the above group of seres. 



5. History (Synchronology) of Vegetation. — Of the rise and decline 

 and the genetic relation of prehistoric plant societies very little can be 

 said, owing to the lack of adequate fossil records. Paleontological 

 research, be it ever so carefully executed, can give at best only frag- 

 mentary cross sections, momentary glimpses, of a floristic sequence of 

 inconceivable duration. These glimpses follow one another with little 

 continuity. The sequence is interrupted by enormous breaks, during 

 which climate and habitat may have suffered many changes. The few 

 fossil beds we have give only rarely an imperfect picture of a definite 

 plant community. All too often the fossil remains have been washed 

 together from far and near or collected by the wind or (in the latest 

 Quaternary beds) brought together by man. It requires a good 

 imagination to reconstruct from such a jumbled mixture of species a 

 definite association or to tell its genetic sequence. Of course, we must 

 not ignore the fact that the indicator value of the species, as expressed 

 by fidelity, may be available for synchronological uses. 



Synchronology is better handled as a branch of syngenetics, to 

 which it is obviously closely related, rather than as a subject by itself. 

 We have then the study of present-day changes in vegetation, on the 

 one hand; and secular (Christ, 1879; Gams, 1918) or paleogenic suc- 

 cessions, i.e., paleosyngenetics, on the other. 



The investigation of moors and peat bogs has yielded considerable 

 information for the most recent geologic period, the Quaternary. 



