144 MICHIGAN SURVEY, 1908. 



habitats produced by local influences tend to become transformed inta 

 the dominant biotic association or formation. In general also, small 

 bodies of water are rapidly encroached upon by inwash, vegetation or 

 drainage, and tend to become extinct and forested. All other openings, 

 as the rocky ledges and ridges or burns, are encroached upon as soil 

 accumulates or fires are prevented, and the forest biotic association 

 spreads over the entire area. 



From such relations it will be seen that our knowledge of the causes 

 and conditions of succession must largely result from the study of 

 these local enmronments or hahitats and their hiotic succession, because, 

 where dominance is established the succession is almost completely 

 obliterated. Each minor habitat and society is to he looked upon, as 

 simply a stage, more or less temporary, in the onward laave toward th<i 

 dominant or climax association. Thus in the marshes, birch or aspen 

 woods, rock openings and ponds may be "original" conditions which 

 are becoming cumulatively transformed in the direcltion of the final 

 dominance of the climax biotic type. 



The relatively slow rate of change in many environmental processes 

 and the relative stability of the climax biota,^ is doubtless the basis 

 for the current view that such conditions are relatively constant or fixed ; 

 but that change and not constancy is the normal and usual condition in 

 nature is quite evident upon a moment's reflection. Almost every one no- 

 tices these changes after an absence of a few years from a region. Thus 

 intimacy tends to blind us to changes unless a liahit of giving attention 

 to them is deliberately cultivated. For this reason some find it almost 

 impossible to recognize environmental changes or to comprehend their 

 significance. It is therefore of practical value to recognize clearly 

 under what conditions changes may be most readily perceived. There- 

 fore the importance of the studj' of local inUuences is emphasized, and 

 the necessity recognized of distinguishing the dominance of geographic 

 and relatively stable conditions or formations as contrasted with those 

 due to local and often relatively changeable conditions. Then among 

 these changes we must distinguish those which are mere fluctuations 

 and those which are indicative of the true progressive succession. 

 This is mainly accomplished by attention to general relations and the 

 subordination of minor details. 



5. Environmental and Associational Convergence. At the present 

 imperfect stage of ecological development, comparison must furnish us 

 the most important and general clues to the processes of succession ; and 

 undoubtedly this method must long remain as our main guide on ac- 

 count of its comprehensive application and the magnitude of the prob- 

 lem to be solved. It is therefore desirable that the limitations of the 

 method should be clearly borne in mind. It is often assumed that the 

 implied successions of a given place are the same as those which have 

 developed at that place in the evolution of the present climax. But 

 as we positively know that many different causes are able to produce 

 the same or very similar results, such conclusions must be received 

 with due caution. That the dominant geographic conditions tend to 

 override local influences seems very fairly established because (jlverse 

 local or original conditions are transformed into the climaoo or domi- 



1 For the migrations of climax societies, cf. Adams. '05, 



