THE DEVELOPMENT OF COMMUNITIES 



333 



Photographs taken from the same point from time to time form 

 admirable records of the changing physiognomy of the vegetation. 



6.8 6.7 6.6 6J 6.V 6J 6.2 6.1 6.0 5.9 5.8 5.7 5.6 5.5 S.^pH 

 Fig. 168. — Curve of the characteristic species and the succession from the Elynetum 

 to the Curvuletum. Single stands Nos. 2-12 in Table 4, p. 70, arranged according to 

 pH of the soil solution. Each dot or circle represents a single stand. (After Braun~ 

 Blanquet and Jenny.) 



Curve Diagrams. — By means of curves it is possible to express 

 clearly the change in certain groups of species along with changes in 

 such determining factors of the habitat as light, moisture, lime content, 

 and acidity (Frey, 1927, 1928). 



Scrub ■ 



^ Pinus __ 

 sfrobus-foresf 



MiKed 

 foresf 



Acer saccharum- 

 climax foresf 



6piraea iomeniosa 



— — Juniperus communis 



Corylas rosiraia 



Hamamelis virginiana 



Viburnum ainifollum 



Taxus canadensis 



Fig. 169. — Change of frequency of six important shrubs in the course of a secondary 

 succession. {After Cooper.) 



Succession curves are especially adapted for precise expression of 

 the floristic and ecological changes which take place during the develop- 

 ment of an association. As an example, we cite the development of the 



