THE ORIGIN AND GROWTH OF PLANT COMMUNITIES 591 



fungi, mosses, vascular plants have different modes of uptake, trans- 

 formation, storage, and decomposition. But we need to make much 

 finer distinctions if we are truly to understand the turnover within the 

 ecosystem. 



Replacement and encroachment. So much has been written about 

 plant succession that only the barest allusion to some of the review 

 papers can be made— for instance, Clements ( 1936 ) , Cain ( 1939 ) , Watt 

 (1947), Whittaker (1953), Dansereau (1956a). The matter of the 

 cyclic behavior of species, and indeed of entire communities, is very 

 much emphasized by Watt (1947), and I feel sure that it occurs at 

 various levels in the dynamic pattern, sometimes involving only a group 

 of pioneer stages, sometimes extending to the very climax ( Dansereau, 

 1956a, Figures 4, 5, 6, 7). The occurrence of cycle within cycle, or 

 rather of small cycles operating on the axis of a generally ascending 

 potential, has been demonstrated by Scui-field ( 1956 ) . Detailed mono- 

 graphs such as Jovet's ( 1949 ) and Dahl's ( 1956 ) provide the best pos- 

 sible test of these interpretations. They are unfortunately very scarce. 



The phytosociologists of the Ziirich-Montpellier school, on the 

 other hand, have long recognized initial, optimal, and terminal phases 

 ( Braun-Blanquet, 1932, p. 231 ) . Because of the prevalence of the phe- 

 nomenon of succession, they have been led to recognize, in each asso- 

 ciation, species which are constructive, conserving, consolidating, neu- 

 tral, or destructive. The presence of a number of species ( even more, of 

 a number of individuals ) considered characteristic of another associa- 

 tion can therefore be regarded either as showing a lag in the full de- 

 velopment of the association ( Clintonia borealis and Streptopus roseus 

 in the Aceretum saccharophori laurentianum ) or else the beginnings 

 of an invasion from another association (Betula poptilifolia in the 

 Solidaginetum laurentianum ) . 



Ordination of plant communities 



A full application of the criteria defined above to any single stand 

 of vegetation ( or to the synthetic tabulation of data from many stands 

 which defines the association), conveys a picture of what it is and of 

 how it functions. Should the communities be compared among them- 

 selves in the manner of organisms (whether or not one accepts the 

 idea of their being superorganisms ) , any classification will place some 

 of the characteristics listed herewith either above or below some of the 

 others, since all classification proceeds by subordination in that it 

 singles out some feature (morphological or functional or both) as 

 having more significance than the others. The various taxonomies to 

 which the plant world has been subjected demonstrate the many pos- 

 sible shifts in criteria. In the field of taxonomy, precisely, functional 



