266 Origin of Biomes and Succession 



COMMUNITY SUCCESSION 



If life should be removed in some way from a particular ecological 

 setting, certain types of communities would colonize the denuded 

 area, then be succeeded by others, until finally one community 

 would appear to persist indefinitely. The early communities in this 

 succession are termed subclimax communities; the last stage is the 

 climax community. 



A simple example of succession occurs on abandoned dirt roads 

 in the east-central United States. The bare soil is colonized first 

 by annual grasses such as Aristida; within a year or two perennial 

 herbs and grasses such as Andropogon invade the area, crowd out 

 further growth of Aristida, and form a solid sod; after a few more 

 years shrubs and small trees such as Rubiis and Sassafras become 

 established, gradually crowd out the Andropogon and convert the 

 area into a low-canopy community; and still later larger tree spe- 

 cies such as Fraxintis gradually replace the shrubs and begin a 

 series of tree communities ending in a beech-maple (Fagus-Acer) 

 or oak-hickory ( Querciis-Hicoria ) climax . community. This entire 

 development may occur in fifty to a hundred years. 



Many examples of succession have been described for plant com- 

 munities ( Shelf ord, 1913; Park, 1949), but in many instances in- 

 vestigators disagree on the exact course of succession in a particular 

 area. Certain disagreements involving forest communities have 

 been pointed out by Baker ( 1934 ) who observed that two simple 

 reasons explain much of the difficulty: (1) the exact course of 

 succession may be different locally or regionally depending on 

 numerous ecological variables, and (2) our observations either 

 lack the necessary detail or have been made over too short a time 

 span to afford an adequate knowledge of many succession series. 

 The general theory of succession, however, is well substantiated 

 and raises some interesting points concerning the evolution of com- 

 munities. That time alone is not the controlling factor in succession 

 has been demonstrated by the observations of Yount (1956). He 

 measured the growth of diatoms in Silver Springs, Florida, con- 

 trasting the results from areas giving poor diatom growth with 

 those giving excellent growth. He found that early stages of suc- 

 cession were characterized by having a diverse diatom flora of 20 

 to 25 species whereas the climax condition had less than 12 species. 

 In areas of high productivity the climax condition appeared in 

 forty-six days but in areas of low productivity the climax did not 

 develop for over two hundred days. When these times are com- 



