Origin of Biomes and Succession 



267 



pared with productivity charts (Fig. 118), it seems evident that 

 the chmax condition did not develop until a moderate amount of 

 growth had accumulated, in short, until the subclimax species had 

 changed the ecological nature of the area to some minimum degree. 



r 2 



3 - 



S 2 - 



I - 



16 28 46 



60 

 Ooys 



93 115 155 238 335 



Fig. 118. Growth of diatom-s in Silver Springs, Florida, A, under poor growth 

 conditions, and B, under excellent growth conditions. The histograms represent 

 the total productivity of all species combined in units of mass; the lines of num- 

 bers represent the highest number of species occurring at each time interval. 

 (Data from Yount, 1956.) 



In terrestrial communities the substrate may be modified to an 

 unusual degree during the various stages of succession, as in the 

 colonization and later community development on sand dunes in 

 the eastern deciduous forest (Fig. 119), and the covering of small 

 northern lakes through the famous sphagnum bog series (Fig. 

 120). In this bog series the sphagnum moss grows out from the 

 shore over the water; on this floating moss mat herbs and shrubs 

 grow, making a second community; after this growth has attained 



