PLANT SUCCESSION 



219 



close growth in this zone serves to hold sediment, and the bulk 

 results in substantial accumulation of partially decomposed or- 

 ganic matter. When filling is sufficient, shrubs can survive on the 

 built-up soil. Finally, the soil will be firm enough and sufficiently 

 raised above the water table to support lowland trees, which may 

 eventually give way to a community similar to that of uplands. 

 This entire sequence can sometimes be seen as a more or less 



wm. 



FlG. 106 (B). Shrub stage of rock succession, mostly Rhus copallina here. 

 Note fringe of Andropogon, smaller herbs, and finally mosses at periphery 

 (upper). Tree stage (lower) on an old mat, forming an island on bare rock. 

 Oak-hickory forest in background is growing on shallow soil overlying 

 rocks. 186 



