titative relationships of the same species. In either case there is a 

 change in dominants. Within a given region the sequence of 

 dominants tends to be the same. The increase in complexity may 

 be manifest in increased layering of life-forms and greater stature 

 of the dominants. This is related to an increased mass per unit 

 area, or standing crop, and usually to greater production of 

 matter per unit area. It is questionable, however, if the final stage 

 in succession always has a greater standing crop than preceding 

 stages. Actual development of the community and modification 

 of the habitat are probably on an intracommunity basis. They 

 consist of directional change sequences on smaller areas within 

 the community. The individual small area of development and 

 change may differ in character from the surrounding parts of the 

 community. These changes on the more minute areas may be 

 completed before the replacement or change of the whole com- 

 munity has run its course (Figure 5-3). 



This directional change usually has a starting point and a 

 terminal point, which is the climax vegetation. For example, the 

 hydrosere may consist of the submerged, floating, reed-swamp. 



Figure 5-4. Primary succession on sand and gravel; first 

 invaders are club-moss {Selaginella underwoodii), stonecrop 

 (Sedum stenopetalum), Talinum parviflorum, and prickly 

 pear {Opuntia sp.). Early invading grasses are Bouteloua 

 gracilis, Poa rupicola, and Koeleria cristata. Virginia Dale, 

 Colorado. 



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