270 Origin of Biomes and Succession 



ing on areas in the early stages of succession either will not germi- 

 nate, or the seedlings die (Went, Juhren, and Juhren, 1952). Seeds 

 of subclimax species falling in the climax area have the same fate. 

 However, when the organisms growing in one of the subclimax 

 communities have either added sufficient humus to the soil, or 

 produced sufficient shade, or brought about some other critical 

 effect, then the progeny of the organisms in the next successional 

 stage can reproduce and grow better than those of the community 

 occupying the area. This change then eliminates that particular 

 subclimax community in that area. In abandoned farm roads, for 

 example, the bare soil itself is perfectly suitable for growing the 

 climax trees if shade is added, as is done artificially with canopies 

 in raising seedling stock of forest trees. 



Billings and Mark (1957) pointed out that in subclimax grassy 

 "balds" the climax may be slow to colonize the subclimax but 

 ordinarily will do so eventually. Baker (1934) cited a similar ex- 

 ample involving great areas of aspen woods in Colorado which 

 persist because seeds of the usual coniferous dominants disperse 

 short distances. Hence, the true climax must "inch in" around the 

 periphery of the aspen woods. This is truly a slow process. The 

 ultimate in delayed succession occurs on certain Great Basin balds 

 in which subclimax grass communities have become virtual cli- 

 maxes because no seed source is available for Pinus ponderosa, 

 the normal climax dominant in that area (Billings and Mark, 1957). 

 In this instance local conditions cause a normally subclimax com- 

 munity to become a temporary climax because that community is 

 the final one which succeeds others in that particular area. 



These examples of temporary climax communities emphasize that 

 dominant species of the grass bald and aspen subclimax com- 

 munities are perfectly able to maintain themselves indefinitely if 

 not subjected to competition from dominants of the true climax 

 for that area. In other words, the subclimax community does not 

 have some finite time limit after which it disintegrates. Its domi- 

 nant organisms persist until better-adapted organisms crowd them 

 out. 



Aquatic Succession 



Fresh water and marine communities are strikingly different from 

 terrestrial communities regarding succession. In both aquatic hab- 

 itats, if an area is denuded it is replaced rapidly by the same com- 



