578 



THE COMMUNITY 



photosynthetic productivity continues, and 

 is increasingly affected by climatic fluctua- 

 tions, until the lake is filled with sediment. 

 Then (4) in cold temperate regions, where 

 lake basins are poorly drained, a mat of 

 sedges and grasses, or sphagnum moss, 

 develops as the initial "terrestrial" serai 

 stage. Tliis mat has a higher photosynthetic 

 productivity than the senescent lake, and 

 IS succeeded by a bog forest (5) dominated 

 by such trees as larch {Larix laricina), 

 spruce {Picea mariana), and arbor vitae 

 (T/tM/'a occidentalis) or their equivalents. 

 This bog forest may persist for a long time, 

 as an edaphic clirnax, or is succeeded by 

 (6) the regional, climatic climax forest. 



Another aspect of the sere has developed 

 from a study of periodic activities within 

 the community. In the discussion on diel 

 periodicities (p. 562) it was suggested that 

 community efficiency increased as the 

 nocturnal and diurnal components tended 

 to equalize one another. This increasing 

 utiUzation of the space-time lattice tended 

 to produce a symmetrical, and hence 

 arrhythmic, activity total with respect to the 

 twenty-four hour diel cycle. Degree of total 

 activity symmetry, then, becomes a measure 

 of complexity, and we would expect the 

 more pioneer serai stages to be more asym- 

 metrical, in terms of total diel periodism, 

 than the later serai stages. In other words, 

 it has been suggested that symmetry of 

 total community activity increases from 

 pioneer to climax (O. Park, 1941a). 



Development and succession may be 

 altered by natural, catastrophic events such 

 as forest fires caused by fightning, storm 

 winds of high velocity, earthquakes (p. 

 130), and so-called tidal waves. Not enough 

 attention has been given to the biological 

 consequences of such agencies in primary 

 communities. Recently Macdonald, Shep- 

 hard, and Cox (1947) have discussed the 

 tsunami in general terms. 



A tsunami is a long-period gravity wave, 

 in an ocean, that is caused by a sudden 

 large displacement of the sea bottom or 

 shores. A tsunami is accompanied by a 

 severe earthquake, and both are caused by 

 the same crustal displacement. The tsunami 

 of April 1, 1946, was the most destructive 

 in the history of the Hawaiian Islands. It 

 was generated by a sudden shift of sea 

 bottom in the Aleutian trough. Waves 

 traveled southward to Hawaii at an average 

 speed of 490 miles an hour, with an average 



wave length of 122 miles, and a height 

 over the ocean of about 2 feet. The initial 

 effects on Hawaii varied notably at differ- 

 ent points along the shores. At some places 

 waves smashed 50 feet above sea level and 

 carried half a mile inland. Locally, flooding 

 was accompanied by severe erosion of sand 

 beaches, and inland soils were eroded and 

 deposited elsewhere. Under such conditions 

 there would be much initial damage to the 

 marine Httoral, the strand, and a variety of 

 inland communities. The effects of such 

 damage on succession and development 

 have yet to be investigated, but it is obvious 

 that these processes would be deflected, 

 arrested, or temporarily altered. 



Less spectacular natural agencies may 

 alter succession and development. For ex- 

 ample, Albertson and Weaver (1946) re- 

 ported that a centuries old, ungrazed prairie 

 of mixed grasses in north-central Kansas was 

 reduced by drought and dust to a dischmax 

 of short grasses in a relatively short period 

 of time. 



So far, this chapter has been devoted to 

 development and succession under rela- 

 tively unmolested conditions, that is, with 

 primary sequences. Theoretically, this is a 

 valuable exercise, which, in reality, seldom 

 takes place under present, man-dominated 

 habitats and circumstances. Much of de- 

 velopment and succession is altered by mau, 

 and many seres are initiated, deflected, 

 arrested, or controlled by his activities, or 

 those of his domesticated plants and 

 animals (Fig. 216). These are known as 

 secondary sequences, in the sense of 

 Warming (1909), Tansley and Chipp 

 (1926), Woodbury (1933), Clements and 

 Shelford (1939), among many students 

 who have examined the effects of civifized 

 man's interference with the serai course of 

 events. These primary and secondary se- 

 quences often have been discussed as 

 priseres and subseres, respectively, by 

 students of the successional process. 



Space limitations prevent adequate treat- 

 ment of secondary seres, or subseres." 



* The following references will serve to open 

 the literature on secondary seres: Bennett 

 (1949), CampbeU (1946), Ellison (1946), 

 Johnson (1945), Gustafson et al. (1947), 

 Hesse, Allee, and Schmidt (1937, Chap. 28), 

 Korstian (1937), Larson and Whitman (1942), 

 LeBarron and Neetzel (1942), Oosting (1948), 

 Osborn (1948), Pearse (1939, Chap. 14), 

 Rummell (1946), Vogt (1948). 



