348 PAST succession: the ceneosere. 



a lower life-form, and finally terminates in tmidra. Such a change from higher 

 to lower life-forms might properly be termed regressive, and, as was pointed 

 outinChapterVIII,theterm "regression" might well be applied to the replace- 

 ment of a climax, such as deciduous forest, by a series of preclimaxes, such as 

 coniferous forest, scrub, and tundra. In view of the misleading use of "regres- 

 sion" in the development of the sere, it is perhaps imdesirable to use it in 

 connection with the climax changes of cliseres. For thdfee who wish to dis- 

 tinguish cliseres upon the basis of direction, the clisere which proceeds from 

 lower to higher climaxes may be termed a postclisere, and that from higher to 

 lower a preclisere. 



Cosere- — ^In its simplest form the cosere is a sequence of two or more seres 

 on the same spot. It is best seen where the plant remains of the constituent 

 seres are well-preserved, as in peat-bogs. In the great majority of cases the 

 sere does not produce a distinct stase, and the cosere does not persist in the 

 form of a tangible record. In this event the cosere still represents a basic 

 process in succession, but one which can be followed only by tracing the 

 development of one sere after another. Within a particular climax the cosere 

 consists normally of a primary sere with a varying number of secondary seres. 

 Thus, after a prisere had produced a grassland or forest climax on glacial till, 

 this climax would tend to persist until a climatic change produced a shifting, 

 except in areas denuded by flooding, fire, etc. In these, secondary seres might 

 occur repeatedly, and thus give rise to a cosere. Such a development is best 

 understood in the case of peat-bogs, since prisere and subsere are preserved 

 in their successional relations. A peat-bog may also exhibit more than one 

 prisere, in cases where the first has reached its climax and the latter has been 

 destroyed by flooding which produces an open body of water. This second 

 prisere may follow the first directly, after a climax period of variable length, 

 or one or more subseres may intervene. Theoretically, the cKmax will reappear 

 in the cosere several to many times, and this is usually the case. In some areas 

 repeated fires, for example, may destroy the community in various develop- 

 mental stages, and thus hold the succession in a precHmax almost indefinitely. 

 This is well illustrated in the lodgepole-pine forests of Estes Park in northern 

 Colorado (Clements, 1910 : 9). About the base of Long's Peak fires seem to 

 have occurred at least 11 times from 1707 to 1901, and most of them over the 

 same area to some extent at least. As a consequence, no subsere has been 

 able to reach the climax of Picea engelmannii and Abies lasiocarpa during the 

 past 200 years, though the control of fires now promises to make such an 

 outcome possible. 



The cosere will show a series of climaxes whenever the shifting of zones 

 characteristic of the cliseres enters the situation. Before the advent of man 

 secondary disturbances were much rarer than at present, and the cosere of a 

 glacial period must have consisted largely or wholly of priseres with successive 

 climaxes. Here again the course of events can be well seen only ia the records 

 of glacial coseres furnished by swamps and peat-bogs. If the shifting were 

 relatively rapid, all the climaxes of the chsere might be superposed upon the 

 prisere. Ordinarily it is more probable that each prisere after the first ended 

 in successive preclimaxes as the ice advanced, and in successive postclimaxes 

 as it retreated. The probable details of such coseres are considered under the 

 Pleistocene period. 



