206 WILLIAM S. COOPER 



II. THE BOG SUCCESSION 



In the course of the Bog Succession mosses first appear upon 

 the sedge mat. Here they are of little importance, Scorpidium 

 scorpioides (L.) Limpr. being the only one occurring commonly 

 with the sedges. With the invasion of the sedge mat by the 

 various species of Sphagnum a new stage is inaugurated in which 

 the moss element is immensely predominant. Sphagnum does 

 not appear abundantly in all of the Isle Royale bogs, and its 

 abundance or practical absence in a given locality determines 

 which of two diverging lines the succession in that locality will 

 follow. If sphagnum is abundant, the principal bog shrubs that 

 accompany it will be Chamaedaphne and Ledum, and th^bog trees 

 that follow the shrubs, tamarack and black spruce. If sphag- 

 num is practically absent, the shrubs will be Chamaedaphne and 

 Alnus incana, and the bog tree, tamarack, with or without arbor 

 vitae. The causes of this divergence were not determined with 

 entire satisfaction. One factor was observed however that un- 

 doubtedly plays a part: the composition of the sedge mat. In 

 those bogs where sphagnum is abundant the dominant sedge 

 was commonly found to be Carex limosa, a soft low growing 

 species, producing no shade to' speak of and offering little resist- 

 ance to the spread of the moss. In bogs practically without 

 sphagnum the sedge is Carex filiformis, growing in tall dense 

 closely placed stools, which shade the ground between them and 

 offer effective resistance to the horizontal spread of the sphagnum 

 masses. The presence of Ledum and black spruce depends upon 

 the previous occupation of the ground by sphagnum. 



The contest between the sphagnum and the plants which pre- 

 cede and follow it is an interesting one. The sedges, especially 

 Carex limosa, after having been practically buried by the moss, 

 succeed for a time in holding their own by upward elongation, 

 keeping pace with the vertical growth of the sphagnum. The 

 same is true of the shrubs Chamaedaphne and Andromeda, and 

 a number of other species (fig. 4). Individuals growing appar- 

 ently upon the moss can nearly always be traced downwards to the 

 substratum. Sooner or later most of these fail in the competi- 



