ECOLOGICAL SUCCESSION OF MOSSES 



203 



been mentioned, is sometimes of considerable importance. It is 

 thus seen that the characteristic forest mosses become established 

 notably in advance of the forest itself. 



In cases where the xerophytic forest stage, characterized by 

 Pinus Banksiana and Picea mariana, intervenes, the under- 

 growth is practically a continuation of the heath mat, with the three 

 forest mosses, Calliergon Schreberi, Hylocomium proliferum, and 

 Hypnum crista-castrensis, gradually attaining dominance. In 

 early stages it is common to find a ground cover composed largely 



Fig. 2 Xerophytic forest near Amygdaloid Harbor. Cladonias (Cladonia 

 alpeslris, C. sylvatico, C, rungiferina) at right, invaded by Calliergon Schreberi 

 (dark mass at left). 



of cladonias, with practically no humus. In a slightly more 

 advanced condition Calliergon is gaining the upper hand and the 

 climax trees are coming in. Later still Hylocomium and Hypnum 

 are found disputing the dominance of Calliergon, and the climax 

 trees increasing at the expense of the jack pine and the black 

 spruce. When the climax state is attained the latter trees have 

 disappeared, balsam fir, paper birch, and white spruce are in 

 control, and the undergrowth is composed largely of Calliergon, 

 Hylocomium, and Hypnum in about equal proportions. 



