Vegetation of Xorthern Cape Breton. 393 



this bn-ophyte ground cover in hindering evaporaticn and imped- 

 ing drainage, thereby influencing not only the moisture of the 

 substratum, but also its temperature, aeration, and toxicity, can 

 hardly be questioned. Usually the surface layer of living plants 

 is underlain by a more or less spongy mass of incompletely 

 decomposed vegetable remains (the duff), which commonly is six 

 inches or more in thickness. Corticolous liverworts and mosses 

 in general are much more poorly developed in coniferous than in 

 deciduous climax forests, although the lichens occupy a promi- 

 nent position, particularly the beard lichen {Usnea barbata), 

 which in well-lighted situations commonly drapes itself in grace- 

 ful festoons from the branches of the trees. 



Reproduction of the climax trees. — In his ecological investiga- 

 tion of the northeastern evergreen-coniferous climax forest, as 

 developed on Isle Royale, Cooper ('13, pp. 42, 43) arrived at 

 the following conclusions, which were based in large part on the 

 intensive study of carefully selected quadrats. For successful 

 reproduction the balsam fir requires abundant light, given 

 which it will germinate and thrive in any sort of situation. In 

 the forest, reproduction is practically confined to the openings 

 caused by windfall. "The forest is a complex of windfall areas 

 of differing ages, the youngest made up of dense clumps of small 

 trees, and the oldest containing a few mature trees with little 

 young growth beneath. The history of a windfall area is as fol- 

 lows. After the debris has disintegrated sufficiently to allow 

 abundant light to reach the ground, a new generation of trees 

 springs up, approximately even-aged, composed of the three 

 dominant species [balsam fir, white spruce, and paper birch], 

 Abies always greatly preponderant. During the continued 

 development of this group most of the individuals are at various 

 times eliminated, . . . Because of the dense shade no new 

 individuals can start beneath them and the final outcome is a 

 group composed of a few large trees, approximately even-aged, 

 in which Abies has nearly or quite lost its position of dominance 

 to Betiila." The resultant forest is thus "a mosaic or patchwork 

 which is in a state of continual change." Yet "the forest as a 

 whole remains the same, the changes in various parts balancing 

 each other." 



Turning now to northern Cape Breton, it would seem that the 

 ecological relations of the balsam fir here are somewhat different 



Trans. Coxx. Ac.\d., Vol. XXII 23 1918 



