22 BOTANICAL GAZETTE [JANUARY 
abundant in such situations than the balsam. Its growth under 
the same conditions seems to be somewhat faster, however, and so 
the few birches of the windfall area, or some of them, soon overtop 
the balsams and cause the suppression of many of the latter, at the 
same time, with the aid of the balsams, temporarily preventing 
further reproduction of either species. Paper birch has com- 
paratively few and ineffective fungus enemies (DANA 18) and is 
not particularly susceptible to damage by wind, on account of its 
elastic branches and extensive though shallow root system. Even 
when it is broken off in severe storms, as occasionally happens, it 
has a means of recovery in its ability to send up vigorous sprouts 
from the stump. Occasional clumps of immense birch sprouts 
scattered through the forest are evidence of this power. The most 
effective obstacle to its increase is competition with the balsam 
in its early stages, and here its greater rate of growth gives it a 
slight but important advantage. On the whole it may be said with 
certainty that its low birth-rate is compensated by a very low 
mortality, and it is thus able to maintain itself in making a good 
proportion of the mature stand (figs. 4, 5). 
PICEA CANADENSIS (white spruce).—This species is ecologically 
much less important than the first two, occurring only sparingly 
in most places; but it attains a greater size than the other trees, 
and is one of the most conspicuous features of the forest. On 
account of its scarcity little could be discovered concerning its 
life-history upon Isle Royale. From the few seedlings that’ were _ 
observed it seems probable that abundant light is necessary for 
its successful reproduction. According to the United States Forest 
Service (22) it is not a prolific seed bearer, and has definite seed 
years, which in New England are about eight years apart. All the 
young trees seen were growing in situations where at least fairly 
abundant light was available: It seems probable therefore that the 
white spruce is also largely dependent upon windfalls for its suc- 
cessful reproduction in the virgin forest. It is able to withstand 
severe winds without breaking, as is shown by individuals towering 
conspicuously above the general forest level. It is not particularly 
liable to fungus injury. Birth-rate and mortality are both low, 
and the species is able to maintain its small proportion in the forest. 
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