‘ 
’ 
1913] COOPER—ISLE ROYALE 23 
OTHER TREES.—Pyrus americana (Marsh) DC (mountain ash), 
though fairly common, is of little importance ecologically, since it 
is very short-lived, never reaches any great size, and produces little 
shade. Its life history in most respects is similar to that of the 
birch, and it has the same habit of producing sprouts from the 
stump. Pinus Strobus L. (white pine) is scattered thinly through 
many parts of the forest, generally towering high above the other 
trees. Its ecological status seems to be similar to that of the white 
spruce. There is no indication that in recent times at least it has 
ever been abundant upon Isle Royale. Picea mariana (Mill) BSP, 
Larix laricina (DuRoi) Koch, and Populus tremuloides Michx., 
which are found here and there in the climax forest, will be sufh- 
ciently treated in connection with quadrats 5 and 6. Populus 
balsamifera L. also occurs sparingly. 
TAXUS CANADENSIS.—The most important of the lower plants 
of the forest—more important indeed than many of the trees—is 
the ground hemlock. Its influence lies in the completeness with 
which it occupies and shades the ground, preventing tree reproduc- 
tion over large areas. This effect will be noted in connection with 
quadrats 5 and 6, and quadrat 1 includes part of a ground 
hemlock area in which trees are practically absent. Taxus can 
endure considerable shading, but is never found in the dense shade 
cast by the balsam groups. Balsam in its turn is excluded from 
large areas by Taxus, so that the competition between these two 
species is exceedingly keen. Taxus spreads abundantly by under- 
ground stems, and in this way invades new areas of forest when 
conditions are favorable, at the same time dying out in the older 
portions of the growth, thus allowing other plants to start in such 
places. 
Ill. QUADRAT STUDIES 
The method of investigation whereby a knowledge of the dynam- 
ics of the forest was gained was as follows. A rectangular area was 
laid off, made up of one or more units of 5 m. square, the usual 
size being a quadrat of 10 m. square, or four units. In the diagram 
of this area the position and kind of every tree, down to the smallest 
seedling, was plotted and its diameter noted. Cuts were next 
made with an ax to the centers of the large trees, and the small 
