22 BULLETIN 152, U. S. DEPARTMENT OF AGEICULTUEE. 
tioned are always scattered through these forests, and an extra 
abundance of one or more of them in mixture with hemlock may 
give rise to distinct local forest types. Among such species are white 
spruce, balsam fir, white and rock elms, basswood, paper birch, sweet 
birch, red maple, and black cherry. In the South, yellow poplar, 
shagbark and shellbark hickories, white, red, and post oaks, and 
cucumber often grow with hemlock in the coves, while black, scarlet, 
and chestnut oaks, pignut and mocker nut hickories, and chestnut are 
its usual associates on slopes and ridges. 
EFFECT OF LIGHT, SOIL, AND MOISTURE ON THE COMPOSITION OF 
THE STAND. 
The heavy foliage of hemlock adds greatly to the density of any 
stand in which the tree grows. Since it will endure a heavier 
shade than any of its associates, hemlock finds little difficulty in 
establishing itself under them, even when their crowns form a fairly 
dense cover. For this reason the forests of which it forms a princi- 
pal part nearly always contain trees varying widely in age and size. 
This is especially true when it grows in mixture with species like 
beech, sugar maple, spruce, and balsam, which are also shade enduring. 
Trees like white pine, which require more light than hemlock, can 
succeed in mixture with it only by growing more rapidly and to a 
larger size, thus keeping their crowns above or at least as high as 
those of the hemlocks. In mixed stands of white pine and hemlock 
there is usually a dense understory of the latter species, which is the 
only one able to establish itself in the shade of the crowns. In this 
way hemlock is able to creep into stands of pine and other species, 
and by its superior shade endurance gradually assume predominance. 
(PL III.) 
Under the particularly dense shade of hemlock and spruce stands, 
and in thickets of rhododendron and other heavy-f oliaged undergrowth, 
hemlock seedlings find it exceedingly difficult to survive, and the few 
which do survive grow with extreme slowness as long as the shade 
remains heavy. (Pis. IV and V.) When, however, light is admitted 
not too abruptly they rapidly recover from suppression. 
Hemlock is essentially a tree of fresh or moist soils ; in other respects 
its soil requirements are not exacting. In mixture with hardwoods 
it usually grows on loamy soils, ranging from sand loam to clay loam, 
rich in decayed vegetable material; and with white pine on sandy 
soils, well mixed with humus. Hemlock will grow on limestone soils, 
if not too dry, as well as on moist, almost swampy, loamy clays. 
Like all its common associates, it does best on deep, fertile, moist, 
but well-drained soils, where it and the hardwoods tend to crowd out 
the more light-needing white pine. 
