14 
Hemlock is much more influenced by moisture conditions than by 
light, and it seeks northern slopes more because of their moisture than 
because of their coolness. In anumber of city parks where the Hem- 
lock is grown in isolated specimens as an ornamental tree the fact that 
it succeeds admirably in full sunshine is thoroughly established. So, 
too, isolated specimens of the flowering Dogwood, the Beech, and other 
shade-enduring species prove that these trees are able to endure shade 
better than their fellows, not that they thrive less well in full light. 
When trees of equal light requirement are planted together the 
struggle for light among them results in more rapid thinning than 
where light-demanding and shade-enduring species are mixed. If the 
single kind used be light-demanding, weeds and grass soon gain a foot- 
hold and rob the soil of much of the moisture which otherwise would 
be saved to the trees. Illustrations of this are common in the Cotton- 
wood plantations of the West. The Cottonwood is a thin-foliaged, 
light-demanding species, which does not shade the soil enough to pre- 
vent grass growth even where planted close. I have seen plantations 
of it in South Dakota where the trees were 40 feet high, and culti- 
vation was still necessary to keep the weeds down and conserve the 
soil moisture. 
In making a grove or plantation, varieties of different light require- 
ment should be mixed together, and varieties of equal light requirement 
should not be mixed. Illustrations of this law abound in wild growths. 
The Sugar Maple and the Beech are shade-enduring trees, and through- 
out the Northeastern States they will be found growing well in the 
shade of such species as White Ash, Black Walnut, and the Oaks and 
Birches. In even greater degree Hemlock is shade-enduring and is 
usually found as a lower growth, or ‘‘second story,” with White and 
Red Pine towering above. 
In the West the only native woods occur along the streams, and the 
difference in light requirement is less pronounced than in the heavily 
forested region. All trees there seem more intolerant of shade. Pos- 
sibly there are fewer cloudy days and the woods are more open, thus 
surrounding the trees throughout life with more light. But even in 
the Western woodlands a difference in light requirement is apparent 
and may be used advantageously by the planter. The Boxelder, Mul- 
berry, and White Elm withstand shade better than the Black Walnut, 
Green Ash, and Black Locust. The Red Cedar, White Fir, and White 
Spruce endure more shade than the Pines. 
The change in light requirement that comes with age is of great 
practical importance to the planter, as it enables him to provide shelter 
necessary in youth to certain species which are, nevertheless, intolerant 
of shade as they approach maturity. The Bur Oak is decidedly a light- 
demanding species, but during the first ten years it may be safely sur- 
rounded by dense-foliaged neighbors, and, indeed, it will be benefited 
for au even longer period by receiving light only directly overhead. 
