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attention to an important point in providing the proper light require- 
ment of trees in mixed planting. Such species as Boxelder and Rus- 
sian Mulberry, which endure more shade than most of the broad-leafed 
trees that have been tested in the West, by virtue of their compara- 
tively rapid height growth during the first few years, are especially 
useful as nurse trees, among which other species of more continuous 
height growth may be set. If the latter be light-demanding they will 
have overtaken their nurses before much damage can befall them (since 
all species endure somewhat more shade in infancy than when older), 
and if they be shade-enduring they will, by their habit of continuous 
growth, surpass their nurses and thus come into better light conditions 
as they develop. 
The shade endurance of trees is probably less in the plains than 
within the forest area. A list of trees most likely to succeed in the for- 
estless region, grouped with reference to their light requirement, is 
given below, the most light-demanding being named first. The rank- 
ing is only tentative, and further observations may modify it somewhat, 
but it is believed to be sufficiently accurate to stand as a basis for 
determining what species may be planted together: 
1. Cottonwood, Aspen, Mesquit, Black Locust. 
2. Scotch Pine, Austrian Pine, Rock or Bull Pine, Green Ash, White 
Ash, Black Walnut, Yellow Birch, Sweet Birch, Black Birch. 
3. Red Oak, White Oak, Bur Oak, Tulip, Pecan, Honey Locust, 
Chestnut. 
4, Jack Pine, Catalpa, Silver Poplar, White Elm, Black Cherry, 
Silver Maple, Osage Orange. 
5. Hackberry, Red Maple, Boxelder, Russian Mulberry. 
6. Sugar Maple, Beech, Norway Spruce, White Spruce, Douglas 
Spruce, Red Cedar, White Fir, Hemlock. 
Of these groups the first two may be considered lght-demanding 
trees, and the last two shade-enduring, leaving the third and fourth 
groups midway, but with considerable shade endurance in youth. 
In making selections from this list, hardiness and moisture require- 
ment must be kept in mind as well as light conditions and relative 
height- growth. 
MOISTURE. 
It has often been claimed that the absence of trees from the plains is 
attributable to a lack of sufficient moisture, and were it not that so 
many artificial plantations are growing in what was only a few years 
ago a treeless region, the hypothesis might be accepted. But when it 
is recalled, also, that even in the States of Illinois and Lowa, with an 
average rainfall of from 44 to 32 inches, vast areas were devoid of trees, 
the theory of itself will not stand. 
The minimum amount of moisture necessary for the support of forest 
growth can not be definitely stated, because other conditions can not 
20191—No. 18 2 
