36 
RELATION OF TREE GROWTH TO LIGHT. 
The first point is possessed in the highest degree by the evergreens 
and by those deciduous trees which have a dense foliage and preserve 
itdense through all time. There are not many of these latter, for a 
large number which in their younger years have a full foliage thin out 
with increasing age. Besides, by the suppression of the lower 
branches, which are not capable of living under the shade of the crown, 
the latter is removed farther and farther from the soil, and lateral 
crowding also kills out many individuals; so that with all this, sooner 
or later (according to species and soil conditions), the crown cover is 
more or less broken, and weed growth, rapid humification of the litter, 
and increased evaporation is the consequence; é. g., all the cottonwood 
plantations outside of the wet bottoms. The same deterioration of the 
soil will be noticed under the ash and the black walnut, which thin 
out rapidly. Soil conditions will, to be sure, modify this capacity of 
retaining a dense foliage, and on a fresh deep soil even the thinly-foli- 
aged trees will carry a fuller crown. 
It is a matter of observation that as a rule the trees which preserve — 
a full dense crown are the ones which are capable of thriving under 
shade, or at least with less light than the thinly-foliaged ones; thus, 
a yew, a spruce, a box elder, a beech, will thrive under shade where a 
pine, a birch, or a locust can hardly exist. There are some exceptions, 
and some of the thinly-foliaged trees, like the oak, can vegetate though 
not thrive under the shade of some “ foregrown” tree. In fact, one 
may, according to the different degree of light which is necessary for a 
thrifty development, range the species so that those at the top of the 
scale may be called light-needing and those toward the bottom shade- 
enduring. 
I do not want to be understood that any of our forest trees thrive 
better for being shaded. Excepting in their earliest stages, when pro- 
tection against heat and cold, rapid evaporation and transpiration, is 
needed by some, they all grow best in full enjoyment of sunlight; in 
fact, the rapidity of their development is proportionate to the amount 
of foliage which is at work, and this again depends upon the amount of 
sunlight at its difposal. But some can get along with less sunlight; 
they can endure without much detriment a more or less dense shade 
for a longer or shorter period, while others, under the influence of their 
own crown even, thin out soon, and, if shaded by neighbors, are ar- 
rested in their growth and killed sooner or later. The time when the 
influence of light conditions is most potent varies with different species 
and according to the site, so that, for instance, on a rich, moist soil a 
light-needing species like the birch will endure for a long time consid-— 
erable shade, which on a poorer soil would have proved detrimental. 
As arule you will not find among the undergrowth of our forests 
any species that is a light-needing one. Hence culling any of our 
