SHADE AND LIGHT REQUIREMENTS. 267 



quantities of water than the bare ground evaporates or an undergrowth of woody plants would 

 transpire. Of course, a densely foliaged tree lias many more leaves to slied than a thinly foliaged 

 one, and therefore makes more litter, which increases the favorable mulch cover of the soil. 

 Another reason for keeping the ground well shaded is that the litter then decomposes slowly, but 

 into a desirable humus, which acts favorably upon the soil, while if the litter is exposed to light, 

 an undesirable, partly decomposed "raw" humus is apt to be formed. 



Favorable soil conditions, then, require shade, while wood growth is increased by full enjoy- 

 ment of light; to satisfy both requirements, mixed planting, with proper selection of shade- 

 enduring and light-needing species, is resorted to. 



As the different species afford shade in different degrees, so they require for their development 

 different degrees of light. The dense foliage of the beech, with a large number of leaves in the 

 interior of the crown, proves that the leaves can exist and perform their work with a small amount 

 of light; the beech is a shade enduring tree. The scanty foliage of poplars and pines shows that 

 these are light-needing trees; hence they are never found under the dense shade of the former, 

 while the shade-enduring can develop satisfactorily under the light shade of the thin-foliaged 

 kinds. Very favorable soil conditions increase the shade endurance of the latter, and climatic 

 conditions also modify their relative position in the scale. 



All trees ultimately thrive best — i. e., grow most vigorously — in the full enjoyment of light, but 

 their energy then goes into branching. Crowded together, with the side light cut off, the lower 

 lateral branches soon die and fall, while the main energy of growth is put into the shaft and the 

 height growth is stimulated. The denser shade of the shade enduring kinds, if placed as neigh- 

 bors to light needing ones, is most effective in producing this result, provided that the light is not 

 cut off at the top; and thus, in practice, advantage is taken of the relative requirements for light 

 of the various species. 1 



The forester finds in close planting and in mixed growth a means of securing tall, clear trunks, 

 free from knots, and he is able, by proper regulation of light conditions, to influence the form 

 development, and also the quality of his crop, since slow growth and rapid growth produce wood 

 of different character. 



There are some species which, although light-foliaged and giving comparatively little shade, 

 are yet shade-enduring — i. e., can subsist, although not develop favorably, under shade; the oaks 

 are examples of this kind. Others, like the black cherry, bear a dense crown for the first twenty 

 years, perhaps, seemingly indicating great shade endurance; but the fact that the species named 

 soon clears itself of its branches and finally has a thin crown indicates that it is light-needing, 

 though a good shader for the first period of its life. Others, again, like the catalpa, which is 

 shady and shade enduring, as the difficulty with which it clears itself indicates, leaf out so late 

 and lose their foliage so early that their shading value is thereby impaired. Black locust and 

 honey locust, on the other hand, leave no doubt either as to their light-needing or their inferior 

 shading quality. 



That soil conditions and climatic conditions also modify crown development and shade 

 endurance has been well recognized abroad, but in our country this influence is of much more 

 importance on account of the great variation in those conditions. Thus the box elder, an excel 

 lent shader in certain portions of the West, is a failure as soil cover in others where it nevertheless 

 will grow. 



We see, then, that in determining the shading value as well as the shade endurance of one 

 species in comparison with another, with reference to forestry purposes, not only soil and climate 

 but also the character of foliage and its length of season must be" considered. 



As to shade endurance the more valuable species of the United States, including exotics, 

 may be classed as follows : 



Light-demanding from seedling stage: Aspen, cottonwood, black walnut, black locust, honey 



x This relation of the different species to varying light conditions, their comparative shading value and shade 

 endurance, is one of the most important facts to "be observed and utilized by the forester. European foresters have 

 done this, but since they had to deal with only a few species and over a limited territory, they could quite readily 

 classify their trees with reference to their shade endurance, and take it for granted that shade endurance and density 

 of foliage or shading value were more or less identical. With our great wealth of useful species it will be necessary 

 and profitable to be more exact in the classification. 



