FORESTRY AND CONSERVATION 331 



While, as stated, all trees thrive best with a moderate and 

 even supply of moisture, some can get along with very little, like 

 the conifers, especially pines ; others can exist even with an excessive 

 supply, as the bald cypress, honey locust, some oaks, etc. The cli- 

 mate, however, must also be considered in this connection, for a tree 

 species, athough succeeding well enough on a dry soil in an atmos- 

 phere which does not require much transpiration, may not do so in 

 a drier climate on the same soil. In the selection of different kinds 

 of trees for different soils, the water conditions of the soil should, 

 therefore, determine the choice. 



Light Conditions. To insure the largest amount of growth, 

 full enjoyment of sunlight is needed. But as light is almost always 

 accompanied by heat and relative dryness of air, which demands 

 water from the plant, and may increase transpiration from the 

 leaves inordinately, making them pump too hard, as it were, young 

 seedlings of tree species whose foliage is not built for such strains 

 require partial shading for the first year or two. The conifers belong 

 to this class. 



In later life the light conditions exert a threefold influence on 

 the development of the tree, namely, with reference to soil condi- 

 tions, with reference to form development, and with reference to 

 amount of growth. The art of the forester consists in regulating the 

 light conditions so as to secure the full benefit of the stimulating 

 effect of light on growth, without its deteriorating influences on the 

 soil and on form development. 



As we have seen, shade is desirable in order to preserve soil 

 moisture. Now, while young trees of all kinds, during the "brush" 

 stage of development, have a rather dense foliage, as they grow older 

 they vary in habit, especially when growing in the forest. Some, 

 like the beech, the sugar maple, the hemlock, and the spruce, keep 

 up a dense crown; others, like the chestnut, the oaks, the walnut, 

 the tulip tree, and the white pine, thin out more and more, and 

 when fully grown have a much less dense foliage ; finally, there are 

 some which do not keep up a dense shade for any length of time, 

 like the black and honey locust, with their small, thin, leaves; the 

 catalpa, with its large but few leaves at the end of the branchlets 

 only, and the larch, with its short, scattered bunches of needles. So 

 we can establish a comparative scale of trees with reference to the 

 amount of shade which thev can give continuously, as densely 

 foliaged and thinly foliaged, in various gradations. If we planted 

 all beech or sugar maple, the desirable shading of the soil would 

 never be lacking, while if we planted all locust or catalpa the sun 

 would soon reach the soil and dry it out, or permit a growth of grass 

 or weeds, which is worse, because these transpire still larger quan- 

 tities of water than the bare ground evaporates or an undergrowth of 

 woody plants would transpire. Of course, a densely foliaged tree 

 has many more leaves to shed than a thinly foliaged one, and there- 

 fore makes more litter, which increases the favorable muJeh 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 



