CHOICE OF SPECIES IN ARTIFICIAL REGENERATION 35 



direct seeding on soils which quickly lose moisture from the sur- 

 face layers. On the other hand, beech, maple, elm, and red gum 

 are comparatively shallow rooted in early life and cannot be 

 safely seeded on dry or leachy soils in the open. They can be 

 reproduced much more readily under an overwood or on clay soils. 



23. The Composition of the Soil in Relation to the Choice of 

 Species. Although no soil is wholly devoid of any one of the 

 chemical nutrients necessary to support tree life, sometimes some 

 of them are present in such limited quantities or in such large 

 amounts that they do not sustain nutrition and growth. In 

 regions of adequate -precipitation, however, conditions which bring 

 about a dearth in mineral nutrients available for tree life usually 

 cause a deficiency in available soil moisture, and it is to the latter 

 rather than to the former that poor growth is attributable. 



The demand for mineral nutrients varies somewhat with the 

 species. Hartig has shown that spruce produces much more 

 timber than beech in proportion to the amount of the various 

 mineral constituents absorbed from the soil. Many of our hard- 

 wood species, as illustrated in beech, maple, and yellow birch, are 

 particularly rich in ash elements and require a larger amount of 

 mineral nutrients in the soil than most conifers, particularly pine 

 and spruce. The former species should usually be confined to soils 

 rich in mineral nutrients, while most conifers will succeed on soils 

 relatively poor in these materials. Many soils too poor to produce 

 a profitable crop of oak, beech, maple, or other trees which de- 

 mand a fertile soil can be made to yield a fair return when seeded 

 or planted with less exacting species like white and red pine. 



Lime is of great importance in improving the physical con- 

 dition of most soils. Although not directly essential for the 

 nutrition of the tree, it is endured in small quantities by most 

 species. It is harmful to many species when it appears in con- 

 siderable quantity in solution in the soil water. Beech and maple 

 thrive on soils rich in lime, while chestnut and many pines, spruces, 

 and firs are excluded or do poorly upon them. 



24. HUMUS IN ITS EFFECT UPON THE CHOICE OF SPECIES. As 

 humus has both a direct and an indirect influence upon forest 

 growth, the relative amount in the soil influences the selection of 

 species. The rapidity of early growth in forests established by 

 seeding or planting is very largely dependent upon the presence 

 of a certain amount of humus. The vigorous growth of young 



