AMERICAN SYLVICULTURE 



The productiveness of agriculture depends, above all, on the 

 chemical qualities of the soil tilled. A crop of trees, on the other 

 hand, takes from the soil but little, since the tree consists mainly 

 of C, 0, H, or since wood is nothing but air solidified by sunshine. 

 The phosphates, nitrates and potash absorbed by the tree are 

 returned to the soil by the fall of branches, leaves, seeds, flowers, 

 etc. 



The traces of chemical fertility locally removed in the shape 

 of logs are, in addition, counterbalanced by the decomposing influ- 

 ence on the rock exercised by roots, root-bacteria, and enzyms. 



Hence it is not likel}' that a rotation of crops, such as is 

 required in agriculture, has any advantages in the case of forestry. 

 In primeval vpoods, we know that Nature allows a species to 

 succeed itself. It must be admitted, howeverj that a short-living 

 crop of weeds (fire cherries, aspens, briars, herbaceous weeds) 

 intervenes frequently between successive generations of trees. 



The physical qualities of the soil preeminently influence the tree 

 species and the rate of its growth. The chemical qualities of the 

 soil play the most potent role in the case of agricultural species. 



Soil fit for agriculture is not necessarily a good forest soil 

 (prairies). Soil fit for forestry (strong North slopes) is often 

 utterly unfit for farming. 



XIV. Soil covers. 



Soil covers are either dead or living. Dead soil covers are 

 snow, debris of leaves and twigs. Living soil covers consist of 

 mosses, grasses, etc. 



After K. Boehmerle, a living moss-cover retards the growth of 

 young trees, during a dry season. The moss absorbs the larger 

 part of the precipitations. During .a wet season, the moss-cover 

 may be useful by storing the surplus of moisture. It seems advis- 

 able to remove the moss from the woods in rotations of about three 

 years. Compare C. G. F., 1910, page 523. 



Snow keeps the soil warm, prevents rapid changes of tempera- 

 ture, prevents young plants covered by it from perspiring, prevents 

 heaving of plants by frost. 



The debris on the ground feed millions of animals and fungi; 

 the}' harbor, on the other hand, mice, larvae and other enemies of 

 plant growth. Debris frequently prevent reproduction from self- 

 sown seed and increase the severity of forest fires. Living, as well 

 as dead soil covers, influence the evaporation of moisture, the 

 porosity of the soil and the drainage. 

 20 



