SYLVICULTURE. 



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 and robt-bacteria. 



Hence it is not likely that a rotation of crops, as is required 

 in fields, has any advantages in the case of forestry. In primeval 

 woods, we know that Nature allows a species to succeed itself. 



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 good forest soil 

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

 utterly imfit 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. 



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

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

 lifting of plants by frost. 



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

 they 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 cover influences evaporation of moisture, porosity of 

 soil and water drainage. 



XV. Life in the soil (Compare Swiss L. F. F. 1904, May and 

 June). 



The soil lives like a plant or an animal, since it shows con- 

 tinuous changes of form and of composition. Very little, however, 

 is known of the life and the interdependence of millions of live indi- 

 viduals found in the soil. Certain it seems that tree growth is 

 bound on the presence of certain fungi and bacteria living on the 

 roots (Mycorrhiza). Most important are the bacteria capable of 

 digesting the nitrogen of the subterranean air. Leguminous plants 

 (Clover, Black Locust) are beset with root knobs, containing bacteria, 

 busily engaged in the assimilation of nitrogen. The. hyphae of a 

 fungus called Frankia play a similar role on the root knobs of 

 Alder and Sweet Fern. After P. C. Mueller, Spruce will grow on 

 poor sand lacking nitrogen if Pine is mixed with it, furnishing 

 nitrogen through its mycorrhiza. 



15 



