SYLVICULTURE. 



Tlie maximum number of bacteria is said to be found two ftet 

 below tlie surface of the ground, and none exist below six feet. 

 The number of bacteria per pound of soil varies from one hundred 

 million to two hundred aoid fifty million. 



Important, too, in plant ecology is the life of the larger anim.iN 

 (worms, insects, centipeds) changing the vegetable matter of the 

 soil into manure proper, mixing mineral soil and vegetable matter, 

 increasing the porosity, drainage and aeration and neutralizing the 

 acids of the soil. Shade, protection from wind and sufficient moistu.e 

 are beneficial to animal life in the soil. 

 Paragraph III. Influence of the sylva on the ecological factors. 



The influence exerted by tlie forest on local climate (heat, air, 

 precipitations, etc.) is dwelt upon in the lectures on forest policy. 

 Whilst the ecological factors shoA\n in tlie previous paragraph 

 exhibit the important influence which the soil has'on the tree, there 

 exists at the same time, although to a lesser degree, an influence 

 of the tree on the soil. This influence is invariably such as to facili- 

 tate life to the tree itself and to its progeny. The production of 

 humus is the main source of that influence. 



Governing factors are: 



A. Leaf canopy overhead. Evergreen as well as deciduous woods 

 annually return to the soil by the leaf fall a large amount of dead 

 matter readily assimilable. Shade bearers furnish a better humus 

 than light demanders, excluding, at the same time, intensive insola- 

 tion, so that the decomposition of the leaf carpet and the evaporation 

 of the soil moisture is favorably retarded. 



A humus formed by Beech, Maple and Chestnut is considered 

 especially good. Beech is justly called abroad the " Mother of the 

 Forest," owing to its soil-improving qualities. The leaf canopy is 

 particularly dense during the thicket and the pole-wood stage. Even 

 light demanders, whilst young, improve the fertility of the soil. At 

 a higher age, when the light demanders place themselves far apart 

 one from another (say less than 100 trees per acre), the humus on 

 the ground is destroyed, being replaced by a dense and impermeable 

 matting of grasses or shrubs. 



Amongst the conifers, Yellow and White Pine seem to furnish 

 the best humus. Spruce humus is too waxy. 



B. Rate of disintegration of leaves. 



This rate depends on insolation, on heat capacity of soil (sand 



versus clay), on atmospheric humidity. Uusually, decomposition of 



leaf fall takes place within two or three years. The thin leaves of 



the shade bearers decompose quicker than the heavy leaves of the 



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