AMERICAN SYLVICULTURE 



facilitate life to the tree itself and to its progeny. The production 

 of humns is the main source of that influence. 

 Governing factors are: 



A. Leaf canopy overhead. Evergreen as well as deciduous 

 woods return to the soil by the leaf fall annually a large amount 

 of dead matter readily assimilable. Shade bearers furnish a better 

 humus than light demanders, excluding, at the same time, intensive 

 insolation, so that the decomposition of the leaf carpet and the 

 evaporation of the soil moisture is favorably retarded. 



A hvunus formed by Beech, Maple and Chestnut is considered 

 especially good. Beech is called abroad, justly or unjustly, 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 gr-ound is destroyed frequently, 

 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 atmosplieric humidity. Usually the decomposition 

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

 leaves of the shade bearers decompose quicker than the heavy leaves 

 of the light demanders. The atmospheric moisture of high alti- 

 tudes causes an accumulation of large quantities of leaves. In the 

 tropics, there is little litter on the ground. 



C. Root system. 



It is the decaying root which allows the precipitations to trickle 

 down to the lower strata of soil. Hence tap rooters seem more 

 efficient than flat rooters in converting a rapid surface drainage into 

 a slow underground drainage. Decomposing the rock by chemical 

 action, the tap root foi'ces it to yield its soluble salts. 



D. Soil improvement through root-bacteria and fimgi. 

 The upper layers of forest soil are densely peopled with the 



hyphae of basidiomycetes, living on humus. Leguminous trees 

 (Locust, Kentucky Coffee tree, etc.) by their root-bulbs increase the 

 fertility of the soil, and the Alders seem to act in a similar man- 

 ner. On abandoned fields in Pisgah forest the soil is improved by 

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