266 Studies in Forestry [CHAP. xn. 



produced would be so good as that which may now be grown 

 without any such artificial stimulation. 



Soil that is exposed to the action of sun and rain is apt to 

 become rapidly heated, whereby the process of humification is 

 hastened on ; and, at the same time, the upper layer is apt to 

 cake or harden, whilst its nutrient salts are washed out into the 

 lower soil, in consequence of which the surface-soil deteriorates. 

 The best safeguards against such unproductive conditions are 

 undoubtedly the retention of a good normal canopy overhead, 

 and the prevention of the removal of dead foliage from the 

 ground either by wind or by any other means. 



IV. The Manner in which the Quantity of Moisture 

 in the Soil may be affected by the Methods of 

 Treatment of Woodland Crops. 



Unless care be taken to preserve the most advantageous 

 quantity of moisture throughout the soil, the productivity of 

 the latter becomes greatly prejudiced. For if, on the one 

 hand, too much moisture be allowed to remain in the soil, 

 this remains cold and inactive, the process of humification is 

 retarded, the solutions of the nutrient salts are weak and thin, 

 and the vital activity of the individual trees is below what it 

 otherwise would be if the soil-temperature of the layers per- 

 meated by the root-system were higher; and, on the other 

 hand, when there is an insufficiency of moisture throughout 

 the soil reached by the roots of the trees, the mineral food- 

 supplies, though perhaps contained potentially in a far greater 

 quantity than requisite for even the most exacting kinds of trees, 

 are often not available in that soluble form in which alone 

 they can be utilized by timber-crops. The former condition, 

 implying excess of moisture, can often be remedied by drain- 

 age, or by the choice of kinds of trees for crops like Alder, 

 Ash, Willow, Maples, Elm, and in a less degree pedunculate 

 Oak, Birch, Aspen, Larch, Spruce, and Weymouth Pine, all 



