24 ELEMENTARY FORESTRY. 



grower cannot rely upon such methods, because they are too. 

 expensive or entirely impracticable. He may indeed plow for 

 his first planting and cultivate the young trees, but after a few 

 years cultivation will become impossible and the effects of the 

 first preparation will be lost. He must therefore attain his 

 object in another way, that is, by mulching the soil. The 

 shading is done at first by planting very closely, so that the 

 ground may be protected as soon as possible from sun and wind. 

 The shade should be maintained well throughout the life of the 

 tree, even if more planting is necessary to accomplish it, and if 

 in later life the trees get thin in the tops or die out, it may 

 become necessary to plant underbrush to protect the land. 



Undergrowth in Forests may be rather injurious in pre- 

 venting the proper development of young trees, but it is gen- 

 erally very beneficial in retarding evaporation from the surface- 

 soil, in retaining the snow in the spring and in killing out grass 

 and weeds. 



Forest Floor is a term used to indicate the mulch on the 

 ground in forests. This is made up of the fallen twigs and 

 leaves which remain on the ground, where they slowly decay 

 and form a cover of rich mould or humus. This protective 

 covering serves a most useful purpose; it permits the rain and 

 snow waters to penetrate the soil without at the same time mak- 

 ing it too compact, thus keeping the soil granular so that the 

 air can enter, and in the best condition for conducting water, 

 while at the same time it prevents washing away of the land and 

 too rapid or excessive evaporation from the surface; the humus 

 is also an active agent in aiding decomposition of the mineral 

 substances in the soil. 



Subsoil. Tree growth is less dependent on the condition of 

 the surface soil and more dependent on the subsoil than is the 

 growth of agricultural crops. For instance, in the case of drift- 

 ing sand overlying a moist subsoil, it has been found that where 

 pains are taken to get the young trees started they will often 

 do well although such land is poorly adapted to agricultural 

 crops. There are many acres of land in Minnesota and Wis- 

 consin that have such conditions, and they should seldom be 

 entirely cleared of trees. 



"Washing of Soils. The soils most likely to wash badly 



