18 ELEMENTARY FORESTRY. 



tree even if more planting 1 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 preventing 

 the proper development of young trees but it is generally 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 madeup 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 making 

 it too compact, thus keeping the soil granular so ihat 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 

 drifting sand overlying a moist subsoil, it has been found that 

 where pains is 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 are 

 those that are fine grained without much adhesive power, such 

 as fine sand and some kinds of clays. When, however, such 

 soils have a forest growth on them they are protected from 

 washing by the forest floor, tree roots and the humus in the 

 soil. Soils which contain large quantities of humus do not 

 wash much, since the particles of organic matter bind it 

 together; thus we find that newly-cleared timber land which 

 contains large amounts of humus may not wash much for a 

 number of years after the clearing and then commence to wash 



