402 



Hoiv LiviiJg Things Affect One Another unit vti 



Fig. :i53 Clemi hm?bermg (left) reduces the fire hazard. Digging trenches (right) 

 to keep a forest fire jroin spreading, (u. s. forest service) 



water has been lost from the hillsides. 

 Fewer kinds of plants can grow on dry 

 than on moist hillsides. 



Forest conservation. We must con- 

 tinue to cut forest trees for necessary 

 lumber, but we must do it in such a way 

 that the forests will not be destroyed. 

 We must have conservation. About sixty 

 years ago, the United States Forest Serv- 

 ice was established as part of the Depart- 

 ment of Agriculture. Schools of forestry 

 were opened in many parts of the coun- 

 try; new professions, such as those of 

 forester and forest ranger, arose in con- 

 nection with this work. These men and 

 the biologists who studied forests have 

 learned many important facts. It takes a 

 forest tree between fifty and one hun- 

 dred years to grow to a size suitable for 

 making into lumber. The first rule of 

 conservation is to use only as much as 

 will be naturally replaced. This rule may 

 be applied as a simple arithmetic prob- 

 lem: the man who owns 50,000 trees 

 ready for cutting should cut no more 

 than 1000 every year. The trees to be cut 

 should be carefully selected. They should 

 be the older trees which provide good 



lumber or large quantities of pulp and 

 those trees should be cut that hinder most 

 the growth of smaller trees. If it is prop- 

 erly spaced, cutting in a forest is highly 

 desirable, for it gives the small trees an 

 opportunity for faster growth. You 

 should now be able to do Exercise i. 

 Some land now used for crops or pasture 

 is better fitted for forest growth. In some 

 such areas trees are being planted by the 

 Federal government, by the State gov- 

 ernment, or by well-informed private 

 owners. 



The soil problem. The problem of soil 

 destruction is one of the greatest that 

 faces the people of the United States. 

 Unfortunately, most of us do not know 

 about it. The best soil normally lies near 

 the surface, for here, over long ages, or- 

 ganic material from decaying animals 

 and plants has been collecting. This rich 

 soil is called topsoil. You have read how 

 the destruction of forests leads to the 

 rapid run-off of water from hillsides. The 

 topsoil is washed away. And what is left 

 dries up and is later blown away in enor- 

 mous amounts. Figure 354 shows how 

 serious the effects may be. 



