382 ELEMENTARY BIOLOGY 



and he cannot be expected to take into account effects a 

 hundred miles away or fifty years away. 



The Forest Service of the United States Department of 

 Agriculture has made many careful, scientific studies of forest 

 conditions and has thus been able to give sound advice on 

 the care and management of forests and wood lots from every 

 point of view. From these investigations we learn, first, the 

 importance of avoiding certain injuries to the forests, and, 

 second, the methods of increasing their value. 



For many years, toward the end of the nineteenth century, the 

 people of this country were using up trees about three times as fast as 

 they could grow. This meant that before very long we should have 

 destroyed all the usable trees and been practically without a suitable 

 wood supply. A scientific stud}- of the growth of trees in the forest 

 showed that it is possible to get all the wood we really need without 

 destroying our forest, if only certain principles are followed (Fig. 200). 



It is to be noted that the ordinary virgin forest is practically at a 

 standstill so far as growth is concerned. While new growth is con- 

 stantly takmg place, this is only enough to offset the death and 

 destrucrion among old trees. 



421. Increasing forest area. To meet the growing need for more 

 wood, it is possible to extend the forest area of the country. Areas 

 that have been cut and burned over may be reforested, and this 

 process is under way in many parts of the country. There is a great 

 deal of worn-out agricultural land and sand-dune land that would be 

 well suited to forests ; in many cases all that is needed is to protect 

 the young growth against fires. Another method of extending the 

 growth area is by fuller stocking of existing forest lands. Thus, some 

 trees are found growing so close together that they never become 

 thick enough to be of great value for timber ; but in other forests the 

 trees are so far apart that valuable space is allowed to go to waste. 

 By selecting trees suitable for a given region, and starting the young 

 plants rather close together, and then thinning out carefully, the 

 amount of timber grown on a given area can be greatly increased. 



422. Increasing wood yield. Another method for increasing the 

 wood supply is by the selection of varieties that will give a maximum 

 of growth in each forest area. It is likely that not more than seventy 



