THE FOREST IN RELATION TO MAN 



383 



of the 500 native species in this country are worth growing from the 

 economic point of view. The red cedar grows very slowly ; the white 

 pine or the red oak could be grown in the same soil to great advan- 

 tage. We could replace the red spruce in New England by the 

 Norway spruce, just as many areas of France denuded by the Great 



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Fig. 200. Cutting trees to preserve forests 



The preservation of the forest does not mean simply to avoid cutting timber. By cut- 

 ting trees in zones at intervals of a number of years, and by thinning out the trees 

 where they are too crowded, it is possible to make a given area yield continuous crops 

 of wood. The zone a was cut first, then zone i>, and so on. By the time the last strip 

 has been cut. the trees on the first strip are well along, and thus a succession of cuttings 



may be continued indefinitely 



War, and other European regions, are being restocked with Douglas 

 fir imported from this country. We shall no doubt find foreign trees 

 better suited to our purposes in many localities than the native trees. 

 In the course of a number of years the rapid varieties will yield much 

 more timber than the others. But rapid growth is not of itself a de- 

 ciding factor, for it is necessary to consider the toughness of wood 

 and other qualities. The whitewood, or tulip tree, grows much faster 

 than the oak. but it can never be used as a substitute for the oak. 



423. Improving wood quality. Another improvement is being 

 brought about by the selection of varieties for quality. Without 



