14 



A PRIMER OF FORESTRY. 



them will be full of knots, and its value will be small. 



If, on the other hand, the trees stand too closely 



tog'ether, although their 

 trunks will be tall and clear of 

 branches, they will be small 

 in diameter, and for that 

 reason low in value. With 

 the right amount of growing 

 space, trees grow both tall 

 and of good diameter, and 

 their trunks supply lumber 

 of higher price because it is 

 wide and clear. 



THE YIELD OF A FOREST. 



Fig. 6.— a white cedar which has 

 had too much growing space. 

 The tree is large, but full of knots, 

 and will yield very little good 

 lumber. 



One of the central ideas of 

 forestry is that the amount of 

 wood taken from any healthy 

 forest and the amount grown 



bv it should be as nearlv equal 



as possible. If more grows than 



is cut, then the forest will be 



filled wnth overmature, decaying 



trees; but if more wood is cut 



than is grown, then the supply 



of ripe trees will be exhausted, 



and the value of the forest will 



decline. To make the cut equal 



to the growth does not mean 



that the volume of wood grown 



each year on every acre should be cut from that acre, 



but that the total growth of all the acres, for one or 



Fig. 7.— Old rees which have 

 had the right amount of 

 growing space to make 

 clean trunks and clear 

 lumber. Germany. 



