^ INCREASING THE YIELD. 41 



particularly such trees in thinned stands, have a wider crown spread than 

 is given. The maximum crown spread which can be obtained without un- 

 duly developing the crown at the expense of the clear length of stem 

 would be one-half more than is given. 



Breast-high Spread of Breast-high Spread of 



diameter of crown diameter of crown 



tree, inches feet tree, inches feet 



7 11 15 16.5 



8 11.6 16 17.2 



9 12.4 17 17.9 



10 13.3 18 18.6 



11 13.7 19 19.4 



12 14.4 20 20 



13 15.1 21 27.7 



14 15.8 22 21.3 



Pure stands. The maturity of pure, even-aged stands is determined by 

 the date at which the largest profit or per cent, is earned on the invest- 

 ment. The investment embraces 



(1) The value of the soil; 



(2) The cost of establishing the stand, which might consist either 

 in leaving seed trees, or increased cost of logging the old stand, or 

 the cost of seeding or planting; 



(3) The cost of protection, which may be a yearly cost or might 

 be required only while the stand was young, and the interest on such 

 costs ; 



(4) Taxes on soil and timber, and the interest on taxes; 



(5) The cost of thinning and cleanings and the interest on such 

 expenses. 



The volume of a pure, even-aged stand increases rapidly at first, then 

 more slowly and finally becomes stationary. The value of the timber 

 based on the quality or proportion of grades increases in the same man- 

 ner. Value increment continues long after the volume of the stand has 

 become stationary. 



There is also, as has been explained, a fluctuating increase in price of 

 grades of lumber, which affects the value of stumpage. This is neglected 

 in all calculations, but it should be given careful consideration by owners 

 of stands in fixing the period of cutting. Table 14 shows the cost per 

 1,000 board feet of growing yellow poplar in pure stands, and the most 

 profitable age at which to cut, when the cost of stocking is $3 an acre and 

 when the detailed items of expense are as shown. The greatest profit per 

 1,000 board feet, 49 cents, in excess of all costs and interest, is made by 

 cutting at 35 years of age. At 30 years the profit is 42 cents per 1,000 

 feet ; at 40 years it is 36 cents a 1,000 feet. Price increase is neglected. 



