216 PRINCIPLES OF AMERICAN FORESTRY. 



board measure, worth $3 = $18 per acre plus value of soil, 

 worth $5 per acre. 



2. The yield under forestry is 4,000 feet, worth $3 = $12 

 per acre to be derived at once, and 300 feet, worth 90 cents, 

 to be derived annually thereafter, being the annual produc- 

 tion of the 2,000 feet left standing, per acre. The future 

 yields are to be discounted at (x per cent. 2 per cent.). 



3. The annual expenses, under forestry, are 20 cents. 

 The extraordinary expenses are $4 per acre, spent at the 

 first cutting. 



90 20 



Equation: 18 + 5= 12+ Q () x _ ^ -^-*- 



Result: About 7 per cent. 



