834 JOURNAL OF FORESTRY 



If it is considered that the virgin timber of the United States will all 

 be logged off in 60 years, and figuring a rotation of trees on the average 

 as 130 years, then under this plan of 20-year return and cutting one- 

 third the volume (basal area) each cut, the virgin forests of the 

 country are immediately placed upon a sustained yield basis. The indi- 

 vidual property may not be in this condition, but it will be true, con- 

 sidering the forests of the United States as a whole. 



Furthermore, by cutting only one-third the basal area (which prac- 

 tically equals the volume, at least after the first cut), overstocked forests 

 are reduced in stocking, and understocked forests are automatically 

 built up. 



Illustrations of the way that the regulation by area with volume check 

 works out with stands of different stocking, follow : 



One-third of the volume is cut every 20 years. 



Assume a rotation of 120 years. This will be too long for some sec- 

 tions of the country, and too short for others. On the average, how- 

 ever, it will lessen or increase the volume obtainable but very little. 



Volume of stand per acre 10,000 board feet 



Growth per acre per year, average acre 200 board feet 



Rotation 120 years 



Period of return 20 years 



First felling — 



Ys of 10.000 (1921) 3,333 feet 



Second felling — 



i/i of (10,000 — 3.333) plus growth. 



Growth in 20 years is 20 X 200 — 4,000 



— 1/3 (6,667 plus 4,000) 



— ^ of 10,667— (1941) 3,556 feet 



Third felling 



— ^ of (10,667 — 3,556 plus growth) 



— Ys (7,111 plus 4.000) 



— Ys (11,111) — (1961) 3,704 feet 



Fourth felling — 



— Ys (11,307) — (1981) 3,704 feet 



Fifth felling— 



— Ys (11,538) — (2001) 3 846 feet 



And so on, the amount of the fellings gradually approaching the 

 amount of the growth, as the growing stock is built up to approach 

 normal. 



Take the example of a heavy overstocking : 



Volume per acre (average of forest) 40.000 board feet 



Growth per acre per year (average acre) 250 board feet 



Rotation 120 years 



Period of return 20 vears 



