DETERMINED BY AREA AND VOLUME. 235 



/•, and the last in the year r + m, then the rotation = r -\- 



and the mean annual cutting area = 



, m 



2' 

 A 



Example : — 



Let m = 20; then rotation = 110 years. Annual cutting 



1,000 



9"09 acres. Volume standing on an acre at 



110 



the age of 110 years = 6,690 + 334 = 7,024; hence annual 

 yield = 7,024 X 9*09 = 63,848 culnc feet. 



The intermediate yields would amount to = 35,010 cubic feet, 

 and : — 



Total annual yield = 97,558. 



The raising of the rotation has led to a reduction of the 

 volume yield, because the mean annual increment began to 

 decrease before the year 100. 



c. Scledion Forest. 



If all trees, which are cut in one year, \Yere brought together 



on a portion of the area, the latter should be = ^ : hence the 



yield is practically the same as in the case of clear cutting. 



Another way of looking at the matter is to determine the 

 area, on ^Yhich cuttings are made in each year ; this has been 



placed above (page 219), = -. • Everything, which has to be 



cut on this area, forms the normal annual yield. 



Example : — 



Area of a selection forest = 1,000 acres 

 Flotation . . . = 100 years 

 I . . = 20 years. 

 Then : 



A 1,000 Kn 

 - = .^ = 50 acres. 

 20 



