Timber Sales in Selection Forests 87 



(e) Occasionally local markets demand all the timber 

 available to them, rendering a sale for the purpose of supply- 

 ing distant markets a bad policy. 



(f) If a prospective purchaser will take only a desirable 

 species in a mixed stand while inferior usable species are re- 

 fused, silviculturally the stand might be injured from such a 

 cutting ; therefore the sale should be postponed until a purchaser 

 is willing to cut a portion of the inferior species. 



2. The choice of the silvicultural system of management for 

 securing regeneration and involving the severity of the felling 

 is logically the next consideration. The Forest officer has ordi- 

 narily to choose from the three systems, or their modifications, 

 namely, Selection, Compartment Under Shelterwood, and Clear 

 Cutting. 



3. The rotation should be next determined, in order that 

 the diameter limit may be determined from a diameter-age 

 table. The matter of choosing the rotation can be approached 

 from several angles, all of which may influence the final choice. 

 One may assume that dominant trees should not be retained 

 after they fail to make an annual growth equivalent to a certain 

 percentage of their volume. To illustrate: ft may be assumed 

 that dominant trees not making the following growth in volume 

 shall be considered mature and subject to removal unless 

 silvicultural reasons intervene : In the Rocky Mountain Region 

 on Quality I sites, 2 per cent; on Quality II sites, 1^2 per cent; 

 on Quality III sites, 1 per cent. The purpose for which the 

 timber will be used may be another view point; fuel or ties, 

 for instance, can be grown under a shorter rotation than saw 

 timber. Since the Government can best afford to sacrifice finan- 

 cial considerations its forests are usually managed with long 

 rotations, especially where the forests serve primarily as protec- 

 tion against soil erosion and for water conservation. Western 

 Yellow Pine stands are being handled in the Northwest with a 

 rotation of 150 years, and Engelmann Spruce requires as long 

 a time, or longer in most localities, when grown for saw timber. 

 Schneider's formula,* rate of growth equals 400 divided by the 

 number of rings in the last inch multiplied by the diameter at 

 breast height outside the bark, is a convenient method for deter- 

 mining the rate of growth of trees which are nearing maturity. 



*More accurate results are obtained by using 450 in case the trees are 

 near maturity, 500 for medium aged trees and 600 for rapid growing trees. 



