STAND GRAPHS IN LIMITATION OF CUT 721 



urements show that there are 7,800 b. f. of merchantable timber above 

 12 inches d. b. h. per acre, which is divided between black jack and 

 yellow pine, as indicated. If all of the yellow pine were removed and 

 all of the black jack retained it would result in the cutting of 89 per 

 cent and a retention of 11 per cent of the stand. Obviously, the amount 

 of timber retained per acre would be relatively low. To retain all of 

 the larger black jack and to cut all of the thrifty yellow pine might 

 be silviculturally undesirable.- Let us therefore assume that all of 

 the black jack above 22 inches d. b. h. should be cut and that all of the 

 yellow pine below 22 inches should be retained. Measurement on the 

 graphs shows that 73 per cent of the volume and 92 per cent of the 

 number of black jack would be retained. Likewise, measurement on 

 the graphs shows that 9 per cent of the volume and 29 per cent of the 

 number of yellow pine trees would be retained. The total amount 

 retained per acre is therefore computed as follows : 



Black jack . . 850 X 0.73 = 620 b. f . 

 Yellow pint G950 X 0.09 = 625 b. f. 



Total 1245 b. f.= 15.01 per cent of total stand. 



If this particular stand were marked to the diameter limits indicated, 

 an approximate retention of the corresponding volume would be 

 secured. Conversely, the diameter limits to which timber should be 

 marked in order to retain a given volume per unit of area can be 

 ascertained. 



MODIFICATION OF METHOD FOR SFLEfTION SYSTFM OF CUTTING 



In stands where strict cutting to a given diameter limit can be fol- 

 lowed, the method outlined should be very feasible. Where a selection 

 system is practiced, however, as in the yellow pine ty])e of the South- 

 west, some modification is necessary. The following is therefore 



suggested.^ 

 I 



"Since marking in the yellow pine type involves a selection system, both black 

 .jack and yellow pine are often retained, regardless of diameter class. 



'This example is merely cited for illustration and is not necessarily the limit 

 desired. Moreover, owing to the fact that a selection system is [)racticed, other 

 diameter classes and a different volume per acre would result. The modifica- 

 tions necessary to meet the demands of a selection system are discussed under 

 a corresponding caption. 



