THE THEORY AND PRACTICE OF WORKING PLANS 105 



by method No. 4, the formula should be cut down to the first 

 one or two expressions of the series; e.g., if to the first ex- 



pression, then y= ?4H — =1.674+4.814 = 6.488 feet b.m. 



a4 — a.j cc 



per acre or, for the 1730 acres in this t>pe = 11,224 board feet 



of hemlock. 



The cutting cycle equals 04 — ^13 = 35 years. 



(c) Value and Application. — This method, first published 

 by Hufnagl in 1893,* is excellently adapted, especially in its 

 second variation, to the irregular and overmature selection 

 forest which is so commonly encountered in all parts of America. 

 It is especially well suited to virgin stands, tending to cut the 

 excess growing stock (of overmature timber) within the first 

 cutting cycle, and yet providing ample material for a second 

 cut at the end thereof. 



The data which are required are those of every thorough 

 forest survey preliminary to a working plan, namely, data on 

 diameter-class distribution, on number of trees in each (in 

 representative stands), of volume, and of diameter growth 

 or, in the first variation, of increment (current annual). If 

 it is not feasible to tally diameter classes for the entire tract, 

 carefully chosen, fully stocked sample plots of varying site 

 qualities will suffice, but when applied to the total stand must 

 be reduced to correspond with the average density of stocking. 

 All data should be revised at least once in ten years. 



When accompanied by a plan of cutting (distribution of 

 cut) for the next decade, the method is perhaps the most prac- 

 tical yet invented for irregular selection forests. Indeed, it is 

 intended for just such conditions in the more remote parts of 

 Austria. 



* " Oesterreichische Vierteljahrschrift fiir Forstwesen," 1893, pp. 177 and 

 following. 



