572 JOURNAL OF FORESTRY 



The reason why Von Mantel's formula gives such low results is 

 because it assumes that the actual growing stock is like the normal 

 growing stock for purposes of determining the cut, that is, since 



^'^nV = - th.eni= -7-, and letting F = nF,andF(the allowable cut) =t,then 



'2 



V . . r . 



3' = --. But the actual \ is not equal to --, since much of the stock is 



> r_ 4 2 



above rotation age, and the increment on these overmature trees is 

 usually less than that at rotation age. 



In the Catskills, the cuts determined by the Swiss method are close 

 to those obtained by the area check, although with the exception of 

 birch, more conservative. The cause of the low results obtained by 

 Von Mantel's formula has been explained. 



In Table 7, the second (preferred) variation of Swiss method will 

 be found to give slightly higher results. This is due to the fact that 

 the first (original) form of the method is merely a summation of the 

 current annual increment, while the second variation of the method 

 provides for the annual disposal of a certain amount of overmature 

 timber, during the first cutting cycle. The exception occurring with 

 the white pine and red pine results from the fact that there is consider- 

 able actual increment ("Zt") in the class of timber over the maturity 

 limit ("Z"). This increment "Zi" is not used in working out the 

 second variation of the Swiss method. The closeness of results ob- 

 tained with these two variations is noticeable with each species. Von 

 Mantel's method gives low results here, as it does in Table 6, and for 

 the same reason. Beech, maple, and hemlock show the largest differ- 

 ences, and it is in these species that the larger amounts of overmature 

 timber occur. In the other species the results are not so much at vari- 

 ance as in the species listed in Table 6. 



In forests of the kinds for which the two working plans were made 

 the use of Von Mantel's method would not be advocated except as a 

 check. Conservative results are always obtained, and where forests 

 are as abnormal as these, Von Mantel's formula is very likely to give 

 abnormal results. 



io«7= when wF=normal growing stock, r=rotation in years, and i=mean 

 annual increment. 



