Periodical Literature 109 



meets some difficulties especially in the absence of reliable normal 

 jrield tables. 



y 



The simplest short cut formula, as is well known is ns = -Xri, 



or .05 XrXri, i. e., the average increment at normal felling age 

 multiplied by the nimiber of stands in- the felling series and by 

 half the rotation. This formula is incorrect inasmuch as each 

 ageclass grows at a different rate as would appear from any growth 

 curve. It is only correct for one rotation, namely, the one in which 

 the deficiencies (deviation-s from i) of the first half of the rotation 

 are balanced by the excesses of increment in the second half, which 

 would, of course, be different for every species and site. To be 

 more generally correct, the formula should read ns = riXcr, in 

 which c is a variable constant. To determine this constant, normal 

 yield tables are necessary, which may be summed up by the well- 



known formula w5 = 5i+52+ • • +5r_i+— '' = 5, when, from 



S 



riXcr = S, c = — . The author has in this way calculated c 



nXr 



from a nimiber of yield tables for spruce, fir, pine, beech and oak, 



for various rotations and sites, and claims that for practical use 



and judgment the knowledge of c is of more value than the absolute 



amoimt of ns. The results are tabulated in various ways and 



cvirves for c are drawn, and these give at least interesting insight 



into the character of normal stock. 



First of all the tables show how very great the error of the 



formula can be, and even the correction to .45XrXn, which had 



been used for fir in the budget regulation of Baden is by no means 



satisfactory. For rotations from 80 to 120 years the values of c 



vary for spruce III site (Swiss mountains) from .464 to .554; for 



fir, from .327 to .472; for pine, from .548 to .691; for oak from 



.408 to .454; for beech, from .394 to .511. These values are based 



on total wood volume; figured for timberwood alone, the constants 



are considerably lower, owing to the fact that the stands attain 



timberw^ood size only from a certain ageclass, when the actual 



timber^^ood stock becomes relatively larger, so that a smaller 



value of c satisfies the formula. For the same positions as above, 



the ranges become then .392 to .508; .267 to .437; .454 to .596; 



.292 to .392; .316 to .428. 



