82 YIELD TABLE STUDIES 



(b) Normality ran also l)o determined, and that often more rapidly by 

 comparing the basal areas of all plots of the same age and site 

 cjuality without curves as follows: 



1. Determine the average total basal areas of plots of same 



average age. 



2. Plots whose areas do not fall within 7.5 per cent of this average 



are discarded. 



3. Average the plotted points of each site quality separately, even 



off with a regular curve, read ofT the average volume per acre in 

 10-year periods, and arrange in table form. 



4. In addition to the yield the Normal Yield Table should also include 



the following information for each 10-year age period : 



(a) The average height; 



(6) The average diameter (D.B.H.); 



(c) The number of trees per acre; 



(d) The total basal area in acre terms; 



(e) Sometimes also the form factor and the growth per cent. 



All of the above are determined just as they were in Prob- 

 lem 34, except that stands not normally stocked are not in- 

 cluded and all calculations are made separately for each site 

 quality. 



C. References. — Numbers 71, 74 and 86. 



D. Discussion. 



1. Name in the order of procedure all the important steps necessary in 



the collection of data for the construction of a Normal Yield table. 



2. What other factors beside volume may be used to determine normality 



of stocking? Under what circumstance would it be more advan- 

 tageous to use a different factor? 



3. What factor beside volume may be used to determine site quality by 



Bauer's Method of Bands? 



4. What would be the chief difference in the collection of data for Normal 



and Empirical Yield Tables? 



5. Outline briefly the main steps in the method of procedure for collect- 



ing data for a yield table thinned for the first time in late life. 



6. Outline briefly a method of procedure for a yield table for mixed 



stands, assuming that we have an even-aged stand of Douglas Fir 

 with an under-story of hemlock. 



PROBLEM 40. (Field.) Method of Using Yield Tables in the Field. 



Explanation. — Yield tables are used to show the future returns from planta- 

 tions and immature stands, for estimating, for the determination of site 

 quality, and, with reference to working i)lans, the growing stock, the normal 

 yield and the rotation. That the students may work this exercise out prac- 



