DIAMETER GROWTH IN EVEN-AGED STANDS 59 



for other purposes it may be more convenient to average before plotting, especially 

 when a large number of trees are used. In this case rule a large sheet of paper so 

 that there will be one vertical column for each age from one year to the age of the 

 oldest tree. Record the radius measurements in their proper age columns, average 

 and finally even off by means of a curve. 



Method of Procedure.— (Using method of plotting before averaging.) 



1. Ages in this case are the independent variables, diameters the depend- 



ent variables; hence, lay off the cross-section paper with ages ui 

 ten-year periods on the abscissa axis, and diameters in inches on the 

 ordinate axis. Label. 



2. Before plotting the values from any analysis sheet it should be checked 



according to the instructions for the tallyman, Problem 7. If it 

 does not check do not use it. All data in this book supplied for use 

 with this problem have been checked. 



3. Determine the respective values of the points to be plotted as follows, 



and plot them accordingly : 



(a) The successive diameter values by multiplying the radius measure- 

 ments, as recorded, by 2. 



(6) The age corresponding to the first radius measurement is taken as 

 recorded in the upper left-hand corner of the space allotted to 

 the first decade. The succeeding ages are determined by adding 

 10 years to the age of the first decade for the age of the second 

 decade, and 10 years more for each successive decade; or the 

 age at any decade is equal to: [(No. of the decade minus 1) 

 times 10] plus number of years in the first decade. This, 

 however, gives the age at the stump and not the total age of 

 the tree; hence, in order that our study may be based on the 

 total age, it will be necessary to add also the number of years it 

 took the tree to grow to stump height. The formula then 

 becomes: The total age for any decade measurement equals 

 [(No. of the decade minus 1) times 10] phis the number of years 

 in first decade plus the number of years required to grow to 

 stump height. During the actual process of plotting it is neces- 

 sary to determine this value only for the first point to be 

 plotted. The values (ages) of the succeeding abscissae can be 

 determined very rapidly by simply adding ten years to each 

 preceding value. 



4. When all the values are plotted average for each ten-year period as 



follows : 

 (a) The average ages: By averaging separatelj', in a horizontal 



direction, all plotted points in each ten-year period, letting 



to 10 inclusive represent the first period, 10.1 to 20 inclusive 



the second, and so on. 

 (h) The average diameter: By averaging separately, in a vertical 



direction, all points in each age period as in (a). 



