62 GENERAL GROWTH OF STUDIES 



may often be avoided by using a distinct color for all points, 

 curves, figures, and labels belonging together. 



(6) Plot values of D.I.B. (ordinates) on D.B.H. (abscissa) for each 

 tree as recorded on the Tree Measurement Blank. Select the 

 trees, so that they will be well distributed over the various 

 diameters. D.I.B. values can be obtained from Data Series III 

 by doubling the last radius measurement. 



(c) Average; draw a curve. Label this "Curve II (Ratio Curve)." 

 It may cross Curve I. 



3. These two curves now show the relationship between growth at D.I.B. 

 • (stump) and D.B.H. on age. The D.B.H. for any age may be 



determined as follows: 



(a) Beginning on the abscissa axis at the desired age, trace the per- 

 pendicular at that point to the point where it crosses the D.I.B. 

 curve (Curve I). 



(6) From this point trace the horizontal line straight across to the 

 Ratio Curve (Curve II). The line dropped from this point 

 perpendicular to the abscissa axis will indicate the D.B.H. for 

 the age started with. Show by dotted line and arrrows on the 

 cross-section sheet how this reading is obtained. 



4. It is customary to draw a third curve representing growth at D.B.H. 



as follows : 



(a) On the same sheet of cross-section paper let ordinates as there 



laid ofT for Curves I and II now represent D.B.H., and ages as 

 established for Curve I abscissa;. 



(b) From Curves I and II read off the values of D.B.H. on age in 



10-year periods, as explained in 3, (a) and (h), and plot them 

 according to 4 (a) . 



(c) Even off by a curve. Call this Curve III. 



5. Read off two tables. 



1. Showing the diameters (D.B.H.) at different ages in 10-year periods. 



2. Showing ages for the different diameters (D.B.H.) in even inches. 



PROBLEM 29. (Office.) The Determination of Height Growth. 



Explanation. — The determination of height growth depends upon the prin- 

 ciple that the number of annual rings at any point along the bole of the tree 

 represents the number of years it took the tree to grow from that point to 

 the tip. Thus the total age represents the number of years it took the 

 whole tree to grow from the ground to the tip, and the number of rings at 

 any cross-cut the number of years to grow from that point to the tip. In 

 order to find how many years it took the tree to grow from the surface of the 

 ground to any point intermediate between it and the tip subtract the number 

 of annual rings that occur at the desired point from the total age. 



Illustration 1 —To construct ;i T;i))lo of Ileighl Growth for Eirn-df/cd Stands. 



