VOLUME INCREMENT ON CUT-OVER PULPWOOD LANDS 615 



r(\sultant influence on distribution of wood in the tree bole will require 

 specific study for each species to finally settle the degree of accuracy 

 of diameter accretion measurements made at breast height. Studies 

 of complete stems following a logging operation will not bring out 

 this relation unless a cutting has taken place previously and has caused 

 sudden acceleration of the stand. Check of height on diameter will 

 give sufficiently accurate results if diameter increment measurements 

 are applied to local volume tables. 



USE OE GROWTH DATA 



Similar growth measurements for a given species may be arith- 

 metically averaged and plotted by diameter classes from a common 

 zero base line as shown in figure 1. This will bring out most strongly 

 the irregularities due to errors, as well as the comparison of growth 

 of the inch class. 



Since the final purpose is the determination of volume increment for 

 a fixed period of years, it is necessary to have a continuous growth 

 curve which can be read to any year and fraction of inch. The curve 

 shown in figure 2 is plotted directly from values in figure ]. The 

 14.7 years shown in figure 1 is the growth period required for a 4-inch 

 tree to become a 5-inch tree. This time was plotted on the 5-inch 

 co-ordinate in figure 2. The fifteen years required by the average 

 5-inch tree to reach (5 inches as shown in figure 1 was added to 14.7 

 years and the resulting 29.7 years was plotted on the 6-inch co-ordinate. 

 The other values for the curve were computed in a similar way and 

 plotted. The resulting curve represents neither the diameter growth 

 of a single tree nor the average for the stand through the period of 

 years shown, but shows the contemporary growth of all diameter 

 classes for a short period up to the time of measurement. 



This method of determining the diameter increment of any inch 

 class dithers from that used by Stetson (6) and Chandler (2), since 

 one measurement only is made on each tree, and the growth predicted 

 for any inch class is that actually attained by the next higher inch 

 class. It has the advantage of not carrying forward any error due 

 to difference in growth rate between the last half-inch of radius and 

 the last inch of radius, due to suppression or release cluring that period. 

 It assumes a stabilized rate of growth for at least an inch of diameter, 

 and is liable to error if projected too far into the future. 



