80 DETERMINATION OF THE INCREMENT. 



centric rings are then counted at the end of each section, and 

 from the data thus obtained, the height of the tree at successive 

 periods of life can be ascertained, either by calculation, or 

 interpolation. 



Generally, graphic interpolation gives the better results, as it 

 equalizes accidental irregularities. In this case the abscissae 

 represent the ages and the ordinates the corresponding 

 heights. By connecting the points thus indicated by a steady 

 curve, the height at successive ages can easily be read off. 



Example. See analysis of a Scotch pine tree, at p. 83. 



b. Height Increment of the Future. 



The expected height increment for a number of years to 

 come can be estimated from the increment of the immediate 

 past. In doing this the rate of increment during the past 

 must be studied, and especially the time ascertained when the 

 current annual increment of the species usually culminates. 

 If the increment immediately before the time of inquiry was 

 still rising, it may continue to do so or not, according to 

 whether the maximum has been reached or not. If it is falling 

 already, it will continue to do so, and in that case the rate at 

 which it is likely to fall must be estimated. In this way the 

 probable increment for a limited number of years (10) can be 

 estimated with satisfactory accuracy. This is best done by 

 constructing a height curve of the past, and elongating it for the 

 required period so as to form a continuous curve. 



2. Diameter Increment, 

 a. Of the Past. 



This can refer to wood and bark, or to wood only. 



The increment of wood and bark laid on by standing "trees 

 can be ascertained by repeated measurements of the same tree, 

 a certain number of years being allowed to pass between every 



