so DETERMINATION OF THE INCREMENT. 



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

 interpolation. 



Generally, graphic interpolation gives the better results, as 

 it equalises accidental irregularities. In this case the abscissae 

 represent the ages and the ordinates the corresjDonding 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. 



J). Height Tnrremmf 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 

 already falling, 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 (say 

 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 Fast. 



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 

 two measurements. The latter are made with the calliper, 

 care being taken to mark the place of measurement without 

 causing an unusual swelling at that part of the tree. Where 

 immediate results are required, the increment can be ascertained 



