37 



HILT plan a less exact method is admissible, particularly as regards 

 the younger crops, which must he surveyed over again when the 

 plan is revised. Hence for such crops a complete survey is seldom 

 necessary, and in the sample plots the method of rtoi {.height and 

 those based on tables of form-factors or of volumes or of yield may 

 be adopted. But where a certain degree of accuracy is required, 

 the method of survey by the average tree may be employed in 

 regular crops, a higher degree of accuracy being secured by the 

 establishment of girth-classes and the highest by U rich's 

 method, which is moreover the only one to adopt when it is re- 

 quired to estimate the yield in the various marketable classes of 

 converted wood. 



The establishment of height-classes gives a great deal of trouble 

 and extra woik. It should be avoided whenever possible, that is 

 to say, as often as the heights of the trees composing the crop do 

 not exhibit any marked irregularity. 



Chapter V. 



On the determination of the ages of trees and crops. 



The determination of the age of trees and of crops is a problem 

 which often presents insurmountable difficulties to the Indian 

 forester, since not only are the ring markings indistinct and 

 sometimes indistinguishable, but so many of our species form more 

 than one concentric ring of wood each year, and there is nothing 

 to prove that in their case the number, of rings is one and the same 

 for each year. The following remarks hence apply only to species 

 which invariably form a single distinct concentric ring of wood 

 each year. 



1. Determination of the age of standing Ircet. 



The ages of individuals of most of our conifers can, as long aa 

 they are branched down to the ground, be accurately determined 

 by counting the number of annual shoots. The age of other treei 

 can generally be told to within 10-20 years by a forester pcssessed 

 of large local experience. But the most certain way of ascertain- 

 ing the exact age of a tree is to use Pressler's borer, which should 

 be long enough to reach, or all but reach, th centre of the trunk. 



