442 ESTIMATION OF INCREMENT 



is well to make two borings at right angles to each other 

 and to take the average between them. The boring should 

 always be done in a horizontal plane and directed towards the 

 centre of the tree. If the rings be not distinct, an alcoholic 

 solution of aniline will usually make them more visible. 



Now, since the average width of the annual ring is the 

 average annual radial increase, it follows that the average 

 annual increase of diameter is twice the width of this ring. 



Hence, it is easy to estimate the future diameter 5 or 10 

 years hence ; and, in practice, it is not advisable to exceed 

 the latter number of years. 



For example, supposing a tree be 10 inches diameter 

 under bark at breast high, and that it be 45 feet high (to 

 the top), and that the form factor for saleable timber be 0-4, 

 and that it be required to find the increment that will take 

 place in the next 8 years. 



It is reckoned that the tree will be 9 feet higher in 8 years' 

 time, and, as found with a Pressler borer, the last 6 years' 

 growth show i inch radius. 



Therefore, in 8 years' time the diameter will be increased 

 by 2-66 inches. Hence, it will be 1 2-66 inches ; and the form 

 factor may be taken as the same as previously. 



Hence, by the formula given, the increment will be, in 

 feet : 



/(i2.66)^ x 54 x Afljogxir 



V 144x4 / V 144X4 



_ /i6o-27 x 22 x 54 x 4 \ /ioox 22 X45 x4\ 

 V 144x4x7x10 / ~ \ 144x4x7x10 / 



= 1 8-8 -9-8. 

 = 9 cub. ft. 



And the percentage increment, if obtained by a formula 

 already explained, will be : 



. __ 200 18-8-9-8 



n 18-8+9-8 



. , . 200 9 



~8~ < 2^6 



= 28^6 

 = 7-86 per cent. 



