DIAMETER INCREMENT. ^l 



with Pressler's increment borer. The number of years, for 

 which it can be ascertained, depends on the length of the 

 cyHnder, which can be extracted, and on the rate of growth. 

 As most trees grow irregularly, it is necessary to ascertain the 

 increment at opposite sides, or at four sides, and to take the 

 mean. These investigations rest on the assumption, that the 

 concentric rings are distinguishable, and that each ring repre- 

 sents one year's growth. 



The increment can be ascertained with much greater accuracy 

 by felling a tree and measuring the breadth of the desired 

 number of rings on the section, the latter being laid at right 

 angles to the axis of the stem. The measurements are made 

 with a scale subdivided to a sufficient degree. This is either 

 laid on the section and the breadths read oft", or the latter are 

 taken off with a pair of compasses, and the dimensions then 

 taken from the scale. In either case, care must be taken to 

 obtain averages by measuring along two, four, or more radii, 

 arranged at equal distances over the section, and then taking 

 the mean of the several readings. 



In the case of standing trees, the increment can only be 

 ascertained for a limited number of years. If a tree is felled, 

 the increment can be ascertained for the several periods of its 

 life, sa}', for every live, ten, or more years. The result can be 

 graphically represented and a mean curve of increment con- 

 structed, from which the increment for any desired intervals 

 can easily be determined. By repeating the above operation 

 at successive heights from the ground, the increment can be 

 ascertained in the several parts of the stem. 



h. Diameter Increment of the Future. 



This is estimated from the increment of the immediately 

 preceding period, taking into consideration, how far the 

 future diameter increment may be affected by the method 

 of treatment, more especially the proposed degree of thin- 

 ning ; the stronger the latter, the greater is the increment 

 likely to be. 



F.M G 



