170 TRANSACTIONS OF ROYAL SCOTTISH AKBORICULTURAL SOCIETY. 



the forest floor. In this class of thinning, Grade " D " is 

 being investigated. This is a light thinning of this kind, 

 but from the point of view of what is removed, is a heavy 

 thinning. This grade may be of value for a species such 

 as Douglas fir, a considerable proportion of whose dominants 

 are often of bad stem form. 



In order that the development of the trees may be recorded, 

 complete measurements are made. Each tree is girthed with a 

 steel tape at a marked point (4 ft. 3 ins. from the ground). 

 Eight to ten sample trees are felled in the area demarcated 

 round the sample plot. These trees are measured in lo-feet 

 sections over and under bark. The total height, crown and 

 other measurements are made also. For the five largest sample 

 trees, after cross-cutting, ring-counts are made at different 

 heights to enable an age-height graph to be constructed. This 

 shows the trend of height-growth from the formation of the 

 wood. The thinnings are measured separately. From these 

 measurements the following growth-statistics are calculated : — 

 number of trees per acre, height of tallest trees and mean- 

 height, form-factor (an under-bark true volume form-factor), 

 girth at 4 ft. 3 ins., basal area per acre at 4 ft. 3 ins,, true 

 volume under bark per acre and bark per cent. A similar set 

 of statistics is obtained for the thinnings. The successive 

 measurements will give the periodic and periodic mean annual 

 increments for both basal area and volume. The volume 

 determinations are made by a graphical form-factor method 

 devised by Schwappach, and in use in India for sample plot 

 investigations. 



In addition to the measurements a study and record is made 

 of all the factors of locality, such as soil, vegetation, exposure, 

 climate, etc., and all available knowledge regarding the previous 

 history of the crop is noted. 



The plan is to remeasure, study, and, if necessary, thin the 

 sample plots every five years. The final assessment of the 

 different thinning methods will be made on all the data collected 

 during the whole period of the investigation, including a study 

 of the timber produced. 



In addition to the main investigation into methods of thinning 

 by groups of contiguous plots, single sample plots of the newer 

 species are being established to supplement our knowledge 

 regarding their growth. 



