SAMPLE PLOT INVESTIGATIONS IN SCOTLAND. 1 69 



a wood is selected, and two or more sample plots are laid out 

 side by side. The size of the sample plots is from "25 to "5 acre. 

 Round each sample plot an area is demarcated which is thinned 

 and otherwise treated as the sample plot. The object of this 

 surrounding area is to provide sample trees, from time to time, 

 to complete the growth statistics without disturbing the sample 

 plot. On the average each sample plot with its surround 

 extends to about i acre. Within the sample plot each tree 

 is given a number, which is stencilled on the tree with white 

 paint. The next step is to describe each tree on a definite 

 scheme, recording its degree of dominance in the crop, its 

 crown and stem form The object of this classification is to 

 give a basis on which to make the thinnings and a means of 

 recording accurately what is done. 



With regard to the thinning methods which are being 

 investigated, as foresters know, there are two main classes, 

 namely : — 



(i) Thinnings from under. 



(French — tldaircie par le bas). 



(2) Thinnings from above. 



(French — Eclaircie par le haui). 

 In thinnings from under, the thinnings are directed from 

 the lowest canopy level upwards, i.e. all suppressed trees not 

 required for soil cover are removed, together with a greater 

 or less number of defective trees in the upper canopies, 

 depending on the heaviness of the thinning. It is generally 

 a light thinning of this class, namely, a Grade "B" thinning 

 (following the nomenclature of the Association of German 

 Forest Experimental Stations) which is used as a control on the 

 groups of experimental thinning plots. In this grade only such 

 types of trees as dead, dying, suppressed, and whips are removed. 

 This grade is frequently contrasted with a Grade " C " thinning, 

 a heavy thinning from under which gradually removes all 

 suppressed, backward, and defective trees, large and small, 

 which can be removed, without permanently breaking the 

 canopy or endangering the development of the crop. 



In thinnings from above the practice is to leave the suppressed 

 and backward trees, except the dead, dying, and diseased, and 

 to make the thinning in the defective dominants with a view 

 to aiding the development of the best trees. Leaving the 

 smaller trees enables this to be done without unduly exposing 



VOL. XXXVI. PART II. M 



