PETAWAWA EXPERIMENT FOREST STATION. 171 



the development of the crowns and stems. Should the crowns 

 and the stems be normally developed ?w other symbol is added 

 to the figure indicating the crown stratum. If, however, crown or 

 stem is not faultless a letter symbol is added. 



The tree-classes are as follows : — 



{a) Trees with well-developed crowns and stems. 



{p) Trees suppressed on one side, that is, trees which are 



developed only on half of the circumference. 

 (c) Fast-growing trees with large branches (trees of the 



better " wolf type "). 

 {d) Crooked and branchy trees, or trees of otherwise faulty 



growth (trees of the poorer " wolf type "). 

 (g) Trees with compressed crowns, or trees the crowns 



of which have been damaged by the crowns of 



surrounding trees. 

 (_/) Trees damaged by fungi, insects, etc. 

 {g) Dead, broken, or much snowbent trees. 



The grades of thinnings are defined as follows : — 

 Cleaning : Removing dead, dying, or much snowbent trees, 



;>. I.^, 11.^-, III.^, IV.,0. 



"Thinning from under" 



French (eclaircie par le bas). 

 German (neider-durch forstung). 

 Swedish (laggallring). 



1. Light low thinning. 



Removal of dead, dying, snow-damaged, diseased, and 

 suppressed trees, and also the most harmful 

 "wolves," i.e. tree-classes (^), (/), {e) and (^, and 

 all group IV. 



2. Heavy low thinning. 



Removal of tree-classes {b) to {g) of groups I. and II., 

 and all of groups III. and IV. 



3. Very heavy low thinning. 



Removal of tree-classes {b) to {g) of group I. and all 

 groups II., III., and IV. In addition a few of the 

 trees of Class I. may be removed. In larger 

 gaps a few trees belonging to tree-groups II. and 

 III. may be spared. 



