10 ELEMENTS OF SYLVICULTURE. 



must begin to make the periodical thinnings. Before 

 the timber has reached the stage of low poles, there 

 is not enough difference between the various stems 

 to enable us easily to distinguish those that are to 

 be the trees of the future ; we run the risk then of 

 making mistakes if we begin to thin so early. 

 Besides, up to this point the effect of the struggle 

 has been distinctly useful, and it has already been 

 pointed out that while making the last cleanings, a 

 sort of partial thinning might be carried out if 

 thought necessary. Under these circumstances it is 

 more prudent to postpone the first periodical 

 thinnings, until the forest has attained the stage of 

 low poles, when the operation can be performed with 

 a certainty of the result; this stage is generally 

 attained towards the age of about forty years. 



In order that the boles may be drawn up to a good 

 height as well as to preserve the crop from accidents 

 resulting from wind, heat, frost, &c., the forest can 

 never be too full. The first thinnings then should be 

 at the most, moderate, and at times there should be 

 no hurry to begin them ; and if the operation is per- 

 formed on quick growing trees which naturally begin 

 to crowd each other comparatively early, it will be 

 sufficient to shorten the interval of time between two 

 successive thinnings. 



To prevent the wind from sweeping through under 

 the forest and thus scattering the dead leaves, no 

 trees must be felled for a certain width along the 

 edges of the forest, except those that are in full 

 decay ; and to make this screen more effective, the 

 low branches on the outside must not be lopped off. 



