CHAP, ix.] Tending of Woods 193 



basal area (i. e. the sum-total of all the stem-superficies at breast- 

 height) is certainly not less than in dense crops raised from 

 seed or by natural regeneration. 



III. A far less percentage of the total number of stems 

 belongs to the dominated and suppressed classes. 



IV. The stimulation of the increment in basal area takes 

 place in accordance with (though it is not necessarily propor- 

 tional to) the degree to which the thinning takes place. 



So long, therefore, as thinning is not carried to such an 

 extent as to prejudice the energy of growth in young crops that 

 have not yet nearly completed their activity, i. e. which have not 

 yet culminated in average annual increment, a free thinning 

 stimulates to the earlier maturity of the crop, and is there- 

 fore decidedly advantageous from a financial point of view. 

 Thinnings are, generally speaking, said to be slight when only 

 dead or dying poles are removed, moderate when all suppressed 

 poles, and also a portion of the dominated poles, are cut out, 

 and heavy when at the same time all the dominated poles are 

 eliminated l . 



It may be noted here that, in tree-forest, a slight thinning 

 removes about 5 % of the basal area of the stems at breast- 

 height in crops of normal density of leaf-canopy, a moderate 

 thinning about 10 %, and a heavy thinning about 15 %. Where 

 it goes beyond this last degree, it becomes in reality a partial 

 clearance, and must be regarded as such. 



The average percentage of basal increment has been given 

 above ; but it must be observed that these figures are subject to 

 modification. For the actual percentage of basal increment is 



1 In the special case referred to on p. 64 the moderate thinning was 

 particularly stated not to include any of the dominated stems, as these 

 were all included in the heavy thinning. But it must be borne carefully in 

 mind that the thinnings were carried out in dense crops of Spruce, which is 

 one of the most shade-bearing kinds of trees. For crops of light- demanding 

 trees, like Oak, Larch, Pines, Ash, Maple, Sycamore, Elm, Birch, Willow, 

 and Poplar, even a moderate thinning would certainly remove a portion of 

 the dominated individuals ; but the extent to which these should be cut 

 out would, in each concrete case, depend on the kind of trees forming the 

 crop, the general vigour of the latter, and the nature of the soil and situation. 



O 



