214 Studies in Forestry [CHAP. x. 



the more favourable the soil and situation may be to the 

 thriving of the particular species of tree, and the denser or more 

 crowded the wood, so much the more likely is the influence 

 of the thinning or partial clearance to be readily observable. 

 That the extent to which it is perceptible varies in the different 

 genera of our forest trees has been above indicated and really 

 requires no explanation. Thus, for example, Oak, Pine, and 

 Larch, that have been grown in pure forests, in which there is 

 a strong tendency for the trees to thin themselves naturally to 

 such an extent as to make the canopy loose, if not broken, 

 and to allow of each individual stem forming a larger crown 

 than is usual in the case of shade-bearing genera like Beech, 

 Spruce, and Silver Fir, can hardly be expected to derive so 

 much benefit as these latter from any artificial diminution of the 

 number of stems per acre. In many such cases, indeed, this 

 natural thinning, especially when the Oak, Larch, and Pine are 

 approaching the time of maturity of the crop, may have pro- 

 ceeded so far that any further artificial clearance might lead to 

 diminution instead of enhancement of the increment of the 

 remaining stems in consequence of deterioration of the soil, 

 unless underplanting take place at the same time in order to 

 improve, or at any rate protect, its productive capacity. As it 

 is well expressed by Gayer l , the founder of the modern school 

 of scientific sylviculture 



' Whenever the partial clearance is likely to lead to interruption of the 

 canopy of the crop, it should only be carrried out when the productive 

 capacity of the soil is such as promises, in all its essential factors, to 

 supply continuously the increased demands made in consequence of 

 greater energy in the crown of foliage (transpiration and assimilation), 

 i. e. that the soil in question is fertile, or that care may be taken to 

 stimulate the productive capacity of the soil in some suitable way at the 

 proper time. This can only take place through the maintenance of 

 a good layer of humus and the careful retention of soil-moisture, and 

 consequently in many cases only by means of underplanting in order to 

 protect the soil against sun and wind.' 



1 Waldbau, 3rd edit. 1889, p. 571. 



