296 



The Thinning of Woods. 



fere with the more rapid development of the dominant 

 stems from among which the future mature crop must be 

 formed by means of the survival of the fittest. The 

 prolongation of the struggle for existence in the case of the 

 weaker stems directly prejudices the development of the 

 stems of stronger growth, by leading to a dissipation ot 

 vegetative energy which can, under the guiding hand of the 

 forester, be utilised for the more vigorous increment of the 

 stems of forward growth. To regulate the number of stems 

 in any wood still in vigorous growth, or capable of being 

 thereb3^ stimulated into enhanced energy, is therefore the 

 object of thinning. 



The natural tendency of forests to thin themselves depends 

 on the kind of tree and the quality of the soil. Light- 

 demanding trees, like Oak, Ash, Scots Pine, or Larch, thin 

 themselves sooner and to a greater extent than Alder, Maple, 

 Sycamore, or Austrian Pine ; and these again thin themselves 

 before the suppression of weakly stems takes place among 

 shade-bearing kinds like Beech, Spruce, or Silver-Fir. 

 Again the processes of domination, suppression, and final 

 elimination of unnecessary stems takes place more rapidly on 

 poor than on good soils. Observations made in the Harz 

 Mountains in Central Germany with regard to Spruce growing 

 in woods naturally regenerated, or raised from thick sowings, 

 she wed the following to be the average number of stems and 

 the individual growing-space per stem at different ages : — 



Age in Years. 



Stems per Acre. 



Average Growing-space 

 in Square Feet. 



20 



9,265 



4-6 



40 



1,249 



34-5 



60 



604 



70-0 



80 



388 



IH'O 



100 



282 



152-0 



120 



238 



182-0 



These statistics show that on the Continent such timber 

 crops are much denser than British landowners have been in 

 the habit of growing them. The out-turn in Spruce woods 

 of normal density at any given age varies, according to the 

 quality of the soil, from a total of about 5,000 to 11,000, and 

 even 12,000, cubic feet of clean, well-grown timber per acre. 



