1 62 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



According to investigations carried out by Herr Philipp, a 

 silver fir, in order to belong to the first class, must have the 

 following proportions (diameter measured at breast-height) : — 



" A minimum diameter of 55 centimetres if 30 metres high. 

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Stems which have reached the prescribed diameter for a given 

 height would after that only have a quantity increment, whereas 

 those under that diameter of the same height would have not 

 only a quantity increment but a quality increment as well, and 

 in such cases as these the discriminating powers of the skilful 

 forester in regard to thinning might be exercised with the most 

 valuable results. Though apparently simple, a " selection " 

 system, in order to obtain the best financial results, really 

 requires more skill on the part of the forester than any other. 



Theoretically no part of the forest is ever at rest — a system of 

 felling and regenerating is going on continually all over the 

 area, but in practice the forest is worked by compartments. 

 Healthy growing trees are considered mature when they attain 

 to the dimensions of Class I. stems. This financial maturity is 

 reached between the age of 100 and 140 years, the general 

 average rotation being 120 years. 



In order to maintain proper forest conditions and keep up the 

 irregular character of the crops, a normal growing stock has to 

 be maintained, corresponding to the normal mean annual incre- 

 ment, with age-classes also normally distributed. Working-plans 

 are renewed every ten years, when the volume of timber in each 

 compartment of forest is measured in diameter classes, the 

 amount of sound timber being separately reckoned from what is 

 faulty. 



Besides the regular cuttings, confined to prescribed compart- 

 ments, accidental fellings — the result of snow-break, windfall, 

 etc.— are continually taking place under good management, and 

 these accidental fellings amount to as much as from 20 to 30 

 per cent, of the whole. Where there is no good system of roads, 

 much of the accidental fall is not fully utilised. 



Beech is less encouraged in the silver fir forests than formerly. 

 Its chief use is for fuel, but as the silver fir is a sufficiently good 

 soil-protector, the beech is less required than in woods of oak 



