24 THE FACTORS OF FOREST PRODUCTION. 



conditions, such as exposure to, or protection against, cold or 

 strong air currents, the aspect and slope of the locality. Generally, 

 trees do best in the centre of their natural distribution, which 

 may be called their " optimum." Towards the limits of the dis- 

 tribution area, whether it is approached by increasing latitude or 

 rising in the hiUs, growth decreases until it ceases. Even too high 

 a temperature, though it may stimulate production, is not 

 favourable in the long run. 



2. The Capital of Forestry. 



The capital of forestry consists of : (1) permanent works, such 

 as buildings, means of transport, as permanent roads, forest 

 railways, timber slides, wire tramways ; (2) the soil ; and (3) the 

 growing stock. The part mentioned under (1) represents in some 

 cases a considerable capital, but in the majority of cases it is of 

 comparatively small amount if compared with the value of the 

 soil and growing stock. The latter two represent the main part 

 of the forest capital. The soil is called the " fixed," and the 

 growing stock the " shifting," or " movable," capital of forestry. 



In the case of a single wood of even, or approximately even, 

 age, the capital represented by the growing stock is small while 

 the wood is young, but it increases with advancing age. It 

 disappears when the wood is cut over, and it is built up again by 

 the accumulation of successive annual increments produced by a 

 new crop. When the forest consists of a number of woods and the 

 management aims at the realisation of a sustained and approxi- 

 mately equal annual return, the growing stock must consist of a 

 series of age gradations, or age classes, of which the oldest is cut 

 annually or within a limited number of years and replaced by new 

 increment. Hence, there is the same amount of growing stock 

 permanently in the forest called the " normal growing stock." 



The proportion between the value of the soil and that of the 

 normal growing stock depends on the .species, the method of 

 treatment, the length of the rotation and the yield capacity of 

 the locality. In coppice woods the fixed may be greater than 

 the movable capital, but in high forest, where the object is to 

 produce timber of some size, the growing stock is usually of 

 considerably greater value than that of the soil, and under a 

 high rotation the ])roportion between the two may be as much 



