50 LOCALITY AND FOREST VEGETATION. 



quantity of 5,000 cubic feet of wood in the course of 100 

 years, the quality, or annual yield capacity, is represented by 

 ^*^^^=oO cubic feet, in other words, by the mean annual 

 production. 



The applicability of this method depends principally on 

 the following three conditions: — 



(a.) That the existing wood has grown up under normal 

 conditions ; in other words, that no extraordinary dis- 

 turbing events have occurred which affected the health 

 and development of the crop, as, for instance, damage 

 by cattle or deer, insects, fire, theft, removal of litter, 

 faulty treatment, etc. 

 (h.) That the factors of the locality have not undergone 

 any decided change, either for the better or worse, 

 during the production of the crop ; for instance, the 

 stock of humus or the degree of moisture may have 

 been affected by external interference. 

 {('.) That the existing crop is of a sufficient age to make 

 sure that the factors of the locality have found a 

 thorough expression in the same, since a wood may 

 thrive well up to a certain age and then fall oft' con- 

 siderably. 

 Whenever these conditions exist to a fair extent, the 

 method of assessment is the best which is at the forester's 

 disposal ; and in its application he need not restrict him- 

 self to a crop actually growing on the area, but may be 

 guided by one growing on a neighbouring piece of land, 

 provided the general conditions are about the same in both 

 cases. 



A great quantity of data bearing on the j'ield capacity of 

 land under forest has, in the course of time, been collected 

 and brought together in so-called " Yield Tables,'' that is to 

 say, tables which indicate the yield which an acre of land 

 may reasonably be expected to give according to whether it 

 belongs to one or the other quality. 



The details regarding yield tables will be found in 



