'268 COLLECTION OF STATISTICS. 



natural phenomena, for instance, if the ground has become 

 swampy, temporarily denuded, or covered with moving sand. 



An abnormal condition of the growing wood may be pro- 

 duced by faulty treatment, by injurious external agencies, such 

 as drought, frost, wind, fire, insects, diseases of the trees, etc. 



For the preparation of working plans, only the actually 

 existing, or real, quality of the locality should be taken into 

 account, because the restoration of the normal quality is 

 generally a slow process, if it is at all effected. As regards 

 the growing stock both values are required, because the normal 

 quality represents the real quality of the locality, and the real 

 quality of the growing stock forms the basis for the calculation 

 of the yield which the forest can give. 



On page 150 of Volume I. it has been said that the quality 

 of the locality can be ascertained 



(1) By an assessment according to the several factors of the 



locality ; or 



(2) B.y an assessment according to a crop of trees produced 



on the area in question, or on a similar soil in the 

 vicinity. 



It has also been stated that the first of these two methods, 

 however carefully carried out, is always subject to grave errors, 

 because an examination of the chemical composition and the 

 physical properties of the soil, and a determination of the 

 climate do not indicate the yield capacity of the locality for 

 forestry with any degree of certainty; hence it should be 

 used only as an auxiliary of the second method, or when the 

 latter is not available. 



Thus it will be seen that the determination of the quality 

 of the locality depends practically on an examination of the 

 growing wood which it has produced. In fact, a normal 

 growing stock is the true expression for the real quality of the 

 locality; the same investigation gives both the quality of the 

 locality and of the existing crop. 



For the purpose of obtaining an actual figure, which repre- 



