52 METHODS OF TREATMENT [CH. 



of even-aged crops over the whole area with which we are 

 dealing, aged from one year old up to the age of exploitability, 

 which is probably between 100 and 200 years old, it would seem 

 at first sight necessary to spend an equal number of years to 

 achieve this result. In practice this conversion may be com- 

 pleted in a considerably shorter period, because absolute 

 uniformity is not attempted, and therefore a great deal of the 

 younger growth already on the ground is left there to be in- 

 corporated in the new crop, although it will be of course really 

 a good many years older. 



During the process of conversion then, what we understand 

 by an even-aged crop is not a crop composed entirely of trees 

 of the same, or even approximately the same, age, but it is a 

 crop sufficiently even-aged to be regenerated, when its time 

 comes, in one set of regeneration fellings. Exact uniformity 

 would entail also a great waste of production, and the sacrifice 

 of a large quantity of immature stock, so we shall take a middle 

 course and be satisfied for this first rotation if each part of the 

 crop is mainly composed of trees within, say, about thirty years 

 of the theoretical age. 



The procedure then will be to examine carefully each com- 

 partment and sub-compartment, and to make enumerations over 

 representative areas either by linear surveys, or by sample 

 plots to ascertain the predominant proportion of size-class in 

 each part of the crop, and we shall prepare a table to collate size 

 with age. Then, after determining the rotation to be adopted 

 under the new method of treatment, and having settled on a 

 suitable period within which to complete the regeneration of any 

 block, we shall form a general framework of the plan for con- 

 version, allotting each unit of area compartments and sub- 

 compartments to its appropriate period in this general scheme. 



In periodic Block I, will be placed those parts of the crop in 

 which regeneration is already abundant, and trees of the largest 

 class numerous. In Block II, crops containing most class II 

 trees, or class I and III trees, if class II trees are deficient; and 

 so on. 



In the last block will be placed the poorest and least satis- 

 factory parts of the crop, which require to be nursed up and 



