vi] METHODS OF TREATMENT 47 



Under these local conditions of growth, this table gives us 

 the percentage proportion of each group of size-classes, if the 

 succession is complete and regular, and occupies equal areas. 



It would not be very safe of course to take these figures for 

 the very smallest size-class, which is the least easy and the least 

 important to estimate, but we get some idea at any rate of the 

 proper proportions that ought to exist, on every acre, of the 

 larger and middle-sized classes. We might perfectly well work 

 this out in greater detail by taking fifty or any other number of 

 sizes, instead of making only five groups. 



Another good method of ascertaining whether the relative 

 proportions of the different age-classes are correct, is to plot a 

 curve to represent these proportions after each enumeration. 

 It is possible to plot a normal curve of this kind, and any 

 deviation from the normal will at once be clearly indicated by 

 comparison with it. This will show which age-classes are in 

 excess, and which are deficient. 



It is to be noted that under the Selection method the regenera- 

 tion of the forest does not primarily depend on the fellings as 

 it does in the even-aged forest. The principal- fellings in the 

 Selection method may often to some extent result in some local 

 regeneration, and still more may they assist the development 

 of young growth waiting to be uncovered, but they are not 

 entirely responsible for the general regeneration of the forest, 

 which should be taking place naturally and automatically over 

 the whole forest all the time. 



When the group method is applied to forests of mixed ages 

 worked by the Selection method, mature trees are extracted by 

 groups instead of by single stems, and these groups are subse- 

 quently expanded by later fellings, as the young growth in and 

 around them develops. In this case the fellings bear the full 

 character of regeneration fellings, although the natural regenera- 

 tion is not confined to the areas actually included in these group 

 fellings. 



Under the Selection method, tending operations are generally 

 of less importance than they are in even-aged crops. Unless, 

 however, the felling-cycle is a very short one, of five or ten years, 

 it will be necessary to carry out a cleaning or improvement 



