THE SELECTION SYSTEM 53 



The Diameter Limit 



While theoretically one aims to select trees for cutting 

 on a basis of age, in actual practise the decision whether 

 a tree is to be cut or left standing for a later cut depends 

 more on its size, condition, and capacity for growth than 

 on its age. For this reason it is usually customary to 

 restrict the cut on a basis of size rather than of age. The 

 size set as a minimum for cutting is called the diameter 

 limit. 



The purpose of a diameter limit is to aid in restrict- 

 ing the cutting to those trees whose growth no longer 

 represents a return satisfactory to the owner. The trees 

 which are thrifty and growing rapidly are left standing, 

 regardless of their age, as a basis for a later cut. 



It is, of course, impossible to investigate the growth 

 of each tree before cutting. It is, therefore, customary 

 to determine in advance of cutting the average diameter 

 at which trees cease to yield a satisfactory growth. Un- 

 less there are some special silvicultural reasons for modi- 

 fying it, this limit is used in planning the work of 

 cutting, and as a guide and check in selecting the trees. 



When possible, the diameter limit of satisfactory 

 growth is determined by a thorough local investigation. 

 Such a study will show the rate of growth of stands cut to 

 a number of different diameter limits, and will enable 

 the owner to fix upon that limit which will result in a 

 return most satisfactory to him. In making the study 

 the forest is first analyzed, to determine the average num- 



