Management of Western Yellozv Pine. 53 



represented by its group. Though occasionally one broad age 

 class, such as saplings or seedlings, may be different over a sec- 

 tion or two, the proportion of the different age classes is on the 

 whole very satisfactory. This distribution into small groups 

 renders the stand analagous to an uneven-aged stand, the group in 

 this case corresponding with the single tree in the uneven-aged 

 stand. 



SilvicuIturaJ Systems. 



The foregoing conditions point to two distinct requirements. 

 First, reproduction must be secured by maintaining the shelter 

 as much as possible ; this shelter can generally be secured, except 

 in the case of large groups, by the immature trees surrounding the 

 group. Second, the silvicultural system over broad areas must 

 be one of periodic cuttings, removing the mature groups in the 

 manner of mature trees under a selection system. 



The system required is, therefore, a form of the selection 

 system which can be called the "group selection system ;" but it 

 will not always be possible to treat each group as a single tree. 

 If a group is very large its removal might make too large an 

 opening; or a group may be surrounded by trees too small to 

 produce sufficient seed, or to provide the necessary shelter against 

 drought and frost. In either case one or two of the most 

 vigorous members of the group may be left ; but, unless the group 

 occurs on a sheltered spot, the trees left must have grown on the 

 side exposed to the wind and therefore be windfirm. They must 

 also possess good crowns. Otherwise, unless the period between 

 cuttings is short, leaving them will be merely a waste of money. 

 Whenever a group containing mature and overmature trees is 

 found, it is generally good policy to cut the entire group unless 

 by so doing reproduction will fail. The groups which are not 

 cut should be left intact except for the removal of the merchant- 

 able over-topped or otherwise defective trees which are perform- 

 ing no useful functions in protecting the group, and will probably 

 not increase in value. The guiding principle in deciding upon 

 the groups to cut, at least for the first cut, should be the length of 

 the felling period or cutting cycle. For example, if the felling 

 period is 40 years all groups which will not live 40 years, or 

 which, at the end of 40 years will be of no greater or of less 

 value than at present, should be cut. 



