FOREST SUCCESSION AS A BASIS OF THE SILVICULTURE 

 OF WESTERN YELLOW PINE ^ 



By Robert H. Weidman 

 U. S. Forest Service 



Since the beginning of timber sales on the National Forests 15 years 

 ago, the silvicultural system generally used in western yellow pine has 

 been characterized by a selection method of cutting. At the beginning 

 this method aimed to remove about two-thirds of the virgin stand in 

 the first cutting operation. Inasmuch as the virgin forest was uneven- 

 aged and contained a considerable proportion of mature and decadent 

 trees, the silvicultural objects of the method were to cut over the forest 

 rapidly in order to save the decadent timber, to maintain the uneven- 

 agedness by leaving part of the original stand, and to leave an overwood 

 to start and safeguard reproduction. Another object in reserving part 

 of the stand was to have a basis for periodic cuts on the same ground 

 which would come at intervals of one-third or one-fourth of the rotation. 



Tentatively a rotation of 180 to 200 years was considered, with 

 cutting periods of 40 to 60 years. Whatever the rotation, it was 

 recognized that the first cut would greatly exceed any of the later 

 periodic cuts. In the case of a rotation of 180 years with three cutting 

 periods, it was considered that after the initial cut each periodic cut at 

 intervals of 60 years would amount to approximately one-third of the 

 total rotational yield. And in this case it was assumed that the man- 

 aged forest would become one in which there would, be three more or 

 less distinct age classes differing by 60 years. 



These in general are the ideas which governed the choice of the 

 selection system for western yellow pine. They were based naturally 

 on preliminary studies and observations in the virgin forest. Since 

 then there has been opportunity for thorough study of the results of 

 fifteen years of selection cutting on timber sales, and also of the 

 results of fifty years of cutting on old private areas— cutting which 

 ranged from selection on the older areas to clear cutting on the newer 



^ Paper read before the Society of Airerican Foresters, Berkeley, Calif. 

 August 4-6, 1921. 



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