138 BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTURE. 



the height of the trees, and somewhat shorter distances to the east 

 and west, measuring distances from the outer edge of the crowns. 

 Boot competition, in a degree which, though rarely killing seedlings, 

 noticeably retards their growth, occurs on a patch extending from 

 50 to 75 feet in all directions from the base of tree or outer edge 

 of the group concerned. Beyond these limits the beneficial effects 

 of reduced wind movement equal or exceed the unfavorable influences 

 of shading and soil sapping. It is known, however, that on average 

 sites in this region, western yellow pine seedlings will become estab- 

 lished without the shelter of older trees, and that they make the most 

 rapid growth where all competing vegetation, including herbs and 

 shrubs as well as trees, has been eliminated. The primary object of 

 leaving seed trees after cutting should be seed production. Any 

 surplus of trees above the needs for this purpose is likely to prove a 

 handicap to reproduction. A scattered seed-tree method, in which 

 only from four to five choice seed trees per acre are left, promises 

 to give the best reproduction. Such a practice is not generally 

 desirable at the present time, however, because it sacrifices the grow- 

 ing stock made up of young trees now mostly below 20 inches 

 diameter breast high. From a broad silvicultural standpoint, in 

 which continuous production as well as restocking is sought, the best 

 results can be secured by a selection method of cutting which leaves 

 all healthy blackjacks and a sufficient number of yellow pines to 

 provide a minimum of four seed trees above 20 inches diameter 

 breast high per acre. Under favorable. conditions of soil and rain- 

 fall the number of seed trees might be reduced to three. 



The foregoing obviously applies only to areas on which repro- 

 duction is absent or greatly deficient at the time of cutting. Where 

 appreciable amounts of advance growth occur, fewer seed trees are 

 required, and this reduction is accomplished by decreasing the num- 

 ber of yellow pines. Provision should always be made, however, 

 for seeding up the open spots left by felled trees. Usually this 

 will be taken care of by the blackjacks which are left. It is distinctly 

 desirable to encourage advance growth as much as possible by pro- 

 viding special protection against fire and grazing during a period 

 of about 10 years prior to cutting. This practice not only gives 

 greater assurance of complete stocking, but may be expected to 

 shorten the reproduction period materially. 



BRUSH DISPOSAL. 



The effects of a brush cover vary greatly with the character of 

 herbaceous vegetation, the soil, and the density and stage of dis- 

 integration of the brush. As a general rule, brush associated with 

 exuberant herbaceous vegetation is detrimental to reproduction, but 

 where the herbs are small and sparse or have been eliminated by 



