The damage to regeneration by sheep and cattle is due mostly to trampling. In an 

 early study (Sparhawk 1918) mortality from grazing animals varied from 0.7 percent in 

 the 3-1/2- to 4-1/2-foot high seedling class to 59.2 percent in seedlings less than a 

 year old. Fortunately, damage from grazing stock can be avoided and their exclusion 

 should be part of the management plan until the average tree is 4-1/2 feet high. 



Competition. --No other mortality cause is as relentless as the contest among 

 individuals for light, moisture, or nutrients. Moisture is scarce in the growing 

 season on typical ponderosa pine sites, and therefore the more complete and the more 

 enduring the reduction of competition, the greater the survival of seedlings. After 

 the seedlings become established, competition develops between trees of the new stand. 

 This can be controlled by management through regulation of the stocking density of the 

 stand. Stocking density affects the growth of the trees as well as their survival, 

 health, and vigor. Desirable stocking for different management 'goals is determined by 

 complex biological and economic considerations. Accumulated evidence indicates a 

 rather wide range of densities within which total stand volume growth is nearly 

 constant. Thus, forest managers have considerable latitude in managing individual 

 stands according to their needs. 



Some degree of stocking control is needed in ponderosa pine stands of the northern 

 Rockies, even though the actual stocking favored may vary. Control of the growing 

 stock through management will reduce the volume of wood lost through competition in 

 overstocked stands and advance the date when trees reach merchantable size. 



36 



