Figure 2. — Because vegetation was not completely eliminated, competition has reinvaded 

 this plot 1 year after stripping by bulldozer. 



Site Preparation and Treatment 



When regeneration, either natural or artificial, is to be established, some kind 

 of site preparation is usually necessary, to remove competition and expose mineral soil. 

 Evaporation is slower from mineral soil than from forest duff. The better moisture 

 relations of mineral soil make it a better medium for pine seed germination and seed- 

 ling survival (Roe and Squillace 1950) . 



Throughout the growing season, plants of all kinds draw moisture from varying 

 depths of the soil. The wilting point is often exceeded at depths down to 2 feet in 

 vegetated soils. In availability of moisture, the first year is the most critical 

 period for the tree seedling. Upper soil layers dry quickly and first-year roots may 

 not grow fast enough to reach lower moisture supplies. Although the vertical penetra- 

 tion of roots of 1-year natural ponderosa pine seedlings is known in extreme cases to 

 reach 51 inches, they are found more commonly at the 16- to 20-inch depth (Curtis and 

 Lynch 1965) . The removal of competing vegetation makes moisture available for tree 

 seedlings and increases the survival of natural regeneration and outplanted nursery 

 stock (Foiles and Curtis 1965b; Curtis and Coonrod 1961). 



On areas needing regeneration the competing vegetation may consist of grasses, 

 sedges, forbs, and shrubs. Forest soils also contain seeds which germinate when the 

 site has been disturbed (Curtis 1952). As many as 948,736 viable seeds per acre of 

 forbs, grasses, sedges, and shrubs have been recovered from the topsoil in the 

 ponderosa pine type of central Idaho (Krygier 1955) . When the vegetation on a site 

 is removed and the top few inches of soil are pushed aside there is less competition 

 than if only the existing vegetation is removed. The thoroughness with which live 

 vegetation and seed in the mineral soil are eliminated from a site will determine the 

 rate of reinvasion from seed and from sprouting root systems (fig. 2) . Removing part 



6 



