Wilting Point, estimated by moisture retention at 15-atmospheres of pressure, 

 using standard pressure plate apparatus. 



Percent Sand, determined by hydrometer method. 



Percent Silt, determined by hydrometer method. 



Percent Clay, determined by hydrometer method. 



Available Potassium, determined by flame photometer. 



Percent Organic Matter, measured by Walkely-Black wet digestion chromic acid 

 method (Jackson 1958). 



Total Nitrogen, measured by the micro-Kj eldahl method, using CuSO^ and Na^SO^ 

 digestion mixture. 



Bulk Density, measured by the paraffin coating technique. 



Soil Reaction, or pH, measured with a glass electrode in a saturated paste. 

 Horizon Thickness, measured in the field. 



Water Holding Capacity, estimated by the difference between field capacity 

 and wilting point, and weighted by horizon thickness, rock content, and 

 percent fine material. 



Results and Discussion 



Understory yields ranged from about 100 to 1,200 lbs. /acre (dry weight), and 

 averaged 644 lbs. /acre. 



TIME 



Understory production is expected to be low, both immediately after logging and 

 after canopy closure of the reproducing lodgepole pine stand. Between these two points 

 in time, production should peak. This trend was strongly evident within the 17-year 

 age span of the plots, and was approximated by the sigmoid function, e"^ , where 

 e = 2.718 and k = 0.01667 (age of cut minus age at peak production)^. So the time 

 effect was retained as a component of all models examined. 



Total understory production reached its peak about 11 years after clearcutting . 

 The several vegetal classes, however, performed differently with time (fig. 1). Sedge 

 was the only class that showed no discernible pattern; its mean is shown in figure 1. 

 The regression for grasses was not significant (P> .05), but the data suggest slight 

 peaking at about 13 years. The regressions for forbs and shrubs were significant 

 (P< .05). Forb production peaked at 10 years. Shrub production increased over the 

 entire range of time, but the increase was slower after 11 years than it was pre- 

 viously, and there is a slight but unconfirmed hint of a flattening of production at 

 about 15 or 16 years after clearcutting. These production patterns were determined on 

 sites supporting unthinned lodgepole pine reproduction. Observations in other clearcuts 

 where reproduction had been thinned suggest that thinning may delay the peaking of 

 understory production a few years. If this is true, a grazing potential of perhaps 20 

 years, or more, may be expected on clearcuts where tree regeneration is thinned. 



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