Site index at a 50-year base age was used rather than at 100 years as in Myers' 

 published example. Stand projection by Myers' method depends on the use of a predicting 

 equation for future d.b.h., which has site index as one of the independent variables. 

 Projections were made for hypothetical stands at higher site index levels than were 

 found on any of the plots that served as the data base for Myers' equation. Neverthe- 

 less, the results obtained appeared entirely reasonable, so projections of stands at 

 the higher site index levels were included in the estimates used to derive the yield 

 capability equation. 



For each site index, a curve of net yield before thinning was plotted over age. 

 It was assumed that the volumes removed in thinnings would be lost to mortality in 

 natural stands. The age of culmination of net cubic volume mean annual increment was 

 estimated by drawing a line from the origin of coordinates tangent to the yield curve. 

 The point of tangency indicated the age of m.a.i. culmination and the net stand yield 

 at that age. Dividing the yield thus obtained by the culmination age gave the m.a.i. 

 at the age of culmination, or the yield capability associated with that site index. 

 Plotting yield capability over site index resulted in the curve shown in figure 6. 

 This curve is described by the equation: 



YC = bg + biS + b2S2, ^ 



where 



YC = yield capability bg = 6.9091271 



S = site index at a 50-year base age b^ = -0.16172109 



b2 = 0.021683019 



WESTERN LARCH 



Site Index 



The following equation for height of western larch in even-aged stands was 

 developed by Arthur L. Roe:-^ 



where 



log H = log S - b^ (1/A - 1/50), 



log H = the common logarithm (to the base 10) of dominant 

 stand height 



log S = the common logarithm of site index at a 50-year 

 base age 



A = total stand age 



bi = 21.036. 



This equation can be easily solved for site index: 



log S = log H + bi (1/A - 1/50) 



S = 0.37956 H • exp (48.4372/A) 



The last equation shown above can be used in computer programs to estimate site index 

 of even-aged stands of western larch. 



■^Principal Silviculturist , Intermountain Forest and Range Experiment Station. 



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