3. Reciprocal of stand age (1/A). 



4. Reciprocal of western white pine site 

 index (1/WPSI) 



5. Product of western white pine site index 

 and stand age (WPSI-A) 



6. Ratio of western white pine site index to 

 stand age (WPSI/A) 



7. Elevation above sea level (E) 



8. Reciprocal of elevation (1/E) 



9. Aspect: Expressed as the sine (SinAz) 

 or cosine (CosAz) of the average azimuth 

 reading. 



10. Habitat type (HT): A discrete vari- 

 able limited to only three habitat-type condi- 

 tions: Abies /Pachistima, Thuja /Pachistima, 

 arid Thuja- Tsuga/ Pachistima. 



11. Topographic position (TP): A discrete 

 variable having five categories: ridge, upper 

 slope, middle slope, lower slope, and flat or 

 bench. 



12. Western white pine height (WPht): 

 Average height of measured dominant and 

 codominant white pine. 



13. Ratio of western white pine height to 

 stand age (WPht/A) 



Estimating Western White Pine Site index 



Seven of the nine independent variables 

 used in this second series of analyses were 

 the same as in the first; Le., stand age and 

 its reciprocal, elevation and its reciprocal, as- 

 pect, habitat type, and topographic position. 

 The other variables were: 



1. Height of other species: Average height 

 of measured dominant and codominant trees 

 of given species — western larch (WLht), 

 lodgepole pine (LPht), Douglas-fir (DFht), 

 grand fir (GFht) , or western hemlock 

 (WHht). 



2. Ratio of other-species height to stand 

 age (WHht/ A, etc.) 



Values for the two nonquantifiable vari- 

 ables, habitat type and topographic position, 

 were calculated by assigning orthogonal co- 

 efficients to each habitat type and topographic 

 position. The partial regression coefficient 

 obtained from the regression for habitat type 

 and topographic position multiplied by the 

 orthogonal coefficient assigned each habitat 

 type and topographic position gives the value 

 of each. 



RESULTS 



PREDICTING HEIGHTS OF 

 ASSOCIATED SPECIES 



Two equations are presented below for each 

 of the five alternative species. Equation I, 

 based only on stand age and white pine site 

 index, or white pine height alone, provides a 

 simplified means of estimating heights of other 

 species without serious lack of accuracy. 

 Graphs for making specific predictions and a 

 table showing general height comparisons 

 among species are in Appendix A. These can- 

 not be used in a reverse order; that is, white 

 pine site index cannot be predicted from other 



species' height and stand age. The series of 

 equations in the next section are for that 

 purpose. 



Equation II includes all significantly re- 

 lated variables that give increases in accuracy 

 of estimates worthy of consideration. Because 

 of the more lengthy computations and more 

 specific site measurements needed, use of 

 Equation II will generally be limited to situa- 

 tions requiring the best possible estimate for 

 small and quite homogeneous areas. Con- 

 densed tabular values given in Appendix B 

 will facilitate calculations. 



Western Larch Equation I: 



WLht = + 22.6 + 0.79 (WPSI) + 0.74(A) - 1,200 (1/WPSI) - 17 (WPSI/A) 

 For this equation, R 2 = 0.87; Sy = ±8.2 feet. 



3 



