SITE INDEX 



100 



90 

 80 



60 



50 

 40 



Figure 13 — Quadratic mean diameter vs. age for Douglas-fir precommercial 

 thinning to 250 trees per aae at 20 years in Inland Northwest forests. 



SITE INDEX 



100 



90 

 80 



70 

 60 



60 



70 80 

 AGE 



90 100 110 120 130 140 150 



Figure 14 — Quadratic mean diameter vs. age for Douglas-fir precommercial 

 thinning to 250 trees per acre at 20 years and commercial thinning from below 

 to 100 trees per acre at 50 years in Inland Northwest forests. 



50 

 40 



17 



