On the basis of the 553 acres of the 35 plots, Risk 3 and Risk 4 trees together 

 averaged 3.2 trees and 3,342 board feet per acre. The mean per-acre volume of these 

 high risk trees varied in each of the 35 plot stands, but it was less than 2,000 board 

 feet in only eight of these stands (table 5). 



Risk 3 and Risk 4 trees together represented 14.9 percent of the 11,946 mature 

 ponderosa pine trees measured during the study; their total volume constituted 19.9 

 percent of all measured pine trees. These percentages, too, varied among the 35 

 plot stands (fig. 5). 



40| 



(0 30 

 liJ 



UJ 



PLOTS 



Figure 3. — Variation in the percentage of pooled Risk 3 and Risk 4 trees in 

 overstory stands of mature ponderosa pine on 35 plots in western 

 Montana. The horizontal position of the plots is not necessarily 

 the same in the upper and lower histograms. 



17 



