Figure 2. — The heterogeneity of old-growth ponderosa pine stands in western Montana is 

 illustrated here. Abrupt topography and ocoasional aatastrophio fires^ insect out- 

 breaksj or windstorms are responsible for frequent changes in site conditions over 

 relatively small areas and a resultant lack of continuity in the forest vegetation. 



They also include the Pseudotsuga menziesii/Calamagrostis nibesoens (Douglas-fir/ 

 pinegrass) , Pseudotsuga menziesii/Physooarpus malvaoeus (Douglas- fir/nineb ark) , and the 

 Pseudotsuga menziesii/Symphoricarpos albus (Douglas-fir/snowberry) types in which 

 ponderosa pine is serai. Roe^ is of the opinion that some of the most productive stands 

 of ponderosa pine in western Montana are to be found in some of these Douglas-fir 

 habitat types. 



Composition and Density 



Overstory trees on 12 plots were exclusively ponderosa pine; however, the species 

 probably was climax on no more than half of these plots. In contrast, 27 percent of 

 all overstory trees and 11 percent of their gross board-foot volume on the remaining 23 

 plots were species other than ponderosa pine. 



The most prevalent of these nonpine tree species was Rocky Mountain Douglas-fir, 

 Pseudotsuga menziesii var. glauoa (Beissner) Franco. This was followed by lodgepole 

 pine (Pinus oontorta Douglas) and western larch, {Larix occidentalis Nuttall), which 

 occurred only sparsely on some plots. 



^Arthur L. Roe. Formerly, Research Si Iviculturist , Intermountain Station, Ogden, 

 Utah. Personal communication. 



8 



