EXPERIMENTAL PROCEDURE 



Objectives of the study were to be achieved by annually measuring the mortality of 

 ponderosa pine trees caused by the pine beetle over a 10-year period following the single 

 initial risk rating of the trees. For this purpose, 35 plots having a combined net 

 timbered area of 553 acres were established between 1948 and 1958 in widely scattered 

 stands of virgin mature ponderosa pine in Montana west of the Continental Divide. 



Financial limitations prevented the sampling of the heterogeneous pine stands in 

 a manner that might statistically test the significance of possible differences in tree 

 mortality rates in each of the several pine forest cover types of the Society of Ameri- 

 can Foresters (1954) or of the pine-dominating vegetation habitat types of Daubenmire 

 and Daubenmire (1968) that might be represented in this region. Neither was it possible 

 to make a sampling to determine possible differences in rates of beetle-caused tree 

 mortality in relation to such stand factors as composition, density, or site indexes. 

 These factors by themselves probably could not be used with sufficient accuracy to pre- 

 dict the amount of tree killing by the pine beetle in specific ponderosa pine stands as 

 reported by Salman and Johnson.^ 



^K. A. Salman and Philip C. Johnson. The forest insect hazard inventory of east- 

 side forest areas, preliminary report on methods and their application. USDA Bur. 

 Entomol. and Plant Quar. , Forest Insect Lab., Berkeley, Calif. Unpub. Rep. 

 Sept. 21, 1937. 



4 



