Becaiise of our concern with mature trees, the study plot stands were selected 

 primarily on the basis of the descriptive qualities of their overstories. Reasonable 

 homogeneity among plot stands was achieved by adopting minimal criteria for selecting 

 them. They contained at least 10,000 gross board feet of ponderosa pine per acre in 

 trees 11.1 inches in diameter breast height (d.b.h.) or larger. At least 50 percent of 

 these trees were in the mature or overmature age classes of the Ponderosa Pine Tree Class- 

 ification (Keen 1943). In effect, these were virgin, commercially operable pine stands. 



All trees on the plots over 11.1 inches d.b.h. were measured and their gross 

 board-foot volumes (Scribner scale) were later computed. Ponderosa pine trees on the 

 plots were serially numbered, tagged for identification, risk rated, and classified by 

 age and long-term vigor using the Ponderosa Pine Tree Classification. This provided 

 a basis for the study of nearly 12,000 sawlog-size ponderosa pine trees containing a 

 total gross volume of 9.3 million board feet. For phases of the study concerned only 

 with the accumulated mortality of risk rated trees, this basis was reduced to 6,800 

 pine trees having a total volume of 4.8 million board feet on 270 acres' because of 

 experimental sanitation-salvage or random selection cuttings made on 12 of the plots 

 during 1957 and 1958. 



Stands on the plots were examined annually to locate and record the deaths of 

 ponderosa pine trees caused by the western pine beetle or the mountain pine beetle dur- 

 ing the previous year. To isolate and identify this source of tree killing, we recorded 

 the deaths of trees caused by quick-acting lethal agents--windstorms , lightning, fire-- 

 or from other cambium- feeding insects'^ (Johnson 1966). 



No fire-killed pine trees were reported during the study. Pine trees obviously 

 killed by lightning or uprooted or lethally damaged by windstorms were recorded by their 

 serial numbers and previously obtained dimensions and descriptions. Pine trees 

 apparently killed from other causes were felled and their boles were systematically 

 examined to detect and record the presence and distribution of attacks, if any, of the 

 two pine beetles or of other tree-killing, cambium- feeding insects (Johnson 1967). 

 Knowledge of the biology and phenology of the various insects involved was a requisite 

 of the bole examinations. It was possible to identify the insect or insects that were 

 infesting each tree bole and to determine which of them was probably responsible for 

 the immediate death of the tree from (1) the observed progress of the construction of 

 parent beetle egg galleries and larval mines, and (2) the metamorphic stages of the in- 

 sects present. 



The risk rating's concern with tree vigor suggested an investigation of soils on 

 the study plots to determine whether a relationship existed between the presence of 

 certain soil characteristics and the abundance of high risk trees in the plot stands. 

 At the request of the Intermountain Station, soils on 15 of the risk rating plots were 

 classified by the Soils Management Branch, Division of Soils and Watershed Management 

 Branch, Northern Region, USDA Forest Service. A brief description of the methods used 

 is quoted here from the report^ of the completed classification: 



The soils on 15 research plots in western Montana were examined in the 

 field. Preliminary identification of the soils was made. The relative 

 depth and texture of the soils were particularly noted because they are 



^Notably, the pine engraver, Ips pini Say, or the California flatheaded borer, 

 Metanophita aalifovnioa Van Dyke (Coleoptera: Buprestidae) . 



^R. C. McConnell. Correlation between soils and bark beetle susceptibility 

 classes for ponderosa pine stands, western Montana research plots. Unpub. Rep., USDA 

 Forest Serv. , Northern Region, Missoula, Montana. 6 p. 1966. 



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