174 Forestry Quarterly 



Sun scald sometimes destroys the cambium on the sunny sides 

 of isolated individuals suddenly exposed to full sunlight; this 

 seriously injuries or even kills the tree. 



Frost cracks are occasionally a serious source of injury to old 

 timber. 



Snowbreak sometimes brings about a beneficial thinning in 

 over-dense pole stands, but injures poles left in selection cuttings. 



Lodgepole characteristically occurs in pure, or nearly pure, 

 stands through the greater part of its altitudinal range. Toward 

 the lower limit of the zone, where the minimum necessary amount 

 of moisture is approached, it occurs in mixture with and finally 

 gives way to Douglas fir. Toward the upper limit of the zone, 

 owing mainly to the decreasing average temperature. Engelmann 

 spruce and Alpine fir tend to replace the Lodgepole. All three 

 of these species are more tolerant than the Lodgepole and would 

 doubtless long ago have replaced it over much, if not all, of its 

 present range if it were not for the frequent occurrence of fires 

 in the past. It is, however, a very ancient species, as has been 

 shown by the study of the palaeobotany of Yellowstone Park, 

 where it appears to have occurred in the Tertiary Age (Pinus 

 premurrayana) , as a contemporary of species of Sequoia, Juglans, 

 Hicoria, Fagus, Castanea, Ficus, Magnolia, etc., none of which are 

 now found in the Park. 



In Lodgepole stands the ground cover usually consists of pine 

 grass, weeds, huckleberry, etc., affording fairly good range. 

 Usually very little duff accumulates. The stands, typically even- 

 aged as the result of fire, are usually found to be well distributed 

 among the various age classes, when a good-sized area, such as a 

 National Forest, is considered, thus presenting a splendid condi- 

 tion for the introduction of regulated management. Fire usually 

 renews the stand before it reaches an age of more than 160 years, 

 although stands having an age of 200 years or more are found in 

 places over areas several thousand acres in extent. The oldest 

 stand of which there is record is one on the Beaverhead National 

 Forest in Montana, which is now about 450 years old. Many- 

 aged stands sometimes occur as the result of having started as 

 very wide spaced reproduction on double bums, the blanks of 

 which have gradually reproduced. 



The yield of a stand of a given species depends, of course, upon 



