LIFE HISTORY OF LODGEPOLE PINE IN ROCKY MOUNTAINS. 23 



nual rings of trees injured or killed by smelter smoke usually show 

 a graduated decrease in size for the last six or eight years. 



With respect to their susceptibility to injury from smelter fumes, 

 the species in the lodgepole region may be grouped as follows, the 

 most easily killed coming first : 



Alpine fir. 

 Douglas fir. 

 Lodgepole pine. 

 Engelmann spruce. 

 Juniper. 

 Limber pine. 



As between Douglas fir and lodgepole pine, the two most impor- 

 tant species in the smoke zone, the former is considerably more sus- 

 ceptible than the latter. Nearly all the lodgepole trees will remain 

 green when practically all the Douglas firs in the same locality have 

 been killed. Susceptibility varies among different individuals of the 

 same species. A few green and flourishing Douglas fir trees will 

 often be found after practically all the other firs in the vicinity have 

 been killed. 



The injury is not the same in. amount at all places equally distant 

 from the smelter, since the smoke is carried by the prevailing wind 

 along channels formed by the topography. Damage decreases both 

 with distance from the smelter and distance from the main channels. 

 In places the smoke seems to eddy in a peculiar manner, killing trees 

 in isolated groups. The greatest damage, of course, is close to the 

 smelter, but at places 9 miles distant most of the lodgepole is now 

 dead and the remainder seriously injured. Slight damage at a dis- 

 tance of 30 miles has been observed. 



WINDFALL, SUN SCALD, ETC. 



Lodgepole pine is generally regarded as being decidedly susceptible 

 to windfall. While to a certain extent this is true, there is a tend- 

 ency to exaggerate the danger. The extent of the development of 

 the tree's root system, as in the case of any other species, varies with 

 the soil conditions and the density of the stand. On deep, fresh soil 

 trees in moderately open stands develop good root systems, while on 

 very shallow or very moist soils the root system is correspndingly 

 shallow and the tree less wind firm. With the same soil conditions, 

 the development of the root system varies inversely with the density 

 of the stand, so that the denser the stand the less windfirm are the 

 individual trees. Experience shows that heavy thinnings in dense 

 stands are very likely to result in serious windfall unless the situa- 

 tion is well protected. For this reason the leaving of seed trees, 

 either alone or in small groups, seldom works satisfactorily. On 

 the more exposed situations, with shallow or wet soil, even unthinned 



