THE MONTANE ZONE 147 



the larger trees of the stand may throw open the land to a con- 

 test for supremacy among the local species. 



There are few parasites to which the lodgepole is seriously 

 subject, and most of these do not destroy the tree, nor apparent- 

 ly retard its production of seed. The most serious enemies are 

 the bark beetles of the genus T) end-rod onus which kill the 

 stands. Among the vegetable parasites Peridermium cerebrum 

 and P. H(irl>'n< ssii and the small mistletoe Rqzoumofskya ameri- 

 cana are the most common, but they are seldom conspicuous. 



Against these more or less favorable traits may be set off 

 three which have a limiting effect upon its distribution. The 

 soil limitations are not a serious handicap to migration. Locally 

 such limitations are effective as in over-watered soils, the lodge- 

 pole requiring well aerated land with a medium amount of 

 available moisture. Some authors hold that the lodgepole shuns, 

 calcareous soils, but that is a matter affecting local rather than 

 general distribution. Otherwise the lodgepole seems indifferent 

 as to the qualities of the soil. The effect of the intolerance of 

 this species, as Avas mentioned above, is seen mainly in the re- 

 tarding of its growth until such time as the shade may be re- 

 moved. The specific light requirements of this species, however, 

 like the edaphic relations, are more important locally than as 

 effecting the whole range of the species. In the third negative 

 element, that of susceptibility to fire, is a factor which must in 

 a far-reaching way affect the prosperity of the species through- 

 out its range and operate to reduce the area over which it may 

 hold sway. 



Thus it will be seen that the positive factors in the make-up 

 of this species far outweigh those which are negative and which 

 would tend to weaken it in its struggle for survival. Such 

 adaptability is reflected in its wide distribution which extends 

 from the peninsula of lower California almost to the Arctic 

 circle and from the Black Hills to the very shores of the Pacific. 



The Engelmann spruce (Picca Engelmannii) is one of the 

 most widely distributed trees of the Rocky Mountain forests. 

 Within the boundaries of Montana it has a wider altitudinal 

 range than any other species. From the crests of the highest 

 ranges it descends to the lowest point, within the State (Troy, 

 1,880 feet) and in Idaho to 1,500 feet. It is a prominent tree 



