THE MONTANE ZONE 155 



in the northern Rockies, where it seems to reach its best develop- 

 ment at 6,000 feet or above. 



The positive qualities of the whitebark pine are few; it 

 produces seed liberally, endures a wide range of temperature 

 and seems adapted to rocky situations and meager soil. On the 

 other hand it is limited by the lack of facility in seed dispersal, 

 the seeds being heavy and large, which also renders them at- 

 tractive to squirrels and other animals. The tree is intolerant, 

 it thrives only in moist soil and having thin bark is readily in- 

 jured by fires. 



The seeding habits of this species are somewhat peculiar. 

 Wind can have little influence on seed dispersal in a case where 

 the seeds are devoid of wings or structures which serve a sim- 

 ilar purpose. The cones do not open to discharge their seeds 

 but disintegrate at the core. Cones falling to the ground if 

 spared by animals, often give rise to trees in groups, Such trees 

 may differ much in size, but an examination of the stem section 

 will usually reveal the fact that they are of the same age. As 

 one tree of the group gains the ascendancy it comes ultimately 

 to stand alone. As the seeds of this species are wingless, their 

 distribution is not dependent upon the wind, and other agencies 

 must therefore account for their dispersal, in which squirrels 

 and other seed-eating animals doubtless have a large share. The 

 rare appearance of seedlings at relatively low altitudes, and 

 where it is practically certain there is not a seed tree within 

 miles, suggests the influence of birds. Among birds it is prob- 

 able that the chief agency is the Clark Nut-cracker or Clark 

 Crow (Nucifraga columbiana ) . Skinner (58) states that it pre- 

 fers pine seeds, sometimes tearing cones to pieces while yet at- 

 tached to the branch. More often the cone is detached and car- 

 ried away to a strong limb where it is held with one foot while 

 the bird strikes strong downward blows at it with its pickaxe bill. 



In its temperature relations the whitebark pine shows a ca- 

 pacity to endure a wide seasonal range said to be from 60 to 100 

 degrees, but for the most part it is restricted to cooler levels 

 of elevation, seldom below 6,000 feet in Montana, though the 

 writer has sometimes found isolated individuals at 3,500 feet 

 in western Montana. It is found at about 6,000 feet in Glacier 

 Park and about the same in the Swan Range, from 6,000 to 



