THE SUMMITS 159 



its liberal seed production, its capacity for resisting a vigorous 

 climate, where the temperature falls to -60 degrees, high winds, 

 adaptability to various soils but not strict in its demands upon 

 soil moisture. It is thin barked and could easily be injured by 

 fire, but in the open stands where it usiially occurs there is less 

 danger from this menace than is usual with other species. It 

 seems not to be especially susceptible to disC'ase. On the other 

 hand its disadvantages in the matter of seeding, the limitations 

 in the facilities for dispersal, the size of the seeds and the eager- 

 ness with which they are sought by animals, and its intolerance 

 of shade militate against its dominance in the range which it 

 occupies. 



The limber pine has an extensive total range from Alberta, 

 southward through the Rocky ^fountains to New Mexico and 

 westward to California. In the Belt Mountains it comprises 

 about 8% of the forest species and' about 2% in the Absaroka 

 Range. It mingles more or less with lodgepole pine at the upper 

 limits of distribution of that species and in the higher sub-alpine 

 zone is found with spruce, fir, and whitebark pine. 



The Summits. 



The sub-alpine zone of the ilontana Rockies, as above 

 defined, represents the Iludsonian zone of Merriam and is 

 with reference to all parts of its vegetation, a zone of sur- 

 passing interest. Its tree forms are few, it has a limited num- 

 ber of shrubby species and a considerable number of herbaceous 

 perennials. The trees are Tunis albicaulis, P. flexilis, Larix 

 L/jciUi, Picea Engelmannii, Tmga Mericnsiana, Abies lasiocarpa, 

 and Juniperus sco'pulorum. In shrubby form Juniperus com- 

 munis also occurs in abundance. All of these except Lyall's 

 larch and the black hemlock have a distribution extending across 

 the State from north to south, and all except these two and the 

 limber pine are fovmd on both sides of the Continental Divide. 

 Two of them, Picea Engelmannii and Juniperus scopulomm, 

 have a wide range of altitude, from the crest of the divide at 

 6,000 feet or more down to the lowest point in Montana. Larix 

 Lyallii belongs consistently to the high altitudes. 



The aspect of the sub-alpine zone is not that of a continuous 



