THE MONTANE ZONE 139 



So far as observed, none of the plants seen first on the slope at 

 4,000 feet or above fail to extend to the sub-alpine /one, some in 

 sheltered canyons and ravines and others on open and exposed 

 slopes. Among' such may be mentioned: 



Xeroph,yllum Doi!</lxii M< nzi<si glafoella 



Veratrum calif oni ictun Pcbchystima Myr&init'es 



membranaceum 



Referring again to the trees of the Montane or middle 

 mountain belt, the first of the species from the standpoint of 

 its numbers, its characteristics and the breadth of its distribution 

 is the lodgepole pine (P. contorta). 



The lodgepole forests have been studied by Clements (12) 

 in Colorado and by Mason (39) in Montana and elsewhere. From 

 various standpoints they are of great interest and importance. 

 They represent a form which is able with remarkable rapidity 

 to reoccupy denuded land, made possible by prolonged viability 

 of the seed, by the large numbers of seeds produced and the 

 facility of their dispersal. The lodgepole represents a species 

 which by reason of its own power to reproduce is usually pre- 

 vented from attaining great age and maximum dimensions. The 

 density of the stands, the resinous character of its tissues, and 

 the habitats which it often seeks on high and exposed ridges 

 make lodgepole peculiarly susceptible to fires which often re- 

 peatedly sweep the same area. During at least the earlier period 

 of its development the lodgepole stand is often as effective a 

 barrier to the movements of neighboring species as a lake or a 

 snowfield, for stands of trees six to eight feet in height may be 

 so dense as wholly to exclude even the most tolerant of the 

 lesser green plants. In older stands which have begun to open 

 there is, however, opportunity for the entrance of competitors 

 and in some places the white pine may be seen making headway 

 under the much older growth of the lodgepole. Under conditions 

 favoring the entrance of other species the lodgepole must ulti- 

 mately become supplanted. Whitford has found in the forests 

 of the Flathead Valley the invasion of the lodgepole stand by 

 white pine, lowland fir, Engelmann spruce and occasionally ar- 

 bor vitae and western hemlock. If the seeds of western larch, 

 Douglas spruce, or other species of rapid growth in height are 



