96 FOREST DISTRIBUTIOX 



diversity. It extends from the benches and plains at 2000 to, 

 3000 feet to the level of eontimioiis forest at -4000 to 6000. It 

 may thus from cne part of the region to another cover a vertical 

 distance of 4000 feet. It is largely the foothill country, varying 

 with exposure and location from arid to humid conditions, inter- 

 rupted and divided here and there by descending extensions 

 of the montane forests. In some places it is the bunchgi-a-ss 

 (Agropyron spp.) or the bunchgrass and sagebrush (Artemisia 

 tridentata, A. cana. A. frigida, etc.) or these merging into open 

 stands of Rocky ^lountain juniper, or yellow pine or Douglas 

 spruce, or all of them intermingled. Again it appears in areas 

 in composition similar to the Pacific Coast Humid Transition 

 with hemlock, grand fir, arbor vitae, western yew and many 

 other forms commonly found in the fortsts of the low lands of 

 western Oregon and Washington. The humid forest is the 

 more rare and is developed where neighboring areas are elevated 

 to the degree necessary to induce condensations and abundant 

 rain, where the valleys are not too wide and where the proximity 

 of considerable bodies of water and the structure of the soil 

 combine to afford the rec[uisite conditions. These are forests 

 of moderate or low elevations, 2000-4000 feet. The forests of 

 the Transition alternate frequently with prairies and the vege- 

 tation of this zone extends in the southern part of ^lontana 

 about 1000 feet higher on the mountain sides than it does in the 

 north, reaching even to 6000 feet. 



The forest of the foothills (Transition) merge gradually 

 into those of the montane (Canadian) belt. Especially in the 

 humid forest is the line of demarcation uncertain. Reference 

 to the tables under the discussion of general aspects of distri- 

 bution will show that in most sections the vertical range of many 

 species may be 2000 to 4000 feet and in different parts of the 

 state some species may be found at altitudes varying from 2000 

 to 9000 feet. The following figures indicate the approximate 

 extent of vertical distribution of the species cf gymnosperms 

 within this region, as far as at present known. . 



