NATURAL AREAS AND REGIONS 



209 



prairies in each of these sections, at 

 2000 ft. in altitude on the western, at 

 3000 ft. in the central and 4000 to 4500 ft. 

 in the eastern section. The high points 

 along the Bitterroot range and in south- 

 western Montana reach 8000 ft. while the 

 principal high ridges vary between 6000 

 and 7000 ft. Ridge elevations in the 

 northern Rockies on the Flathead Na- 

 tional Forest and in Glacier National 

 Park vary between 8000 and 9000 ft. in 

 altitude, the peaks frequently rise to 

 10,000 and 11,000 ft. and have permanent 

 glaciers. This is also true of the forests 

 bordering the Yellowstone Park on the 

 northeast and east. Topography in 

 western Montana and northern Idaho is 

 characterized by very steep canyon 

 slopes and easier grades at the higher 

 levels, indicating a recent uplift. Else- 

 where the general slopes from mountain 

 tops to creek bottoms are more regular 

 and uniform. The southeastern Mon- 

 tana forests center around remnants of 

 an old tableland which rises 1000 to 

 3000 ft. above the rolling plains. 



Aside from the occasional grassland 

 and upper barrens six broad natural 

 forests types exist. These are in their 

 order of altitudinal occurrence, begin- 

 ning with the lowest; western yellow 

 pine ; cedar-hemlock-grand fir-white pine 

 in Idaho; replaced by Douglas fir-western 

 larch in western Montana; Douglas-fir- 

 lodgepole pine in central and eastern 

 Montana; isolated bodies of Englemann 

 spruce in northwestern Montana; and 

 subalpine forests of mountain hemlock- 

 white bark pine, alpine fir and lodgepole 

 pine. 



GRASSLANDS AND PRAIRIES 



The prairies or natural grasslands oc- 

 cur generally below 2000 ft. elevation 

 in Idaho, below 3000 ft. in western 

 Montana and below 4000 ft. in central 

 Montana. The vegetative communities 

 on different 'parts of the Palouse plain 

 in Idaho have been well described by 

 Piper 1 and by Weaver. 2 For description 



1 Piper, Chas. V. "Flora of the State of Washing- 

 ton." Contributions U. S. National Herbarium, XI: 

 38-40. 1906. 



of plant communities in Montana see 

 Harshberger's Phytogeography of the 

 United States. The air temperature over 

 the prairies in summer averages higher 

 than for the lowest forest type. The 

 mean annual temperature for the former 

 in Washington-Idaho is 49.7 and that 

 for the western yellow pine type 47.3. 

 At the same time the prairies show 

 greater extremes of air temperature, 

 lower snowfall, and lower relative 

 humidity than the western yellow pine 

 forests. Precipitation in the western 

 yellow pine type varies between 15 and 

 22 in. per year while that for the prairies 

 averages below 15 in. The total snowfall 

 on the prairies is 17 in. while in the 

 western yellow pine type it is 52 in. 



FOREST TYPES 



Yellow pine type (Transition Zone) 



Western yellow pine (Pinus ponderosa) 

 grows in pure stands at the lower eleva- 

 tion border of the forest: from 1000 ft. 

 altitude up to 4500 ft. in the Clearwater 

 drainage; from 2000 to 4000 ft. in North 

 Idaho generally; and from 3000 to 4000 

 ft. in western Montana. In central 

 Montana the elevations are generally 

 too high for the development of this 

 species. The characteristic open stands, 

 the clear trunks and sparse undergrowth 

 give this forest a park-like appearance. 

 There is more air movement, more sun- 

 light, more heat and less precipitation 

 in yellow pine forests than in the other 

 forest types and therefore more evapora- 

 tion. These conditions, combined with 

 scant humus and litter, result in a soil 

 poor in loam and water-holding capacity. 

 There is invariably more rock and gravel 

 in the soil which causes it to heat by day 

 and cool at night in much greater degree 

 than in other forest types. Deer, coy- 

 otes, squirrels, ground squirrels, pocket 

 gophers, rabbits, pack rats and pheasants 

 are found in this type. 8 



2 Weaver, J. E. "A study of the Vegetation of 

 Southeastern Washington and Adjacent Idaho." 

 Univ. ofNebr. Studies, 17, No. 1, 1917. 



3 For some of the more common plants see: Lar- 

 sen, J. A., "Association of Trees, Shrubs and other 

 Vegetation in the Northern Idaho Forests." Ecol- 

 ogy 4: 63-67, 1923. 



