There is some variation in productivity among 

 ecosystems, due to the site requirements of the species 

 and the soil-moisture-temperature relationships char- 

 acteristic of the sites on which the ecosystems occur. 

 The ecosystems occupying the most highly productive 

 land are Douglas-fir. ponderosa pine, and fir-spruce. 



At the other end of the scale are pinyon-juniper 

 and chaparral-mountain shrub; because of the very 

 nature of these systems and the climatic conditions 

 under which they exist, they cannot produce even 20 

 cubic feet of wood per acre per year. However, the 

 combined 50 million acres of these two types is valu- 

 able for other resource uses. 



In addition, some 11.5 million acres of forest land 

 that is capable of producing 20 cubic feet or more per 

 acre annually is in either a reserved category where 

 timber cannot be harvested, or in a deferred category 

 under study for possible use as wilderness. 



The Great Plains area is dominated by grasses. 



Rangelands 



About half of the rangelands in the United States is 

 in the Rocky Mountains and Great Plains. The 

 rangelands, along with the pinyon-juniper and 

 chaparral-mountain shrub forest ecosystems (which 

 are often included with the rangeland ecosystems), 

 occupy some 458 million acres or 62 percent of the 

 land area of this section (table 2.8). The Rocky 

 Mountains and the Great Plains areas differ greatly 

 in physical and climatic characteristics and corre- 

 sponding differences in rangeland ecosystems. 



The Great Plains area with its hot, dry summers 

 and cold, windswept winters is dominated by grasses 

 — short, medium, and tall. Interspersed within these 

 grasslands are stringers of deciduous forest along the 

 tributaries of the Missouri and Mississippi Rivers. 

 Coniferous forests cover isolated mountain uplifts 

 such as the Black Hills in South Dakota and the Bear 

 Paws in Montana. About 26 million acres of the east- 

 ern part of the Plains are covered with tall grasses of 

 the prairie ecosystem, including big, little, and sand 

 bluestems; switchgrass; and Indian grass with a rich 

 assortment of forbs. To the west, the prairie eco- 

 system gives way to the short and medium grasses of 

 the vast plains grassland, which totals 139 million 

 acres, and is the largest in the United States. The 

 bluestems, switchgrass, and Indian grass are replaced 

 by thickspike and western wheatgrass, green needle- 

 grass, needle-and-thread, blue grama, and buffalo 

 grass. The grasslands also include a large and colorful 

 variety of forbs mostly from the aster, snapdragon, 

 pea, and wild buckwheat families. 



West of the Great Plains is the Rocky Mountain 

 region, a land of contrasts in temperatures, physio- 



graphic relief, and vegetation. Rangelands of this 

 area are usually divided into three general kinds — the 

 foothill and mountain grasslands, the lush mountain 

 meadows and alpine grasslands of the Rockies 

 proper, and the arid and semiarid shrublands and 

 grasslands of the deserts, interior basins, and isolated 

 mountain ranges of the Southwest. 



The mountain grasslands, totaling almost 17 mil- 

 lion acres, are found in all of the Rocky Mountain 

 States. Montana accounts for over two-thirds of the 

 acreage. Bluebunch wheatgrass, needle-and-thread, 

 rough and Idaho fescues, June grass, and oatgrass are 

 the important grasses in the foothills and mountain 

 grasslands of the northern Rockies. In the central and 

 southern Rockies, rough and Idaho fescues are re- 

 placed by Thurbers and Arizona fescue. Forbs make 

 up a large part of the herbaceous vegetation in this 

 ecosystem. Penstemons, larkspurs, lupines, phloxes, 

 vetches, forget-me-not, and brown-eyed susan are 

 colorful components of these ecosystems. 



Mountam meadows and alpine grasslands cap the 

 highest ridges and the flanks of the tallest peaks 

 throughout the Rockies. Bent grasses, tufted hair- 

 grass, sedges of many species, mountain timothy and 

 bluegrasses, many forbs, and patches of dwarf wil- 

 lows provide a close and tight ground cover through- 

 out the alpine area in spite of the short growing sea- 

 son and severe climate common to the area. 



Sagebrush is the second largest rangeland ecosys- 

 tem in the United States. Over 104 million acres, or 

 80 percent of this ecosystem, is in the Rocky Moun- 

 tain area. It is the major vegetation of the Snake 

 River plains of Idaho, the Bighorn and Wyoming 

 Basins in Wyoming, the basins and isolated mountain 



42 



