210 EXPERIMENT STATION RECORD. [Vol.37 



The grass-steppe is stated to be " a vegetative response t« a low, infrequent 

 rainfall, the greater percentage (approximately 75 per cent) of which comes 

 during the growing season, and about 60 per cent of which is during the four 

 months, June. July, August, and September." The average annual temperature 

 for the steppe area ranges from 45 to 56' F. The relative humidity is generally 

 low, from about 50 to 55 per cent. The grass-steppe is indicative of temperature 

 conditions favorable to a varied agriculture when sufficient moisture is supplied. 



The shrub-steppe, which is scattered throughout the entire intermountain 

 area, and occupies nearly 25 per cent of the area of the State, is as a rule repre- 

 sentative of good general farming and orchard lands. The most important and 

 by far the most extensive vegetation of the shrub-steppe is sagebrush, which is 

 the characteristic type of vegetation of the well-drained, nonalkaline arid dis- 

 tricts of western Colorado. Tjpes of shrub-steppe vegetation of secondary im- 

 portance are greasewood and rabbitbrush, which cover the larger part of San 

 Luis Valley and limited areas in othor parts of the State. Greasewo(xl is not 

 indicative of any particular set of climatic factors, but is a response to local 

 soil conditions. It is, however, almost always an indication of a high water 

 table and consequently of soil rich in alkali. " The round-leaveil saltbush 

 {Atriplex confertifolia). sometimes along with greasewood (Sarcobatus rcrmi- 

 culatin), and common Grayia (Grayia spinosa), is found chiefly on alkaline 

 flats in western Colorado, especially in fhe lower valleys. Extensive and typical 

 areas of this association are found In the lower Snake River Valley. The soil it 

 occupies is usually fine-grained, the surface layers dry. and the soil below the 

 first and second foot quite high in salt content. Salt sage or small saltbush 

 (Atriplrx nuttalli) is another plant of alkaline flats." 



Scrub oak forms the moftt extensive growth of chaparral or brushland and 

 grows under a wide range of climatic conditions as found between 4.0<.X) and 9,000 

 ft. It is frequently associated with buckbrush, and both usually occupy deep 

 rich soil. Scrub oak formg are seldom found above the limit of successful growth 

 of alfalfa, potatoes, small grains, strawberries, hardy can fruits, and the hardy 

 vegetables. 



The pinyon pine-juniper woodland zone is confined to a region of which the 

 mean annual precipitation Is uniformly under 15 In. It is an Index " of temper- 

 ature conditions which permit the growth of all but the tenderest fruits, all the 

 small grains, flax, sugar beets, potatoes, alfalfa, and the garden vegetables, 

 excluding melons. In the lower part of the belt peaches, sweet cherries, melons, 

 And other tender crops yield bountifully. Much valuable orchard land of Colo- 

 rado is cleared pinyon pine-juniper soil." 



Yellow-pine forests seldom show typical development in areas having less 

 tlian 15 in. of precipitation annually. It-s altitude ranges approximately from 

 6,000 to S.OOO ft in northern Colorado and 7.000 to 9.000 ft in southern Colorado. 

 A large percentage of the area of growth of this plant is so steep and stony as 

 to be economically adapted only to grazing and timber growing. Yellow-pine 

 forest indicates temperature conditions favorable to the maturing usually of 

 wheat oats, barley, and rye, and is well suited to alfalfa, potatoes, and the 

 hardier vegetables, cane fruit"?, and strawberries. 



" Ix)dgepole pine, as a strongly developed plant association. Indicates temper- 

 ature conditions too low for the maturing of the small cereals, for the profitable 

 growth of alfalfa, potatoes, peas, and any but the most hardy vegetables." 

 The same is true of the white-fir forest zone. Engelmann fir occupies a region 

 of nonagricultural climatic conditions. 



Weather conditions, 1911-1916 (ilirmesota Sta., Rpt. Crookton Sub.ota., 

 1910-1916, pp. H-19). — Tables are given which .show the precipitation by 

 months and the dates of the latest killing frost in the spring and the earliest 



