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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



ing influences on the microenvironment of the 

 Northern Plains mixed grass prairie. 



In the 1970 season, a study for comparing mi- 

 croenvironmental factors in grazed and ungrazed 

 native mixed grass prairie was begun on a 35- 

 acre piece of native grassland at the Dickinson 

 Experiment Station in southwestern North Da- 

 kota. 3 The area included a 4-acre exclosure that 

 had not been grazed since 1961 ; the remaining 

 grassland had been grazed heavily in late fall 

 every year since 1957, usually leaving 3-7 cm. of 

 stubble. The grazing history of the area before 

 1957 is unknown, but it apparently had been sub- 

 jected to moderately heavy summer grazing for a 

 number of years. 



The study area is situated on an upland ridge 

 at an elevation of approximately 2.500 ft. (702 

 m.). The. top of the ridge rises about 300 ft. (91 

 m.) above the surrounding land. The surface ma- 

 terials of the study area and its surroundings are 

 part of the Tongue River member of the Fort 

 Union formation of Palecoene age. The soil of 

 the area is mainly Flasher loamy fine sand, but 

 minor differences in the soils may be present due 

 to the effects of slope and exposure of parent 

 materials. 



The Northern Plains mixed grass prairie lias 

 been described by "Weaver and Clements (21). 

 Hanson and Whitman (12) have given detailed 

 descriptions of grassland types in western North 

 Dakota. On the study area Goetz (10) found a 

 total of about 130 plant species. The principal 

 grasslandtype is needle-and-thread-blue grama- 

 sedge. The major grasses in this type are needle- 

 and-thread (Stipa eomata), blue grama (Boute- 

 loua gracilis), and Avestern wheatgrass (Agropy- 

 ron smithii). The sedges, needleleaf sedge (Carer 

 eleocharis), and threadleaf sedge (Carex fl? fo- 

 lia) are also important. These grass and sedge 

 species make up about 80 percent of the total 

 cover of the type. Plains reedgrass (Calamagros- 

 tis inontanensis) « prairie Junegrass (Koeleria 

 cristata), green needlegrass (Stipa viridula). 

 prairie sandreed (Calamorilfa 7o)igi folia), and 

 Sandberg bluegrass (Poa secunda) are important 



3 The experimental area is situated in the SE%XW%. 

 sec. 32, T. 140 N., R. 96 W., 2 miles northwest of Dicldn- 

 son, Stark County, N. Dak. 



secondary grasses. They make up about 15 per- 

 cent of the cover. 



The broadleaved plants (forbs) native to this 

 type of grassland make up about 5 percent of 

 the cover under undisturbed conditions, but these 

 plants increase considerably under heavy grazing 

 with a consequent reduction in the percentage of 

 grasses in the cover. There are virtually no 

 shrubby plants on the study area, and normally 

 the wood}' plants are of little importance in this 

 grassland type. 



The climate of the Northern Plains is char- 

 acterized as continental, semiarid, and subject to 

 the extreme range of variability detailed by 

 Thornthwaite (20), Borchert (3), and Coupland 

 (4)- The longtime climatic averages at the Dick- 

 inson Station (78-year record) show an average 

 annual precipitation of 15.42 inches (39.17 cm.), 

 with April-July precipitation averaging 9.21 

 inches (60 percent of the total), and April-Sep- 

 tember precipitation 12.11 inches (78 percent of 

 the total). Snowfall is generally light. Open-pan 

 evaporation during the growing season has aver- 

 aged 31.90 inches (81.03 cm.). 



The average annual temperature at the Dick- 

 inson Station is 44° F. (6.7° C), with the Janu- 

 ary average 11.0° and July 69.0° F. The Decem- 

 ber-February mean is 13.8° F., and the June- 

 August mean is 65.7° F. The average total wind 

 for the April -September period has been about 

 16,500 miles (26.553 km.). Wind velocity is gen- 

 erally greatest in the spring period of March. 

 April, and May. although tornadic winds of high 

 velocity are experienced occasionally in the sum- 

 mer period. 



Vegetation And Soil Influences 



Grazing greatly reduces the total amount of 

 plant material above the ground surface, as con- 

 trasted to the ungrazed condition, and results in 

 a substantial change in relative proportions of 

 the species in the cover (tables 1 and 2). To ob- 

 tain yields, twelve 0.25-m. --quadrats were clipped 

 every 2 weeks during the growing season. Current 

 season's material was hand separated from the 

 previously produced, standing dead material. Lit- 

 ter from each plot was collected with a vacuum 

 cleaner, oven-dried, ashed, and reported on an 

 ash-free basis. Vegetation on the grazed site was 



