Apr. IS. 1920 Nati've Vegetation of Northern Great Plains 71 



The abundance of a given species often appears greater than is deter- 

 mined by actual counts per unit area. Pound and Clements (4) have 

 fully discussed this point. From Plate 12 it would appear that Psora- 

 lea argophylla is the most abundant species. However, by a number of 

 actual counts per unit area it was found to be fourth in abundance of 

 plants other than grasses and sedges. 



SUMMARY 



(i) The data and conclusions presented in this paper have been 

 obtained in connection with a grazing experiment at the Bureau of Plant 

 Industry Field Station near Mandan, N. Dak. This experiment is 

 designed to determine the carrying capacity of the native vegetation and 

 the effects upon it of different intensities and methods of grazing. 



(2) The vegetation is composed of a large number of species, only a 

 few of which produce a considerable amount of the total forage. The 

 dominating species are Boutelovu gracilis and Stipa comata. 



(3) The density of the vegetation is determined by the thickness of 

 plants upon the ground surface and not by the foliage growth. The 

 term cover used in connection with density may mean basal cover or 

 foliage cover. The former remains after the latter has been removed by 

 close grazing or clipping. 



(4) The total basal cover of all species in the Mandan region is approx- 

 imately 60 per cent of the ground surface. Boutelovu gracilis has a 

 basal cover of about 20 per cent and Stipa comata nearly 10 per cent of the 

 ground surface. 



(5) Clipping data of different day periods showed that Boutelotta gracilis 



had produced from 40 to 50 per cent and Stipa comata from 15 to 20 



per cent of the total forage. The remainder was made up of a number of 



other species. 



LITERATURE CITED 



(i) CuEMENTS, Frederic E. 



1916. PLANT succession; an analysis of the development of vegetation. 

 xiii, 512 p., illus., pi. Washington, D. C. (Carnegie Inst. Washington, 

 Pub. 242.) 



(2) Griffiths, David, Bidwell, George L., and Goodrich, Charles E. 



1915. N.\TIVE pasture grasses OF THE UNITED STATES. U. S. Dept. Agr. Bui. 

 201, 52 p., 9 pi. 



(3) Pound, Roscoe, and Clements, Frederic E. 



1898. A METHOD OP determining THE ABUNDANCE OF SECONDARY SPECIES. In 



Minn. Bot. Studies, s. 2, pt. i, p. 19-24. 



(4) 



1900. THE PHYTOGEOGRAPHY OF NEBRASKA, ed. 2, 442 p., 4 maps. Lincoln, 

 Nebr. (Univ. Nebr. Bot. Survey, no. 8.) Bibliography, p. 22-30. 

 (5) Sampson, Arthur W. 



1914. NATURAL REVEGETATION OF RANGE LANDS BASED UPON GROWTH REQUIRE- 

 MENTS AND LIFE HISTORY OF THE VEGETATION. In Jour. Agr. Research, 

 V. 3, no. 2, p. 93-148, 6 fig., pi. 12-23. 



