The vegetation and topography of a large part of western 

 North Dakota show considerable heterogeneity (Figure 2-6) and 

 will be discussed in detail here so as to serve as an example of the 

 grouping of species. '^^ In order to unravel relationships between 

 plant groupings and topographic and soil conditions in this 

 region, many stands were analyzed and described. The charac- 

 teristics of frequency, abundance, and herbage cover were chiefly 

 used to measure the degree of success of the plants in the different 

 habitats, and the species were then grouped into nine main 

 community types. The habitats differed in topography, thickness 

 of the surface layer of dark soil, depth at which calcium carbonate 

 showed effervescence with HCl, alkalinity or acidity of the upper 

 horizons, total concentration of soluble salts, amounts of sodium 

 and carbonate, soil texture, and colloidal content. On the upland 

 plateaus and gentle upland slopes with a fairly deep, dark, 

 residual sandy-loam soil (Chestnut group) the chief dominants 

 and constants were Bouteloua gracilis, Stipa comata, Carex Jilifolia, C. 

 stenophylla, Agropyron smithii, and Koeleria cnstata. Stands of these 

 and associated species occurring in different areas were sufficiently 



Figure 2-6. Similar communities occur in similar habitats 

 such as plateau tops, long slopes, valleys, and eroding banks. 

 A stand of blue gramagrass-needle-and-thread-sedge com- 

 munity-type appears in the foreground. May, 1959, western 

 North Dakota. (U.S.D.A. Soil Conservation Service.) 



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