TRUE PRAIRIE 269 



The great quantity of droppings of the herds of bison is well indicated 

 by the fact that early settlers found dry buffalo chips their principal 

 source of fuel. These dry portions were what was left after this ma- 

 terial had afforded sustenance for numbers of insects, and shelter in 

 the dry state for tenebrionids and various crickets. 



TRUE PRAIRIE 



Nature and Extent. The designation of the easternmost association 

 of the grassland as true prairie was made originally upon both eco- 

 logical and historical grounds and appears still to be well warranted 

 by the facts. It was inevitably that portion of the climatic grassland 

 with which trapper and pioneer first came in contact and to which the 

 word prairie was regularly applied, the "plains" then being regarded 

 as essentially different. Ecologically, it differs from the mixed prairie 

 by the absence of the lower layer of short grasses, as it does also in 

 being less xeric. Not infrequently the postclimax of tall grasses has 

 been mistaken for true prairie, but, with the exception of the sub- 

 climax border and "openings" of the deciduous forest, it is a disclimax 

 produced by the disturbances accompanying settlement and develop- 

 ment (Clements, 1934, 1936; cf. Shimek, 1911; Transeau, 1935) 

 (Fig. 62). 



True prairie once occupied the entire region between the mixed 

 prairie and the forest to the east, which belonged, for the most part, 

 to the oak-hickory climax, but today it is represented only by small 

 and scattered relicts in the corn and wheat belts of the Middle West. 

 Its western boundary was that of the ecotone between it and mixed 

 prairie, as indicated on page 260; its eastern limit was formed by the 

 subclimax tall grass along the forest edge. This extended from south- 

 ern INIanitoba diagonally through Minnesota to southwestern Wiscon- 

 sin and included the northern two-thirds or more of Illinois and part 

 of northwestern Indiana. The true prairie includes northern and west- 

 ern Missouri and the eastern half of Oklahoma for the most part, pass- 

 ing into the coastal prairie in the region of the Red River. Its major 

 contacts are with the mixed prairie along the entire front of the latter 

 and with the narrow and somewhat interrupted band of postclimax tall 

 grasses that confront the forest. In extent, true prairie ranks second 

 among grassland associations, being surpassed only b}' the mixed 

 prairie. Characteristic grassland animals such as the striped ground 

 squirrel and badger occurred in scattered eastern prairie islands 

 (Fig. 63). 



Climate. The true prairie differs from the mixed chiefly in being 

 more humid, the rainfall along its southeastern boundary from Okla- 



