292 THE NORTH AMERICAN GRASSLAND 



The most distinctive dominant of the Palouse prairie is Agropyrum 

 spicatum, together with its variety inerme. Its usual associate is Poa 

 scabrella secunda, a smaller bunch grass of the intervals; it is often 

 mixed with Stipa comata, S. occidentalis, or Koeleria in large quantity, 

 or the first two of these may form small consociations. Agropyrum 

 paucifiorum, A. smithi, and Elymus condensatus, singly or together, are 

 often associated with A. spicatum, though Elymus is most abundant 

 in pure stands in valleys, often of alkaline nature. With the exception 

 of Festuca idahoensis, which usually mingles with Agropyrum at 

 higher elevations, the remaining dominants are generally of rather less 

 abundance or are more or less localized. It is significant of this asso- 

 ciation that the grasses are almost exclusively northern in origin and 

 distribution. 



Subdominants. The principal societies and clans of the typical 

 Palouse prairie of Washingi:on and Idaho have been listed by Weaver 

 (cf. Clements, 1920) ; Lupinus and Astragalus are both well repre- 

 sented, while composites belonging chiefly to the genera Balsamorhiza, 

 Wyethia, Solidago, Carduus, Agoseris, and Aster are the major con- 

 tributors to the estival and serotinal aspects. Piper (1906:51) has 

 found that the subdominants have been derived from three different 

 sources and listed them as belonging to the flora of California, the 

 Rocky Mountains or the Columbia Basin (cf. Taylor, 1911; Taylor 

 and Shaw, 1929). 



Proclimaxes. By far the largest portion of the Palouse prairie 

 today is characterized by sagebrush, Artemisia tridentata, frequently 

 with one or more of its major associates, namely, Atriplex, Chryso- 

 thamnus, or Purshia. This assumes the form of savanna, which is 

 almost indistinguishable from the true sagebrush climax, over exten- 

 sive areas in which the grass dominants have been destroyed. How- 

 ever, all sources of evidence combine to establish the fact that this 

 is a disclimax produced by overgrazing, as in the case of Larrea in the 

 desert plains or Prosopis in the coastal prairie. This relation was 

 established two decades ago by the discovery of prairie relicts through- 

 out the region wherever protection against grazing had existed since 

 the period of settlement, and especially in cemeteries. It is confirmed 

 by scientific record of nearly forty years ago (J. C. Merriam, 1899) 

 and by stockmen of the region who had been attracted to the John 

 Day vallej^ by the fine grassland more than sixty years since. Finally, 

 the field observations upon the dominance of the grasses under pro- 

 tection and the success of sagebrush under heavy grazing have been 

 verified by the results obtained by means of exclosures and by the 

 removal of sagebrush. 



