MIXED PRAIRIE 263 



Muhlenbergia montana, are southern in distribution ; others are north- 

 ern or in high altitudes, as with Carex stenophylla, Festuca ovina, or 

 Koelcria. By contrast with the bunch grasses, the sod-formers have 

 become relatively more abundant since the advent of overgrazing, and 

 it appears probable that Buchloe at least has spread more widely. 

 Differences in distribution within the mixed prairie are reflected in its 

 structure, and hence its subdivisions or faciations form a series ir- 

 regularly parallel from north to south. 



Subdominants. The number of subdominants or perennial forbs 

 that characterize the aspect societies or sociations is large, though 

 considerably less than in the true prairie. The abundance of indi- 

 viduals is likewise reduced, both features being consequences of the 

 competition for a lower water content due to a lessened rainfall. The 

 subdominants of the first importance amount to a score or so, of which 

 three-fourths occur in the region from Canada to Texas and an equal 

 number are found also in true prairie. The chief species of the pre- 

 vernal aspect is the common pasqueflower, Aneinone patens, together 

 with Leucocrinum montamim and Townsendia sericea, and these are 

 followed by Senecio aureus, Oxytropis lajnberti, and early species of 

 Astragalus. The estival period is marked by Psoralea tenui flora and 

 Malvastrum coccineum in particular with Petalostenion candidus, P. 

 purpureus, Oenothera serrulata, Lupinus argenteus. Verbena bipinnati- 

 fida, Castilleia integra, and species of Astragalus and Pentstemon 

 widespread and important. The serotinal aspect is characterized by 

 composites, of which the most abundant are Aster multijiorus, A. can- 

 escens, Artemisia dracunculus, A. indgaris, Liatris punctata, Solidago 

 missouriensis, Chrysopsis villosa, Kuhnia glutinosa, and Grindelia 

 squarrosa. ]Most conspicuous of all are Artemisia frigida, Gutierrezia 

 sarothrae, and Amphiachyris dracunculoides, but these are indicators 

 of the disclimax due to overgrazing. 



Proclimaxes.^ The mixed prairie contains two postclimaxes, 

 namely, fioodjilain woodland and tall grass, and one omnipresent dis- 

 climax, the so-called short-gi'ass plains. The first two are to be re- 

 garded as relicts of former climaxes, the fringing woodland being a 

 mere fragment of an earlier and much more extensive deciduous for- 

 est. The tall-grass community not only forms meadow in the stream 

 valleys, but also covers large areas of sandhills and river dunes and 

 persists likewise on foothills and escarpments. Three species of An- 

 droi)ogon, namely, furcatus, ?u(tans, and scoparius, are more or less 



1 The term proclimax is used for all communities that suggest something of 

 the permanence or extent of a climax, but are not controlled by climate. Those 

 that originate and are maintained by disturbance are disclimaxes. 



