THE SUBCLIMAX PRAIRIE. 133 



dominants of the subclimax run the whole gamut of water-content from wet 

 meadow to true prairie. 



Factor relations. — Because of its ability to grow in saturated soil, Spartina 

 often serves as the last consocies in the wet meadow stage of the bydrosere. 

 During most of the summer, the soil in which it grows is usually moist rather 

 than wet, and this, with its tendency to mix with the other dominants, war- 

 rants putting it in the subclimax for the present. In the regions with more 

 rainfall, it is properly to be regarded as a wet-meadow dominant. It clearly 

 has the highest water requirements of all its associates and is apt to be the 

 most localized, as well as in the purest stands. The water-content of Spartina 

 ranges from saturation to about 45 per cent, while that of Elymus and Panicum 

 is from 60 to 30 per cent. The last two are nearly equivalent, though Elymus 

 will grow in somewhat moister soil. Andropogon furcatus and A. nutans are 

 the most mesophytic of the four Andropogons, and are nearly equivalent to 

 Panicum and Elymus. They form a much more perfect sod than these two, 

 and as a result are more successful in competition and less susceptible to annual 

 fluctuations. The normal range of water-content for A . furcatus is 50 to 25 

 per cent. Andropogon nutans is slightly less mesophytic and A. scoparius 

 still less so, though all three frequently occur together. The water values of 

 A. saccharoides are unknown, but its constant association with A. scoparius 

 in Kansas, Oklahoma, and Texas indicates an intermediate position between 

 this and A. furcatus. Bouteloua racemosa has essentially the same water 

 requirements as A. scoparius, and the two are regularly mixed, not only in the 

 subclimax, but in rough places throughout the prairies, plains, and desert 

 plains. For a more detailed account of the ecological factors, the reader is 

 referred to Thornber (1901 : 32), Weaver (1919), and Pool, Weaver, and 

 Jean (1919). 



Three other species of grasses occur with such abundance or frequence as 

 to require notice, though none of them can be properly ranked as dominants. 

 The most important is Poa pratensis, which displaces the native grasses in 

 many places where grazing, mowing, or other disturbances have given it the 

 advantage. In sandy soils, and especially in sandhills, Andropogon hallii is 

 frequently associated with A. scoparius and occasionally with A. furcatus. 

 Panicum scoparium is abundant throughout the subclimax and also in the 

 transition to the true prairies, but it can hardly be regarded as a dominant 

 because of its low stature. In essence, it is a layer society of the first import- 

 ance, but it is hardly to be treated as an actual society because of its vegeta- 

 tion-form. Its broad leaves, however, do give it much the value of a sub- 

 dominant herb. 



Sequence. — The factor relations of the dominants are confirmed by their 

 topographic position and serai sequence. Hundreds of localities in boldly 

 rolling prairies will show the fundamental sequence from wet meadow to crest 

 of ridge. This is (1) Spartina, (2) Elymus, (3) Panicum virgatum, (4) Andro- 

 pogon furcatus, (5) A. nutans, (6) A. scoparius, (7) Bouteloua racemosa, with 

 Poa pratensis appearing almost anywhere between Spartina and A. scoparius 

 as disturbance permits. In sandy meadows of the sandhill region, disturb- 

 ance often initiates a subsere in which the early grasses are Eriocoma cus- 

 pidata, Andropogon hallii, and A. scoparius, followed by A. furcatus, Panicum 



