COASTAL PRAIRIE 279 



bunch form, only Agropyrum, Buchloe, and Hilaria making a close 

 turf. 



Subdominants. The coastal prairie is even richer in perennial forbs 

 that constitute aspect societies than is the true prairie. This is to be 

 ascribed chiefly to the longer growing season and higher temperatures, 

 though somewhat better water relations doubtless play a part. The 

 general harmony between the two is well demonstrated by the fact 

 that of the 90 major subdominants of the true prairie, 75 take a similar 

 role in the coastal association. In addition, there are a considerable 

 number of species of southern or southeastern range that belong to the 

 same genera, e.g., Baptisia, Petalostemon, Salvia, Liatris, Silphium, 

 etc., as well as a score of genera peculiar to the south, such as Atam- 

 asco, Cooperia, Herbertia, Berlandiera, Engelmannia, etc. 



Proclimaxes. As would be expected from the presence of several 

 short grasses, the coastal prairie is converted into a disclimax by over- 

 grazing just as in the mixed prairie. The dominants most concerned 

 are Buchloe, Hilaria, and Bouteloua texana, together with the alien 

 Cynodon dactylon. This change has naturally occurred earlier and 

 most completely in the west and north of the area, but it has moved 

 steadily eastward with increasing grazing pressure. Entirely dis- 

 similar in appearance, but likewise caused by grazing, together with 

 fire, is the disclimax characterized by Prosopis and Opuntia, or by 

 Prosopis and a variety of shrubby associates found in the southwest 

 and in ]\Iexico. Over much of the area of the coastal prairie the two 

 disclimaxes become one, overgi'azing producing a short-grass sod in a 

 savanna of mesquite and cactus. 



Through the central portion of the association, prairie with more 

 or less mesquite alternates with bands of postclimax woodland of 

 oak-hickory, the one found regularly on hard soil or "black land," the 

 other in sandy areas. The woodland belts or "Cross Timbers" are to 

 be regarded as the shrinkage relicts of a former oak-hickory climax, 

 now persisting in sand under a drier climate as a consequence of the 

 compensation afforded by the water relations of this soil. With the 

 occasional exceptions afforded by small denser stands or "motts," the 

 trees have decreased in size and density to the point of forming sa- 

 vanna. The species chiefly concerned is the postoak, Quercus stellata, 

 with which is often associated blackjack, Q. marilandica, and some- 

 times hickory, Carya buckleyi. 



The coast is bordered by a persistent subclimax of marsh varying 

 from 5 to 10 or more miles wide. This receives slow but constant 

 accretions gulfward and passes at a similar rate into the coastal facia- 

 tion of the prairie in the landward direction, slight changes in level 



