CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 



253 



the drought-resistant oak-hickory association, which consequently 

 occurs as a fringe around all the margin of the formation except 

 toward the north. Oak-hickory climax ranges through much of 

 the Piedmont Plateau and the Atlantic and Gulf states coastal plain 

 in an arc that widens westward to eastern Texas. North from east- 

 ern Oklahoma it may become savannah-like where it grades into 

 prairie, but it is more or less continuous to western Minnesota. 



Fig. 125. Typical longleaf pine savannah (Georgia) as maintained by al- 

 most annual burning. Note that the only apparent ground cover is wire grass 

 (Aristida), which is an important factor in facilitating fire— U. S. Forest 

 Service. 



Northwest of the Appalachian center, in unglaciated parts of 

 Ohio and Indiana, oak and hickory occur in combination with 

 numerous other species, forming .a mixed mesophytic forest cli- 

 max, which suggests, by its similarity, that the mixed mesophytic 

 association may still be expanding its range. Throughout the asso- 

 ciation, various combinations of oak-hickory may occur as pre- 

 climax. Postclimax communities of mixed forest may be found 

 within the oak-hickory area on sites, such as old flood plains, where 

 moisture may be exceptionally favorable. 183 Beech, sugar maple, 

 willow oak (Quercus phellos), overcup oak (Q. lyrata), swamp 

 chestnut oak (Q. prinus), and shagbark hickories are indicator 

 species. 



