[Chap. LIU THE VEGETATION OF NORTH AMERICA 



755 



and northwestern part, and there the topography is comparatively 

 smooth or rolHng. Most of the area, however, consists of stream-dissected 

 high and low plateaus and mountains, with a great diversity of under- 

 lying rocks and residual soils adjoined by low plains. 



F^ic;. 381. General view of the mixed deciduous forest of the Pisguh National Forest 

 of North Garolina. Photo from U. S. Forest Service. 



The most extensive communities of the deciduous forest on the up- 

 lands and slopes are the mixed hardwood, mixed oak, oak-hickory, white 

 oak, oak-maple-linden, beech-maple, and southward the beech-magnolia. 

 Interspersed among these upland types are the lowland forests of willow- 

 cottonwood-sycamore, elm-ash-maple, and swamp oak-hickory. On ridge 

 tops, cliff edges, gravel hills, and sand plains there are pioneer com- 

 munities of scrub, pitch, and short-leaf pines, either singly or in combi- 

 nation. Usually associated with them are scrub oaks as undergrowth, 

 and various tree oaks that eventually replace them on the better sites. 



