[Chap. LIU THE VEGETATION OF NORTH AMERICA 759 



hemlock-hardwood formation. These plants became established when 

 the climate was cooler and the uplands adjoining the bogs were clothed 

 with spruce, fir, pine, hemlock, and northern deciduous trees. 



In protected coves and rock gorges there are localities with interesting 

 mixtures of trees, shrubs, and herbs, some of which antedate the last 

 glaciation, while others are relicts of postglacial time, when the hemlock- 

 hardwood forest extended much farther westward into Kentucky and 

 Indiana. 



A third type of relict community was represented in the prairie open- 

 ings that the pioneers found in the deciduous forests from western Penn- 

 sylvania and New York to Illinois and western Tennessee. These were 

 remnants of a period drier and warmer than the present, during which 

 prairies extended much farther eastward than at the time of settlement. 



On the Atlantic coastal plain are both relicts of southern plants that 

 extended far northward in preglacial times and remnants of northern 

 vegetation that extended farther south when moraines were being built 

 on Long Island bv the continental glaciers. 



Southeastern evergreen forest (Figs. 385-387). The most conspicuous 

 feature of the Atlantic and Gulf coastal plains is the prevalence of pine 

 barrens. There is no abrupt change eastward from the Piedmont region, 

 or southward from the Cumberland and Ozark plateaus toward the Gulf. 

 One merely passes from regions predominantly oak, with pines on over- 

 drained and infertile sites and on abandoned farms, to regions where 

 pines were the dominant forest trees and oaks either formed the under- 

 growth or occupied the scattered areas of good soil and sites protected 

 from fires. 



Long-leaf, loblolly, slash, and short-leaf pines are the most important 

 species. Long-leaf was the best source of lumber, as well as of resin and 

 turpentine. Loblolly predominated northward and is the weed tree of 

 old fields and cut-over lands of the inner coastal plain, just as slash pine 

 is the weed tree near the coast and on the northern half of the Florida 

 peninsula. The short-leaf pine occurs not onlv on the inner coastal plain 

 but also far inland, from Pennsylvania to Missouri, either scattered 

 among the oaks or in pine forests on shallow, poor soil. 



On the overdrained, sandy, and leached soils are the dry pine barrens, 

 with open stands of pine either alone or with an understory of various 

 oaks. Where trees are scattered and oaks infrequent because of repeated 

 fires, there is often a ground cover of grasses. Near the south coast are 

 the moist and wet pine barrens, in which slash and lon^-leaf occurred 



