PLEISTOCENE ECOLOGY AND BIOGEOGRAPHY 379 



historical integrity of generalized vegetation zones. On this convic- 

 tion I have attempted to map late Pleistocene vegetation zones in 

 two periods (Figs. 2 and 3). They are based on pollen stratigraphy, 

 periglacial geomorphology and scattered plant and animal fossil 

 records. Presumably, such a map will be of more value to the bio- 

 geographer than one based largely on biogeographic evidence that 

 leads to a circular argument. If boreal forest replaced temperate 

 deciduous forest in the Cumberland Plateau and southern Appala- 

 chians, it seems preferable to attempt to establish this fact in terms 

 of pollen analysis, buried soils, and other fossil evidence. 



Modern Vegetation Zones (Fig. 1) 



Dansereau (1951) has stressed the importance of structure to the 

 geographer and general ecologist, a viewpoint that I believe to be 

 profitable also in paleoecology. Reconstruction of forest community 

 composition from pollen data is beset with difficulties, for example in 

 evaluating relative pollen rain among different wind-pollinated 

 species and correcting for underrepresentation of insect-pollinated 

 plants. However, it seems possible to determine structure of the 

 simplest type, to distinguish forest, savanna, and grassland biochores 

 and, within the first, coniferous and deciduous formations (for 

 definitions of these and other vegetational concepts, see Dansereau, 

 1957). The six major vegetation zones or formations in eastern North 

 America include: (1) treeless tundra; (2) boreal woodland or taiga, 

 a savanna formation of needle-leaved trees scattered in a shrub and 

 lichen mat; (3) boreal forest with a continuous canopy dominated 

 by needle-leaved evergreens; (4) temperate forest dominated by 

 broad-leaved deciduous trees and shrubs; (5) temperate prairie and 

 savanna; (6) subtropical savanna of evergreen sclerophylls and tall 

 grasses. These six zones represent arbitrary divisions of an adaptive 

 gradient controlled in general, if not always in detail, by climate. Is 

 it unreasonable to assume that this gradient maintained its struc- 

 tural features and sequence during the glacial periods? 



features have not been worked out carefully for all the species of pine which are, or 

 might be, expected in this area. Thus the allocation of small grains to the boreal species 

 P. bankesiana is premature. (2) Zone M2 from Frey's core LS-2 contains fairly high 

 percentages of oak (about 15%) and hickory (about 10%) as well as some pollen of 

 Taxodium, Nyssa, and other temperate elements. (3) The predominance of pine might 

 be the result of "over-representation" of a species such as P. serolina, which surrounds 

 boggy sites in the southeast today. In other words, oak, hickory, and associated tem- 

 perate plants occurred at sites some distance from the bay lakes but were "swamped- 

 out" by the well-known heavy rain of pine pollen. 



