PLEISTOCENE ECOLOGY AND BIOGEOGRAPHY 389 



Old World (Deevey and Flint, 1957), little has been added to the 

 Postglacial pollen sequence summarized by Deevey in 1949. The 

 Hypsithermal, also known as Thermal Maximum, Xerothermic, 

 Altithermal, etc., extended with intermittent pulsations from 9,500 

 to 2,000 years ago (Deevey and Flint, 1957). It is the most important 

 climatic event of the period. Documentation of the classic Midwest 

 Prairie Peninsula extension continues with Smith's recent valuable 

 analysis of terrestrial vertebrates (1957). In addition to mapping 

 relict outposts of prairie animals. Smith showed that it is possible 

 to interpret anomalous and otherwise confusing splits in subspecific 

 populations in terms of post-Xerothermic isolation. Instructive 

 examples are found in Agkistrodon contortrix (copperhead), Natrix 

 erythrogasler (copper-bellied water snake), Diadophis punctatus, and 

 Opheodrys vernalis. In a bold and original interpretation Smith 

 explained the history of the Pseudacris nigrita (chorus frog) complex 

 in terms of invasion of P. n. feriarum, the eastern, forest-inhabiting 

 race, by P. n. triseriata, a grasslands form from the west. Post- 

 Xerothermic isolation left a segment of P. n. triseriata, recently de- 

 scribed as P. n. kalmi, in New Jersey and the Delmarva Peninsula. 

 Thus on both sides of the Appalachians separate, isolated, popula- 

 tions of triseriata type chorus frogs integrate wnth feriarum. 



Postglacial pollen diagrams indicate Thermal Maximum (C-2 

 pollen zone) shifts in species composition, with an increase in oak 

 and hickory in southern New England and, locally, of hemlock in 

 northern New England. In many diagrams a recovery of spruce 

 follows in C-3. During the Thermal Maximum Whittaker (1956, p. 

 60) believed that spruce and fir were pinched off the tops of certain 

 mountains in the Smokies. Displacement upward of 1,000 feet or 

 more is indicated by absence of these trees in presumably suitable 

 sites on peaks of less than 5,500 feet elevation. 



Thermal Maximum changes, which command attention of the 

 student of community composition, the evolutionist, and the bio- 

 geographer, were inappreciable in terms of the plant formations 

 mapped in Fig. 1. They do not justify an attempt at a separate 

 vegetation map. 



Western United States, Mexico, and the Tropics 



Exclusion from Figs. 1-3 does not imply that these areas escaped 

 considerable late Pleistocene climatic and environmental change. 

 For the present, however, it seems impossible to express this effec- 



