The Pleistocene biogeography of eastern North America: A nonmigration scenario for deciduous forest

Abstract

8ECFIVEDThe current reconstruction of the vegetation of eastern North America at the last glacial maximum postulates a very wide zone of tundra and boreal forest south of the ice. This reconstruction requires that the deciduous forest retreated far to the south. We believe that this reconstruction is seriously in error. Geologic evidence for glacial activity or tundra is absent from the southern Appalachians. Positive evidence for boreal forest is based on pollen identifications for Picea, Betula, and Pinus, when in reality southern members of these genera have pollen that cannot be distinguished from that of northern members. Further, pollen of typical southern species such as oaks and hickories occurs throughout profiles that past authors had labeled boreal. Pollen evidence for a far southern deciduous forest refuge is lacking. Data on endemics are particularly challenging for the scenario in which deciduous forest migrated to the south and back. The southern Appalachian region is rife with endemics that are often extreme-habitat specialists unable to migrate. The previously glaciated zone is almost completely lacking in endemics. Outlier populations, range boundaries, and absence of certain hybrids all argue against a large boreal zone. Our new reconstruction postulates a cold zone no more than 75-100 miles wide south of the ice in the East. South of this cold zone, the drop in temperature may have shifted species abundances but was not sufficient to remove species growing there today. This new reconstruction has implications for the existence of refugia, for estimates of species climatic tolerances, for testing general circulation models of climate, and for estimates of plant migration rates.

Chloroplast DNA variation in planted and natural regenerated stands of black locust (Robinia pseudoacacia L.)

“…The distribution area of black locust was not covered by ice during the last glacial maximum. LOEHLE and ILTIS (1998) listed black locust as a tree species whose northern ranges stop at the ice margin. Refugees and a migration history as were detected for many tree species in Central Europe are lacking.…”