The Blufflands: Pleistocene Pathway into the Tunica Hills

Reinvestigation of the evidence for disjunctions of northern plant species in the Tunica Hills of southeastern Louisiana and adjacent southwestern Mississippi reveals that, rather than serving as an isolated island refugium, these hills represent the southernmost extension of the Blufflands. This study documents the distributions in the southeastern United States of 10 plant species previously considered disjunct in the Tunica Hills by as much as 800 miles from the N. These species occur primarily in the Appalachian Mountains, the Ozarks and northward, and extend into Louisiana along the Blufflands. The Blufflands, a belt of hilly land bordering the eastern escarpment of the Mississippi River alluvial valley, coincide with the thickest accumulations of loessial sediments in the Tennessee-Mississippi-Louisiana area. The cold, glacial meltwater-fed Mississippi River and associated dense, cold air mass funneled past the Blufflands during maximum continental glaciations. We postulate that contact of cold river water and accompanying air mass with relatively warmer air produced extensive advection fogs along the Blufflands, supplying moisture and cooling the uplands bordering the Mississippi River. These conditions promoted the southward migration of numerous species of the Mixed Mesophytic Forest at least along the Bluffland pathway. Erosion of the loess into vertical ravines has maintained cool, moist habitats within the Bluffland hills suitable for the continued relict existence of many northern plant species. The causal mechanism presented here for the southward migrations of Mixed Mesophytic Forest species along all major river systems of the Southeast during the late Pleistocene adequately accounts for documented distributions of northern disjunct plant species (of those species associated with mesic deciduous woodlands) in the southern Atlantic and Gulf coastal plains. In addition, this mechanism allows for the persistence of Tertiary endemics in the Appalachians through the Pleistocene and Holocene.