The Citronelle Formation of south Alabama contains the only fossil plants from the mid-Pliocene Epoch (~3 million years ago) in eastern North America. Fossil plants were first described from this formation in 1916, and no additional research on this flora has been conducted since that time. Preliminary investigations by the PI and students indicated that the Citronelle Formation still contains a rich record of fossil plants, which now includes over 70 newly discovered species. These include fossil leaves, seeds, fruits, and pollen of many plants still living in the area, and many are the oldest records. Important forest trees such as the Southern Red Oak, Green Ash, River Birch, Ironwood, Eastern Cottonwood, and many others have been documented. This flora also includes the last records of plants now extinct in North America but still living in Europe and Asia, such as the water caltrop (Trapa) and the Chinese wingnut tree (a relative of hickories and walnuts). A significant component of the research will include the continued collection and analysis of such plants along with a consideration of their biogeographical importance. This flora is also significant in dating from the so-called mid-Pliocene warm interval. This time represents a relatively recent episode of intense global warmth and, therefore, provides some indication of the possible effects of future global warming on the vegetation of this region. The fossil plants will be analyzed using recent techniques that have been shown to demonstrate correlations between plant structure, climate, and atmospheric carbon dioxide levels. These include co-existence analysis, study of the relationship between leaf shape and climate (physiognomy), and stomatal analysis (i.e., the relationship between the number of gas exchange openings in leaves and atmospheric carbon dioxide levels). The stomatal analysis will provide data toward resolving the controversy over the relative importance of ancient carbon dioxide levels vs. changes in oceanic circulation patterns as the most likely causes of mid-Pliocene warmth. The proposal also includes significant educational and public outreach initiatives.
