Influence of Rainfall and Geography on Leaf Size and Shape: Implications for Paleoclimatic Interpretation

Wesleyan University, Middletown CT

Investigators

Abstract

INFLUENCE OF RAINFALL AND GEOGRAPHY ON LEAF SIZE AND SHAPE: IMPLICATIONS FOR PALEOCLIMATIC INTERPRETATION The leaves of plants are strongly affected by their environment. It is no surprise, then, that the size and shape (physiognomy) of fossil leaves have been used for many decades to reconstruct climatic and ecological conditions of ancient terrestrial landscapes. A new method, called digital leaf physiognomy, has been developed by the PI and colleagues that shows promise for significantly improving paleoenviromental reconstructions compared to existing approaches. However, digital leaf physiognomy presently has two fundamental shortcomings: the current calibration is based on sites with a limited geographic extent and a limited range in rainfall. This restricts the general applicability of the method. This proposal aims to test how climate (both temperature and rainfall) impacts leaf physiognomy in a diverse number of geographic settings using the digital leaf physiognomy approach. Results will be used to construct multivariate models for estimating temperature and rainfall from fossil floras that are more accurate than all existing paleobotanical methods. The models will be applied to a sequence of fossil floras in the Bighorn Basin, Wyoming, to quantify climate across the Paleocene?]Eocene Thermal Maximum (PETM), a critical interval in Earth system history. This proposal will: (1) Test the influence of rainfall on physiognomic variables that have been mechanistically linked to climate; these data will facilitate the construction of new climate proxies and provide a richer framework for understanding the functional ecology of leaf physiognomy. (2) Test potential differences in leaf?]climate relationships in different geographic settings; this test will strengthen the climate proxies and contribute towards understanding the relative influences of phylogeny vs. environment on leaf physiognomy. (3) Reconstruct climate across the PETM; the interpretation of rainfall during the PETM is contentious, yet it is essential for understanding carbon isotope records from fossil soils and the proximal causes of the PETM. Under this proposal, a web data bank for leaf images and associated physiognomic and environmental data will be created; this will serve as an educational source for the general public and as a data source for researchers incorporating leaf images and physiognomic data in ways outside the scope of this project. This proposal will fund 8?]14 undergraduate researchers at Wesleyan, a primarily undergraduate institution, and results from this proposal will be incorporated into Wesleyan courses.