PRECIPITATION ESTIMATES USING LEAVES FROM MODERN SITES IN EASTERN NORTH AMERICA

A database of leaf morphology and climate variables from thirteen modern floral localities along the East Coast of North America has been created to test both temperature and precipitation equations. The floras are located from New Hampshire to southern Florida, and experience mean annual precipitation between 92 cm and 140 cm, and mean annual temperatures between 4.5°C to 22.3°C. The floras belong to a common geographic province and are floristically similar, thus limiting the chance that variation in leaf morphology between floras is due to major differences in topography or phylogeny between sites.

Are the equations that predict precipitation amounts based upon leaf morphology precise enough to differentiate average precipitation between modern sites in Eastern North America? The relationship between leaf morphology and average precipitation has been quantified recently using approaches calculated from modern leaf morphology and climate data. The original equations were created in order to apply to the fossil record for paleoclimate estimates. These equations have not been tested themselves against an independent sampling of leaf morphology from sites with known precipitation and temperature.

Four published equations that predict precipitation from leaf morphological characters were tested on the modern floras sampled to determine the validity of these equations. Initial results show that average absolute error for all approaches ranges from 34.7 cm to 66.2 cm, with a median error ranging from 32.8 cm to 64.1 cm. These results indicate that published methods to determine precipitation amounts are not precise enough to predict and differentiate average precipitation between modern sites in Eastern North America. Perhaps leaf morphological differences between modern sites in Eastern North America are more influenced by differences in temperature than precipitation