Habitat-related error in estimating temperatures from leaf margins in a humid tropical forest

Leaf margin characters are strong predictors of mean annual temperature (MA T) in modern plant communities :Ind widely used tools for reconstructing pa leoclimates from fossil floras. However, the frequency of nonentire-margine d species may vary dramatically between different habitats of the same fore st. In this paper we explore the potential for this habitat variation to in troduce error into temperature reconstructions, based on field data from a modern lowland forest in Amazonian Ecuador. The data show that the provenance of leaves can influence temperature estim ates to an important degree and in a consistent direction. Woody plants gro wing along lakes and rivers underestimated MAT by 2.5 degrees -5 degreesC. while there in closed-canopy forest provided very accurate predictions. The high proportion of liana species with toothed leaves in lakeside and river side samples appears to be I responsible for a large part of the bias. Samp les from closed-canopy forest that included both lianas and trees, however, were more accurate than tree-only or liana-only samples. We conclude that paleotemperature reconstructions based on leaf margin char acters will he misleading to the extent that fossilization provides a bette r record of certain habitats than others. The preponderance of lake and riv er deposits in the angiosperm fossil record suggests that underestimation o f mean annual paleotemperature may be common.