Monsoon-induced errors in paleotemperature estimation based on leaf morphology analysis in central Japan

摘要

Models based on the relationship between leaf morphology and climate parameters of different regions have been used for paleoclimate estimation. Information from Japanese floras has been included in some of these models; however, variation in the distribution pattern of leaf margin within Japan caused by the effect of topography and East Asian Monsoon has not been reflected in these previously published leaf margin analysis models. In this study, we investigate the relationship between leaf characters and climate parameters under different climate conditions within a small geographical scale and, in doing so, improve the accuracy of leaf physiognomy-based paleoclimate reconstruction. We use the local flora in central Japan as an example to determine the distribution pattern of leaf margin (toothed and untoothed) and habit (evergreen and deciduous) characteristics under monsoon climate conditions. In areas along the Pacific Ocean (P-zone), the leaf margin and habit types correlated with the temperature parameters and growing season precipitation. The P-zone includes more toothed species than in other regions of the world obtained with published models at a given mean annual temperature. In the areas along the Sea of Japan (J-zone) with deeper snow cover during the winter, the percent of sub-canopy evergreen shrubs increases, especially at higher altitudes. No significant relationship between leaf margin characters and climate parameters was observed in this area. As heavy snow was a feature of this region since late Early Pleistocene times, paleoclimate estimation based on leaf margin of fossil assemblages younger than Early Pleistocene from these areas might be less reliable. In addition, we found that the leaf margin of woody shrub species is less sensitive to the mean annual temperature than tree species.