Variation in modern pollen from tropical evergreen forests and the monsoon seasonality gradient in SW India

This study analyses the pollen signature of tropical lowland forests (< 1000 m a.s.l.) in the Asian monsoon climate. Its aim is to investigate how well the pollen data can reproduce the vegetation patterns in tropical India, and how the variations in the pollen composition are related to the gradient of decreasing plant moisture availability (measured by the ratio of actual over equilibrium evapotranspiration) that is associated with the strong seasonality of precipitation that characterizes the monsoon climate regime. We used canonical correspondence analysis (CCA) to relate the variations in the pollen composition of 71 surface soil samples from evergreen and semi-evergreen forests distributed along the western coast of south India (8degrees 48' N-15degrees 08' N), with the climate characteristics of the sampling sites. We show that variations in plant moisture availability strongly determine variations in the pollen composition; for example evergreen and semi-evergreen forests can be distinguished on the basis of their pollen assemblages. Variations in the mean temperature of the coldest month associated with elevation also determine distinct pollen assemblages; for example ever-green forests above 800 m a.s.l. present different pollen signatures than those below this altitude/temperature limit. Variations in the relative abundance of some pollen taxa are strongly related to plant moisture availability and taxa indicators of climate can be identified. Hence, modern pollen assemblages from tropical forests in south India carry considerable information about vegetation patterns and climate. Paleoclimatic changes, notably in the monsoon season, could be quantified.