Chemotaxonomy as a tool for interpreting the cryptic diversity of Poaceae pollen

The uniform morphology of different species of Poaceae (grass) pollen means that identification to below family level using light microscopy is extremely challenging. Poor taxonomic resolution reduces recoverable information from the grass pollen record, for example, species diversity and environmental preferences cannot be extracted. Recent research suggests Fourier Transform Infra-red Spectroscopy (FTIR) can be used to identify pollen grains based on their chemical composition. Here, we present a study of twelve species from eight subfamilies of Poaceae, selected from across the phylogeny but from a relatively constrained geographical area (tropical West Africa) to assess the feasibility of using this chemical method for identification within the Poaceae family. We assess several spectral processing methods and use K-nearest neighbour (k-nn) analyses, with a leave-one-out cross-validation, to generate identification success rates at different taxonomic levels. We demonstrate we can identify grass pollen grains to subfamily level with an 80% success rate. Our success in identifying Poaceae to subfamily level using FTIR provides an opportunity to generate high taxonomic resolution datasets in research areas such as palaeoecology, forensics, and melissopalynology quickly and at a relatively low cost

The modern pollen-vegetation relationship of a tropical forest-savannah mosaic landscape, Ghana, West Africa

Transitions between forest and savannah vegetation types in fossil pollen records are often poorly understood due to over-production by taxa such as Poaceae and a lack of modern pollen-vegetation studies. Here, modern pollen assemblages from within a forest-savannah transition in West Africa are presented and compared, their characteristic taxa discussed, and implications for the fossil record considered. Fifteen artificial pollen traps were deployed for 1 year, to collect pollen rain from three vegetation plots within the forest-savannah transition in Ghana. High percentages of Poaceae and Melastomataceae/Combretaceae were recorded in all three plots. Erythrophleum suaveolens characterised the forest plot, Manilkara obovata the transition plot and Terminalia the savannah plot. The results indicate that Poaceae pollen influx rates provide the best representation of the forest-savannah gradient, and that a Poaceae abundance of >40% should be considered as indicative of savannah-type vegetation in the fossil record

Modern pollen studies from tropical Africa and their use in palaeoecology

Modern pollen studies are valuable for the calibration of pollen records and contribute to the understanding of past vegetation dynamics. Here, we present a qualitative review of available published and (where possible) unpublished modern pollen studies conducted in tropical Africa since pollen analysis emerged as a discipline in the early 20th century. At present, 318modern pollen rain studies are geographically unevenly distributed across the continent. We found that most countries across tropical Africa have some modern pollen records, with East African countries being particularly well represented in both older and more recent literature. Many countries, arid regions and transitional phytochoria, however, require further study. This review is intended to guide palaeoecologists and palynologists embarking on new studies by bringing together the history of modern pollen studies conducted to date. Targeting new studies to areas where data are currently lacking will help to build a better understanding of modern pollen deposition on the continent. Moreover, we provide recommendations for designing studies so that their results can be used in quantitative modelling techniques for climate or vegetation reconstructions