The modern pollen–vegetation relationships of a tropical forest–savannah mosaic landscape, Ghana, West Africa

Adele C.M Julier,Phillip E Jardine,Stephen Adu-Bredu,Angela L Coe,Akwasi Duah-Gyamfi,Wesley T Fraser,Barry H Lomax,Yadvinder Malhi,Sam Moore,Kennedy Owusu-Afriyie,William D Gosling

doi:10.1080/01916122.2017.1356392

Abstract

ABSTRACTTransitions 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.

Highlights

The transition between closed-canopy forest and open-canopy savannah vegetation is one that can be observed at the present day along climate gradients, and in the fossil record during periods of climatic change (Mayle et al 2007; Azihou et al 2013; Miller & Gosling 2014; Miller et al 2016)
To facilitate a better understanding of transitional periods in fossil pollen records, this study has explored modern pollen– vegetation relationships on a landscape scale within the forest–savannah transition zone in tropical West Africa
This work has demonstrated that by using modern pollen traps deployed within vegetation plots, differences can be identified between the pollen assemblages produced by three vegetation types within a Forest–Savannah transitional mosaic landscape

Summary

Introduction

The transition between closed-canopy forest and open-canopy savannah vegetation is one that can be observed at the present day along climate gradients, and in the fossil record during periods of climatic change (Mayle et al 2007; Azihou et al 2013; Miller & Gosling 2014; Miller et al 2016). The identification of transitional ecosystems in the fossil record may be crucial in providing evidence to support efforts to conserve biodiversity, especially if the persistence of these transitional areas can be demonstrated over long time scales. Fossil pollen records of forest-to-savannah transitions can serve as a guide to the likely future vegetation response; it has been difficult to observe forest-to-savannah transitions in the fossil pollen record because of a poor understanding of how they are represented. Anemophilous taxa, and zoophilous taxa with ‘messy’ pollination syndromes (open flowers with extruded anthers) are generally over-represented relative to their abundance in the vegetation, whereas those zoophilous taxa with more closed floral morphologies are more often underrepresented or palynologically silent (present in vegetation but not pollen assemblages) (Bush & Rivera 2001)

Methods

Results

Discussion

Conclusion