Jobs & Scholarships

Four thousand years of tropical forest history at Lake Bosumtwi, Ghana.

Supervisors: Dr K.H. Roucoux, Dr T.R. Baker, Dr S.L. Lewis, Dr W.D. Gosling

School of Geography, University of Leeds, Leeds, West Yorkshire, LS2 9JT, UK.
Earth & Environmental Sciences, CEPSAR, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.

This project will use pollen analysis to construct the most detailed record yet of vegetation change in West Africa during the last four thousand years, which will help to answer fundamental questions about current ecological dynamics of tropical rain forests. We are interested in the extent to which tropical forest has been affected by disturbances of climatic or human origin during this interval because this disturbance history could be important in determining current trends of forest development. For example, increasing forest biomass is a trend common to tropical forests in Africa and South America; this could be the result of fertilisation by anthropogenic carbon dioxide emissions, or past large scale forest disturbances from which the forests are still recovering. Understanding the cause of this trend is essential to making predictions about how these forests and their carbon storage capacity will change under different scenarios of future climate change.
This project is based on a sedimentary sequence drilled in Lake Bosumtwi, Ghana. The lake occupies a one million year old meteorite crater situated amidst tropical semi-deciduous forest. The sediments are rich in organic matter, annually laminated in parts, and accumulated sufficiently rapidly to allow decadal scale resolution and detailed chronology. Vegetation in the region is sensitive to climatic change as it is predominantly influenced by the position of the intertropical convergence zone (ITCZ) which crosses the region twice during the year bringing with it monsoon rains. Over the long term, changes in the average position of the ITCZ are thought to change the annual precipitation. During the last glaciations, for example, the ITCZ was located south of its current range leading to drier conditions while during the middle Holocene its more northerly position brought increased annual rainfall.
The project will have two main components: 1) palynological analysis of a sedimentary sequence from Lake Bosumtwi, to produce a detailed vegetation history for the last four thousand years, and 2) analysis of forest plot data with a view to identifying whether vegetational events recorded in the past are consistent with current trends in forest structure, dynamics and composition. There is plenty of scope to modify the project; alternative directions could emphasise either the vegetation history or the modern ecology theme. Laboratory work (pollen analysis and possibly other palaeoecological techniques) and field work (contributing to collection of ecological census data) will be integral to this project.

For further information please contact k.roucoux@leeds.ac.uk and visit www.geog.leeds.ac.uk/postgraduate/ for details of the application procedure and funding opportunities.

References
Anhuf, D. et al. (2006) Paeo-environmental change in Amazonian and African rainforest during the LGM. Palaeogeography, Palaeoclimatology, Palaeoecology 239, 510-527.
Baker, T.R. et al. (2004) Increasing biomass in Amazonian forest plots. Philosophical Transactions of the Royal Society of London B 359, 353-365.
Elegna, H. et al. (2000) Use of plots to define pollen-vegetation relationships in densely forested ecosystems of Tropical Africa. Review of Palaeobotany and Palynology 112, 79-96.
Maley, J. (1991) The African rainforest vegetation and palaeoenvironments during Late Quaternary. Climatic Change 19, 79-98.
Shanan, T.M. et al. (2006) Paleoclimatic variations in West Africa from a record of late Pleistocene and Holocene lake level stands of Lake Bosumtwi, Ghana. Palaeogeography, Palaeoclimatology, Palaeoecology 242, 287-302.