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Vegetation history in western Uganda during the last 1200 years: a sedimentbased reconstruction from two crater lakes

'Department of Geology, Makerere University, PO Box 7062, Kampala, Uganda; issemmanda{at}sci.mak.ac.ug

David B. Ryves

Environmental History Research Group, Department of Quaternary Geology, Geological Survey of Denmark and Greenland (GEUS), 0ster Voldgade 10, DK-1350, Copenhagen K, Denmark; Department of Geography, Loughborough University, and only from AD 1000 are there clear indications of wide Loughborough, Leicestershire LEl 1 3TU, UK; d.b.ryves{at}lboro.ac.uk

Ole Bennike

Environmental Radioactivity Research Centre, University of Liverpool, PO Box 147, Liverpool L69 3BX, UK; Geological Survey of Denmark and Greenland (GEUS), spread primary forest clearance and secondary forest regener-Oster Voldgade 10, DK-1350, Copenhagen K, Denmark

Peter G. Appleby

Environmental Radioactivity Research Centre, University of Liverpool, PO Box 147, Liverpool L69 3BX, UK

Pollen, plant macrofossil and charcoal records from two neighbouring crater lakes (Lake Wandakara and Lake Kasenda) in lower montane (altitude-1200m) western Uganda (0.5DN, 30) reveal major changes in local and regional vegetation over the last 1200 years, which can be related to regional variations in climate (especially effective precipitation) and human impact. The biological signals are supplemented by evidence from physical sedimentary analyses (magnetic susceptibility, loss-on-ignition, dry mass accumulation rate) for major catchment changes in a wider regional context. From AD 750 to 900, medium-altitude moist forest existed around Lake Kasenda, which was largely replaced by grassland by AD 1000, coincident E _ = with evidence for increased catchment erosion and fire events, linked to human impact during a brief arid phase. Despite wetter conditions from AD 1000 to 1200 and in the 1400s, grassland prevailed around both sites until c. AD 1700-1750, with increased catchment disturbance from AD 1600 to 1700, shortly before the abandonment of major regional settlements and a switch to dispersed homesteads more reliant on pastoralism. A Both sites show the return of semi-deciduous and swamp forest from c. AD 1700 to 1800, with tree and shrub HOLOCENE pollen remaining high until the most recent times. Pollen assemblages reveal increasingly clear human impact RESEARCH on local and regional vegetation in the twentieth century, which obscures any climate signal. Pollen signals may PAPER not be sensitive to all climatic fluctuations (e.g., late eighteenth-early nineteenth-century aridity), but appear to record the varying impacts on vegetation communities of both climate and human activity over long timescales. Other proxies should be analysed to disentangle further the relative importance, and interactions, of these two major drivers of environmental change in tropical Africa in recent millennia.

Key Words: Pollen • macrofossils • charcoal • human impact • climate change • crater lakes • Uganda • East Africa • late Holocene

The Holocene, Vol. 15, No. 1, 119-132 (2005)
DOI: 10.1191/0959683605hl774rp


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