TY - JOUR
T1 - Vegetation history in western Uganda during the last 1200 years: a sediment-based reconstruction from two crater lakes
AU - Ssemmanda, Immaculate
AU - Ryves, David B.
AU - Bennike, Ole
AU - Appleby, Peter G.
PY - 2005/1
Y1 - 2005/1
N2 - Pollen, plant macrofossil and charcoal records from two neighbouring crater lakes (Lake Wandakara and Lake Kasenda) in lower montane (altitude ∼1200 m) western Uganda (0.5°N, 30°E) 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 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. Both sites show the return of semi-deciduous and swamp forest from c. AD 1700 to 1800, with tree and shrub pollen remaining high until the most recent times. Pollen assemblages reveal increasingly clear human impact on local and regional vegetation in the twentieth century, which obscures any climate signal. Pollen signals may 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.
AB - Pollen, plant macrofossil and charcoal records from two neighbouring crater lakes (Lake Wandakara and Lake Kasenda) in lower montane (altitude ∼1200 m) western Uganda (0.5°N, 30°E) 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 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. Both sites show the return of semi-deciduous and swamp forest from c. AD 1700 to 1800, with tree and shrub pollen remaining high until the most recent times. Pollen assemblages reveal increasingly clear human impact on local and regional vegetation in the twentieth century, which obscures any climate signal. Pollen signals may 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.
KW - Charcoal
KW - Climate change
KW - Crater lakes
KW - East Africa
KW - Human impact
KW - Late Holocene
KW - Macrofossils
KW - Pollen
KW - Uganda
UR - http://www.scopus.com/inward/record.url?scp=12544256774&partnerID=8YFLogxK
U2 - 10.1191/0959683605hl774rp
DO - 10.1191/0959683605hl774rp
M3 - Article
VL - 15
SP - 119
EP - 132
JO - Holocene
JF - Holocene
SN - 0959-6836
IS - 1
ER -