Effect of aridity and rainfall seasonality on vegetation in the southern tropics of East Africa during the Pleistocene/Holocene transition

a r t i c l e i n f o Fossil pollen analyses from northern Lake Malawi, southeast Africa, provide a high-resolution record of vegetation change during the Pleistocene/Holocene transition (~ 18–9 ka). Recent studies of local vegetation from lowland sites have reported contrasting rainfall signals during the Younger Dryas (YD). The Lake Malawi record tracks regional vegetation changes and allows comparison with other tropical African records identifying vegetation opening and local forest maintenance during the YD. Our record shows a gradual decline of afromontane vegetation at 18 ka. Around 14.5 ka, tropical seasonal forest and Zambezian miombo woodland became established. At ~ 13 ka, drier, more open formations gradually became prevalent. Although tropical seasonal forest taxa were still present in the watershed during the YD, this drought-intolerant forest type was likely restricted to areas of favorable edaphic conditions along permanent waterways. The establishment of drought-tolerant vegetation followed the reinforcement of southeasterly tradewinds resulting in a more pronounced dry winter season after ~ 11.8 ka. The onset of the driest, most open vegetation type was coincident with a lake low stand at the beginning of the Holocene. This study demonstrates the importance of global climate forcing and local geomorphological conditions in controlling vegetation distribution. Introduction The African Tropics, which today play a major role in the global hydrological cycle, have undergone tremendous changes over the last 20,000 yr (Gasse, 2000). As the distribution of tropical African vegetation is largely constrained by regional hydrology, past climate changes are often associated with reorganizations of biome distribution (Gajewski et al., 2002; Gasse et al., 2008). However, vegetation response to climate change is poorly understood. Southeast African vegetation is particularly sensitive to changes in precipitation and rainfall seasonality (Hély et al., 2006) resulting from complex interac-Changes in regional vegetation recorded in high-resolution lake sediment cores can serve as a useful tool for deciphering long-term as well as abrupt seasonal changes in these important circulation patterns. Though paleoclimate and vegetation records in tropical African during the last glacial termination are in close agreement until ~ 13 ka, changes during the Younger Dryas (YD) interval are unclear and vary regionally (Gasse et al., 2008). In much of North Africa, an abrupt return of aridity is observed resulting from a southward ITCZ displacement, and vegetation cover was greatly reduced (Hooghiemstra, 1988; Zhao et al., 2000). In contrast, rainforests remained significant until the early Holocene in coastal …