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The focus of this paper is on the reconstruction of the mid-Holocene climatic changes based on the pollen records contained in a 6.2 m thick section in the southern part of the Tengger Desert, northwestern China. To understand the modern analogues of the mid-Holocene changes, modern pollen spectra across different vegetation zones from the Qilian Mountains to the lowland Tengger Desert were studied first. Four pollen combinations were identified, corresponding to four different modern ecological environments: (1) a Picea-Artemisia combination in a spruce forest and its vicinity; (2) an Artemisia-Chenopodiaceae-Gramineae-Salix combination in a mixture belt of montane grassland and poplar woodland; (3) a Chenopodiaceae-Artemisia-Nitraria combination in a desert steppe belt; and (4) an Elaeagnus-Artemisia-Chenopodiaceae-Nitraria combination in a desert riparian forest. Our study also shows that a relatively low percentage of Picea pollen (30–10%) seems to be associated with water transportation (alluvial deposits) and a very low percentage of Picea pollen (10–5%) appears to be related to long-distance air transportation. With references to the modern relationships between pollen assemblages and associated bioclimates, the pollen sequence covering the period between 8500 and 3000 cal. BP was used to infer the climatic change history. The results show that a warmer and drier climate dominated between 8500 and 7950 cal. BP. Subsequent decreases in Artemisia and warm desert forbs/shrubs taxa and contemporaneous fluctuating increases in montane coniferous and aquatics elements from 7950 to 7400 cal. BP reflect a fluctuating increase in humidity and/or a fluctuating decrease in temperature. The following period from 7400 to 5650 cal. BP was generally warm with the Holocene Climate Optimum occurring between 7400 and 6500 cal. BP. A remarkably cool spell followed between 6500 and 6300 cal. BP that was then succeeded by a warmer and more humid period between 6300 and 5650 cal. BP. The period between 5650 and 4450 cal. BP was characterized by drastic oscillations in climatic conditions with three humid and probably cold spells intervened by three relatively dry and warm spells. The period between 4450 and 3500 cal. BP was cold and humid, followed by a wet spell as indicated by a very high percentage of Typha pollen. [ABSTRACT FROM AUTHOR]

Pollen, microscopic charcoal and radiocarbon data are used to document changes in vegetation dynamics during the late Holocene from Namelok Swamp in the Amboseli Basin (Kenya). The data reveal changes in savanna vegetation composition driven by an interaction of climate change, anthropogenic and herbivore activities. The abundance of Celtis, Podocarpus and Syzygium reflects a relatively moist climate from around 3000 to 2400 cal. yr BP. Increased abundance of Acacia, Amaranthaceae/Chenopodiaceae and Poaceae suggest a drier and/or warmer climate from 2150 to around 1675 cal. yr BP. The expansion of Syzygium within the catchment and decrease in Amaranthaceae/Chenopodiaceae reflect a relatively wet phase from around 1675 to about 550 cal. yr BP - superimposed on this is a large increase in Poaceae from 1400 to 800 cal. yr BP indicative of a drier environment. The dominance of Amaranthaceae/Chenopodiaceae and Poaceae with an associated decrease in Syzygium from 550 cal. yr BP is thought to correspond to a drier climate. The uppermost samples, dating to the last 150 years, record a large increase in Acacia, Amaranthaceae/Chenopodiaceae and Poaceae with decrease in Syzygium and are attributed to recent land-use changes associated with increased sedentary settlement. The increased presence of Cannabis sativa, Cereal and Ricinus communis pollen, combined with charcoal in the sediment record, particularly from 2500 but more constantly from 1600 cal. yr BP, indicate a long history of human-ecosystem interaction in the Amboseli Basin that has implications for future management of the area. [ABSTRACT FROM AUTHOR]