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The woodland-steppe ecotone of the southeastern Inner Mongolian Plateau in northern China is located at the northwestern limit of the Pacific monsoon influence, where the landscape may have been a sensitive recorder of past climatic changes. Physical, chemical, and biological analyses of AMS 14C-dated sediment sequences from two lakes of this region were used to reconstruct the Holocene vegetation and desertification history and distinguish four periods: (1) a cold and humid period from 10000 to 8000 14C yr B.P., (2) a warm and humid period from 8000 to 5900 14C yr B.P., (3) a warm and dry period from 5900 to 2900 14C yr B.P., and (4) a cool and dry period from 2900 14C yr B.P. to the present. The increased aridity during the middle Holocene was likely caused by increased winter temperatures and enhanced winter evaporation. The transition from a humid to an arid climate after ∼5900 14C yr B.P. coincided with enhanced aeolian activity, and deciduous woodlands were replaced by pine woodlands and then by steppes in response to the climatic deterioration. These transitions led to the present desertification. The records suggest that a simple association of thermal and moisture conditions, such as warm/wet or cold/dry, may be misleading.

The Western Liaohe River Basin in northeastern China is one of the cradles of ancient Chinese civilization. Archaeological records from this region indicate that human occupation began about 8000 years ago and that agriculture and pastoralism were important activities from an early stage. Very little is known, however, about the effects that these activities had upon the landscape. This paper presents the results of a palaeoecological study from a 3.6 m sedimentary sequence in a relict oxbow lake in the Western Liaohe River Basin of southeast Inner Mongolia. The 5400-yr sequence indicates that human activities had a noticeable impact on an apparently open landscape. Buckwheat cultivation began as early as 5400 cal. yr BP with intensification of agricultural activities from approximately 4700 cal. yr BP. Nitrophilous plants such as Solanum and Cerastium, and also Artemisia were growing in the region at certain times, linked with fluctuations in the d 15 N record and probably indicative of increased pastoralism and unintentional/ intentional manuring. Burning was probably used for clearance of the steppe vegetation for agriculture with a close relationship apparent between increased influx of microfossil charcoal and the presence of buckwheat. Superimposed upon this record of human impact is also clear indication of three significant intervals of climate change between 2900 and 2600, 1200 and 600 and 600 and 30 cal. yr BP. The latter two are discussed in relation to the 'Mediaeval Warm Period' and 'Little Ice Age' apparent in sedimentary sequences across the Northern Hemisphere. Discussions are therefore made in terms of the impact that both climate change and ancient Chinese civilizations had upon shaping the present day landscape and vegetation.

Oxygen and hydrogen isotopic compositions of meteoric water are known to correlate with surface air temperature, except in tropical areas. This relationship has been described using a number of terms corresponding to specific observations, such as latitude, altitude and seasonal effects. However, these temperature effects do not seem to apply to precipitation in monsoonal areas of Asia. Questions have been raised as to whether the isotopic composition of meteoric water can be used to reconstruct paleomonsoon intensity. Tree rings of two modern spruce trees (Picea meyeri) and a 10,000-yr-old timber (Picea jezoensis) were analyzed for hydrogen isotopic composition. On average, the older tree is depleted in deuterium by 45‰ compared to the modern trees. We attribute this isotopic depletion to the strength of summer monsoons, which were more intense in the early Holocene than at present. Although this study is not definitive, it suggests that paleomonsoon intensity can be reconstructed by direct or proxy methods that yield the oxygen or hydrogen isotopic composition of meteoric water.