Holocene History of Desertification along the Woodland-Steppe Border in Northern China

Abstract

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.

Soil aggregate fraction-based 14C analysis and its application in the study of soil organic carbon turnover under forests of different ages

“…Annual mean precipitation is 530 mm with a trend of high in the southeast and low in the northwest, and annual evaporation is 1388 mm that is high in the spring and summer but low in the autumn and winter. The area was once a desert, and climate change is the main driving force for its vegetation degradation [39]. Since the Forestry Center was built in the 1960s, the ecological environment at the site has gradually been restored, now a unique vegetation landscape with forest, shrub, shrubgrassland, grassland, meadow and swamp [40].…”

Timing and spatial distribution of mid‐Holocene drying over northern China: Response to a southeastward retreat of the East Asian Monsoon

“…[12] We identified mid-Holocene dry events through vegetation changes, the termination of soil development and the decline in lake levels [e.g., An et al, 1993;Zhou et al, 2001;Liu et al, 2002;Shi et al, 2002;F.-H. Chen et al, 2003], as these changes are largely related to precipitation . For vegetation records from arid and semiarid regions, the date of increase in desert vegetation (e.g., Ephedra and Chenopodiaceae) was taken as the time of drying [e.g., Zhang et al, 2000], while the date of decrease in broadleaved deciduous/evergreen trees and/or increase in steppe vegetation was selected for those from semihumid and humid regions [e.g., Liu et al, 1992;Yang et al, 1998;Liu et al, 2002;An et al, 2003;Tarasov et al, 2006].…”

“…However, the initiation of mid-Holocene drying varies between sites in northern China, starting between 9000 and 4000 years ago [e.g., An et al, 1993;Chen et al, 1999;Zhou et al, 2001Zhou et al, , 2002Liu et al, 2002;Shi et al, 2002;C.-T. A. Chen et al, 2003;F.-H. Chen et al, 2003;An et al, 2003;Li et al, 2003;He et al, 2004;Jiang et al, 2006]. Clearly, the spatial distribution of the mid-Holocene drying event needs to be identified, not only because this information is crucial to an understanding of climate mechanisms and as a means of defining model boundary conditions, but also because dry events in northern China played a significant role in the collapse and substitution of Chinese Neolithic cultures [Wu and Liu, 2004].…”

Response of forest distribution to past climate change: An insight into future predictions

“…Due to the increase in drought severity, the dominance of oak was gradually replaced by more drought-tolerant pine species, which in turn were eventually replaced by the grassland vegetation [27]. Vegetation evolution during this period was relatively similar to vegetation changes driven by drought in other regions, such as the Mediterranean [31] and the African Sahel region [32].…”

“…Located in a water-stressed region, the vegetation succession pattern of the forest-steppe ecotone in north China during the Holocene also showed four stages dominated by birch, oak, pine and grass [27], but the mechanism of the evolution was not exactly the same as that of the above-mentioned vegetation cycles on sandy dunes. Control of hydrological and thermal conditions by the East Asian summer monsoon intensity was critical for vegetation evolution in China [28][29][30].…”