Response of vegetation to Holocene evolution of westerlies in the Asian Central Arid Zone

Abstract

Based on 50 pollen sequences inferred from the westerlies-influenced Asian Central Arid Zone, we reconstructed the Holocene vegetation dynamics of four forest types indicated by Picea, Betula, Pinus sibirica and Pinus sylvestris as well as steppe type by Artemisia and desert type by Chenopodiaceae. The sensitivities of these vegetation types to Holocene temperature and precipitation changes were analyzed according to four grouping: temperature, precipitation, latitude and elevation of sites. The results revealed that there was a clear delay of forest expansions in the early Holocene along the S-N gradient, most likely influenced by the existed permafrost extent in the Northern Hemisphere. The increasing precipitation driven by the westerlies in the early Holocene would have first reached the threshold for forest expansion in high-elevation sub-region, but was significantly delay for low-elevation sub-region. Steppe expanded in low-elevation and highland sub-regions in the cooling and wetting late-Holocene. Holocene vegetation dynamics differed across vegetation types with Pinus sibirica and Pinus sylvestris that were very sensitive to westerlies-associated precipitation changes, while Picea and Artemisia were more sensitive to temperature changes. A decreasing sensitivity of forests was found with different types following an evident increase in precipitation and an increasing sensitivity for steppe was observed following a gradual reduction of temperature in the late Holocene. Our research offers new insights into the mechanisms of individualistic responses of plant types and the different responses of vegetation to the Holocene westerlies evolution in the Asian Central Arid Zone and improves our ability to predict the vegetation dynamics (particularly forest) in the Asian Central Arid Zone under global warming conditions.