Vegetation responses to mid-Holocene extreme drought events and subsequent long-term drought on the southeastern Inner Mongolian Plateau, China

Abstract

Ecological responses to climate change are strongly regulated by long-term processes, such as changes in species composition and carbon dynamics in soil; therefore, understanding and predicting these processes require long time scale studies. Based on high-resolution lake sediment records of the Angili Nuur Lake from the forest-steppe ecotone at the southeastern margin of the Asian Gobi, we found three pronounced drought events during the mid-Holocene (∼7.0–6.3ka BP, BP means “before present”, where present means 1950 and ka=1000 years) and a subsequent graduate drying trend. During the extreme drought events, lake aquatic system showed strong desiccation and instant salty marsh expansion; whereas regional forest showed strong resilience. During the following long-term drying at millennial scale, broadleaf forest, coniferous forest and steppe successively dominated in this region, in 6.3–4.4ka BP, 4.0–2.7ka BP and since 2.7ka BP, respectively; but the changing dominance between forest and steppe did not match the climate change rate as reconstructed in previous studies, suggesting a lagged and non-proportional change of vegetation type to the range of climate change. The resilience of forest implies a strong buffering effect of biotic and abiotic factors other than climate, probably explained by diverse micro-environments of this mountainous region that allowed forest to survive during the drought spells, and also by gradual soil coarsening that retarded soil field capacity change and nutrient loss. However, under accumulative drying trend, forest was in general replaced by steppe around 2.0ka BP.