East Asian monsoon modulated Holocene spatial and temporal migration of forest-grassland ecotone in Northeast China

Robust forecasts of ecological transformations resulting from ongoing and future climate change are urgently needed. Paleoecological records of vegetation dynamics, combined with records of past climate, can contribute to these forecasts, but the relationship between vegetation and climate is often poorly understood. We synthesized a phytolith dataset using >500 topsoil samples and 6 sedimentary profiles from temperate Northeast China. The modern topsoil dataset was calibrated to quantitatively estimate tree cover and grass cover. Based on the threshold of tree cover, we explored the spatial and temporal variations of the forest-grassland ecotone in NE China as well as possible driving mechanisms. Phytoliths provided reliable quantitative estimates of tree/grass cover, accurately distinguishing sites that are currently forest from grassland in this temperate region. The forest grassland ecotone expanded westward from 7 to 5 ka, retreated eastward from 4 to 2 ka, and then expanded westward again, migrating <100 km throughout this period. The interval of maximum tree cover varied spatiotemporally from east to west during the Holocene. Precipitation from the East Asian summer monsoon was likely the dominant driver of spatial and temporal variations in the forest-grassland ecotone in NE China, with lesser contributions from the Westerly Jet.