Human activities facilitated the decline of forest ecosystem in East Asia after 5000 a BP

Human activities have drastically reshaped global forest ecosystems in recent decades. However, identifying the origins, magnitude, and primary effects of these actions, especially in East Asia (EA), with a long history of human activity, remains challenging. Crucially, unraveling the early anthropogenic impacts on forest ecosystems has substantial implications for characterizing the Anthropocene. In this study, we collated and synthesized Holocene arboreal pollen (AP) sequences from 61 EA lake basins, which demonstrated an overall expansion of forest vegetation during the early to middle Holocene, followed by a retreat from 5 cal. ka BP. The cooling and drying climate during the mid- and late Holocene proved inimical to forest proliferation across EA. Survival imperatives are likely to drive humans to adopt grazing and farming, causing a transformation from forest land to agro-pastoral land. This change further accelerated forest ecosystem degradation. By dividing EA into five subregions, we observed asynchronous declines in forest vegetation from 8 cal. ka BP to 3 cal. ka BP. This trend is primarily attributed to human impacts, given the pronounced coincidence between forest reduction and emergence and prosperity of Neolithic agriculture in each region. Significantly, the positive feedback loop between population growth and agricultural expansion can amplify human impacts. Coupled with climatic effects, these factors resulted in EA's forest vegetation plummeting to its lowest level since 10 cal. ka BP at 2.1 cal. ka BP. Furthermore, the anthropogenic influences on EA forest vegetation mirror land use, soil erosion, and vegetation variability observed globally in terms of timeline. These alterations are driven by human activities, almost coinciding with shifts in atmospheric greenhouse gas levels away from their natural trajectory. We, therefore, argue that the Anthropocene definition should consider the aggregate environmental impact of human activities over millennia, rather than restricting to the most recent centuries.