Anthropogenic impacts on vegetation and biodiversity of the lower Yangtze region during the mid-Holocene

Human perturbation and its impact on vegetation and plant diversity during the Holocene have caused serious concerns for the biogeological and geoarchaeological communities. As a centre of origin of rice agriculture, the lower Yangtze region (LYR) has a long history of human occupation over most of the Holocene. However, early anthropogenic impacts on the ecosystem of the region remain elusive. Here we present a multidisciplinary study including pollen and charcoal analysis on three different sediment cores (TJA, YJ1503 and PW) along a gradient of human interference to disentangle human and climatic influences on vegetation in the coastal area of the LYR. The results show that rice farming which developed after an environmental transition from salt marsh to freshwater wetland was mainly assisted by fire, particularly slash-and-burn practices by the Neolithic people between 7 and 4 kyr BP. Both the vegetation composition and plant diversity of the mixed forests of the LYR responded to these early human perturbations with a threshold effect. However, whereas plant diversity rapidly recovered when human activity ceased/weakened, the vegetation composition showed differences from the pre-fire condition, indicating a lasting effect. We propose that the varied post-fire recovery strategies of different species, e.g. Quercus evergreen comp. versus Pinus massonania, would account for this discrepancy.