Collapse of fragile Chinese Swamp Cypress forest

The tertiary relict species <i>Glyptostrobus pensilis</i>, formerly widespread in the Pearl River Delta, experienced a sudden decline and was on the brink of extinction in the late Holocene. The mechanism behind is still in debate. Here, using palynological records and principal components analysis, we show that <i>Glyptostrobus pensilis</i> is sensitive to anthropogenic disturbance. Elaborate ¹⁴C results reveal that the forests ended around 2.1 thousand years before the present, with mild contemporaneous climate changes. The presence of burned marks on buried standing stumps suggests that the forests were destroyed by fire, consistent with fire attacks by the Han army during the conquest of the Nanyue Realm in 111 BCE. The swamp preserved the stumps underwater from the fire. Meanwhile, the increases in Poaceae and pioneer plants indicate a boost of human activity after the two conquests during 221 to 111 BCE, as supported by the increases in anthropogenic metal concentrations and population records.