The dynamics shifted dramatically when the Han Empire launched an assault on Nanyue.
Following the collapse of the Qin Dynasty, the Han Dynasty rose to prominence after a brief conflict with the Chu Dynasty. Over the next century, the Han referred to Nanyue as a vassal state, periodically demanding tribute. While Nanyue’s rulers sometimes complied, tensions escalated by 111 BCE due to an attempted coup and a spate of assassinations. In response, the Han Emperor dispatched a formidable force of between 100,000 and 200,000 soldiers to attack Nanyue, led by General Lu Bode.
The Han troops advanced from five different directions, ultimately converging near Nanyue’s capital, Panyou, located in the Pearl River Delta close to present-day Guangzhou. In a disastrous decision, a company commander named Yang Pu ordered the city to be set ablaze, leading to catastrophic consequences.
“The fire not only destroyed the city but also spread uncontrollably to the surrounding forests,” detailed Wang and his research team. The cypress trees in the area burned down to the waterline, leaving behind only their submerged stumps.
The brown dots indicate known sites of buried forests, whereas the orange diamonds represent those confirmed to be ancient. The two yellow diamonds highlight the study sites identified by Wang and colleagues.
Credit: Wang et al. 2025
After the Conflict: Fire and Agricultural Transformation
During the invasion, the surrounding landscape of Panyou was largely marshy and populated with cypress trees. This region had been inhabited for millennia, with rice cultivation tracing back approximately 2,000 years. Evidence gathered from peat layers by Wang and his colleagues indicates that the local population engaged in slash-and-burn agriculture, practicing it on a small scale and allowing cypress forests to regenerate after a couple of seasons.
However, these small-scale burns were insignificant compared to the extensive forest fire initiated by Yang Pu, followed by considerable alterations to the landscape.
As the remnants of the cypress trees slowly succumbed to layers of peat, the ancient forest had an unexpected aftermath. The large fauna, including tigers, elephants, and rhinos, that once roamed the area were no longer present. Instead, the pollen grains captured in the layers of clay above the peat signaled a sudden increase in grassy Poaceae plants, which encompass rice, wheat, and barley.
