Human-driven fires have shaped the Amazonian forest for over 10,000 years

For over 10,000 years, human actions have been shaping the Amazonian forest through the use of fire. A comprehensive study of 1,361 radiocarbon-dated charcoal fragments and archaeological materials reveals that fire in the rainforest is almost exclusively a result of human activity, not a natural occurrence. The findings, published in Frontiers of Biogeography, show that fire in the Amazon has significantly altered vegetation patterns, comparable to major climatic shifts.

Before human arrival, Amazonian fires were extremely rare, with charcoal found only in minuscule amounts at sites like the Hill of Six Lakes in Brazil. The Amazonian landscape remained relatively untouched by fire until humans appeared around 4,500 years ago, introducing fire to a naive ecosystem. The introduction of regular burning by humans fundamentally transformed a stable system that had existed since the late Pleistocene.

Researchers identified three distinct phases of human-driven fire in Amazonia over the Holocene. Between 10,000 and 6,000 years ago, fires were limited to peripheral areas along the Amazon River. Within 6,000 to 4,000 years ago, the geographic spread of fire and occupation sites rapidly expanded across most regions. Finally, between 3,000 and 2,000 years ago, fire reached the deep interior of the basin, transforming an area that had remained relatively fire-free for thousands of years.

Over the last 700 years, there has been a significant two-phase decline in fire frequency. First, fire frequency decreased by 600 to 700 years ago, coinciding with the early abandonment of lands before European arrival. Evidence from lake sediments shows a significant pollen surge during this period, indicating massive reforestation and a shift in land use.

The second phase of decline followed the Great Dying after A.D. 1541, when disease, warfare, and enslavement led to the death of an estimated 90%–95% of Indigenous peoples. This period marked a more extensive phase of forest recovery as ignitions vanished with the population.

The dynamic of human-driven fire patterns in Amazonia over the last two millennia has led to an increase in human-caused fires, accelerating changes in vegetation. This has resulted in a profound ecological imprint, favoring fire-tolerant species such as palms while shaping the configuration of modern Amazonian plant communities.

The restructuring of pyrogeography over the last 2,000 years has likely played a significant role in shaping today's forests, with fire-induced vegetation change comparable to major climatic shifts.