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Widespread reforestation before European influence on Amazonia

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Science  30 Apr 2021:
Vol. 372, Issue 6541, pp. 484-487
DOI: 10.1126/science.abf3870

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Pre-Columbian reforestation in Amazonia

An early 17th-century temporary reduction in global atmospheric carbon dioxide (CO2) levels has now been attributed to reforestation in Amazonia after the catastrophic loss of life of the indigenous population caused by diseases brought by European invaders. Using fossil pollen data from Amazonian lake sediments with temporal resolution over the past millennium, Bush et al. found that forest recovery began 300 to 600 years before the population crash. The more recent nadir in atmospheric CO2 was not associated with rapid reforestation at that time. The vegetation changes appear to be the result of changing patterns of land use in the centuries preceding the European arrival and the resulting devastation, whereas the cause of the CO2 decline remains enigmatic.

Science, this issue p. 484

Abstract

An estimated 90 to 95% of Indigenous people in Amazonia died after European contact. This population collapse is postulated to have caused decreases in atmospheric carbon dioxide concentrations at around 1610 CE, as a result of a wave of land abandonment in the wake of disease, slavery, and warfare, whereby the attendant reversion to forest substantially increased terrestrial carbon sequestration. On the basis of 39 Amazonian fossil pollen records, we show that there was no synchronous reforestation event associated with such an atmospheric carbon dioxide response after European arrival in Amazonia. Instead, we find that, at most sites, land abandonment and forest regrowth began about 300 to 600 years before European arrival. Pre-European pandemics, social strife, or environmental change may have contributed to these early site abandonments and ecological shifts.

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