Positive fire-vegetation feedbacks modulated by hydroclimate changes in eastern tropical South America over the last 72 ka
Abstract
The São Francisco basin (SFB) is the largest watershed in eastern tropical South America, encompassing vast areas of savannas, xeric vegetation, and tropical forests. Fire is a fundamental driver shaping ecosystems, yet long-term fire-vegetation dynamics under varying climate conditions in tropical South America remain poorly constrained. Here, we reconstruct 72,000 years of fire and vegetation history in the SFB based on microcharcoal and pollen analyses. Microcharcoal was identified and quantified using an approach combining chemical treatment, Raman spectroscopy for dark-particle identification, slide-scanning, and image analysis. A subset of samples was additionally analyzed for pollen to provide a long-term perspective on vegetation change. Our results show that fire activity was linked to the expansion or contraction of open savannas, which were both modulated by hydroclimate changes driven by orbital- and millennial-scale variability. Observed fire responses in the marine record were driven primarily by fire activity in the central regions of the SFB, which encompass the main burned areas associated with savannas. Modern analyses of the SFB support this interpretation, showing that savannas between 10 and 15°S experience fire activity more than ten times higher than that of adjacent SFB dry or humid forest areas. The most intense fire regime, between 32 and 22 ka, coincided with the maximum expansion of C4-dominated grasslands likely due to enhanced precipitation seasonality associated with a low obliquity phase. At millennial timescales, increased precipitation during Heinrich stadials generally suppressed fire activity through enhanced fuel moisture. Most intervals of increased moisture availability and reduced seasonality were associated with weakened fire regimes, pointing to a predominant fuel-moisture limitation in the basin. These findings also indicate that fire activity across the SFB positively responded to grassland expansion over the analyzed period and highlight the strong sensitivity of fire-vegetation feedbacks to hydroclimate variability across distinct timescales.
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BibTeX
@article{akabane2026positive,
title = {{Positive fire-vegetation feedbacks modulated by hydroclimate changes in eastern tropical South America over the last 72 ka}},
author = {T.K. Akabane and A.L. Daniau and P.E. de Oliveira and D.S. Duarte and V. Hanquiez and A. Romero-Ramirez and Alain Queffelec and M.C. Campos and V.R. Mendes and M. Georget and C.M. Chiessi},
journal = {Global and Planetary Change},
year = {2026},
month = sep,
doi = {10.1016/j.gloplacha.2026.105715},
url = {https://hal.science/hal-05753604v1},
note = {CC BY},
}
RIS
TY - JOUR
TI - Positive fire-vegetation feedbacks modulated by hydroclimate changes in eastern tropical South America over the last 72 ka
AU - T.K. Akabane
AU - A.L. Daniau
AU - P.E. de Oliveira
AU - D.S. Duarte
AU - V. Hanquiez
AU - A. Romero-Ramirez
AU - Alain Queffelec
AU - M.C. Campos
AU - V.R. Mendes
AU - M. Georget
AU - C.M. Chiessi
PY - 2026
DA - 2026/09/17
JO - Global and Planetary Change
DO - 10.1016/j.gloplacha.2026.105715
UR - https://hal.science/hal-05753604v1
AB - The São Francisco basin (SFB) is the largest watershed in eastern tropical South America, encompassing vast areas of savannas, xeric vegetation, and tropical forests. Fire is a fundamental driver shaping ecosystems, yet long-term fire-vegetation dynamics under varying climate conditions in tropical South America remain poorly constrained. Here, we reconstruct 72,000 years of fire and vegetation history in the SFB based on microcharcoal and pollen analyses. Microcharcoal was identified and quantified using an approach combining chemical treatment, Raman spectroscopy for dark-particle identification, slide-scanning, and image analysis. A subset of samples was additionally analyzed for pollen to provide a long-term perspective on vegetation change. Our results show that fire activity was linked to the expansion or contraction of open savannas, which were both modulated by hydroclimate changes driven by orbital- and millennial-scale variability. Observed fire responses in the marine record were driven primarily by fire activity in the central regions of the SFB, which encompass the main burned areas associated with savannas. Modern analyses of the SFB support this interpretation, showing that savannas between 10 and 15°S experience fire activity more than ten times higher than that of adjacent SFB dry or humid forest areas. The most intense fire regime, between 32 and 22 ka, coincided with the maximum expansion of C4-dominated grasslands likely due to enhanced precipitation seasonality associated with a low obliquity phase. At millennial timescales, increased precipitation during Heinrich stadials generally suppressed fire activity through enhanced fuel moisture. Most intervals of increased moisture availability and reduced seasonality were associated with weakened fire regimes, pointing to a predominant fuel-moisture limitation in the basin. These findings also indicate that fire activity across the SFB positively responded to grassland expansion over the analyzed period and highlight the strong sensitivity of fire-vegetation feedbacks to hydroclimate variability across distinct timescales.
SN - 0921-8181
ER -