Forest mosaics, not savanna corridors, dominated in Southeast Asia during the Last Glacial Maximum

Rebecca Hamilton, Noel Amano, Corey J. A. Bradshaw, Frederik Saltre, Robert Patalano, Dan Penny, Janelle Stevenson, Jesse Wolfhagen, Patrick Roberts

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Abstract

The dominant paradigm is that large tracts of Southeast Asia’s lowland rainforests were replaced with a “savanna corridor” during the cooler, more seasonal climates of the Last Glacial Maximum (LGM) (23,000 to 19,000 y ago). This interpretation has implications for understanding the resilience of Asia’s tropical forests to projected climate change, implying a vulnerability to “savannization”. A savanna corridor is also an important foundation for archaeological interpretations of how humans moved through and settled insular Southeast Asia and Australia. Yet an up-to-date, multiproxy, and empirical examination of the palaeoecological evidence for this corridor is lacking. We conducted qualitative and statistical analyses of 59 palaeoecological records across Southeast Asia to test the evidence for LGM savannization and clarify the relationships between methods, biogeography, and ecological change in the region from the start of Late Glacial Period (119,000 y ago) to the present. The pollen records typically show montane forest persistence during the LGM, while δ13C biomarker proxies indicate the expansion of C4-rich grasslands. We reconcile this discrepancy by hypothesizing the expansion of montane forest in the uplands and replacement of rainforest with seasonally dry tropical forest in the lowlands. We also find that smooth forest transitions between 34,000 and 2,000 y ago point to the capacity of Southeast Asia’s ecosystems both to resist and recover from climate stressors, suggesting resilience to savannization. Finally, the timing of ecological change observed in our combined datasets indicates an ‘early’ onset of the LGM in Southeast Asia from ~30,000 y ago.
Original languageEnglish
Article numbere2311280120
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Volume121
Issue number1
Early online date26 Dec 2023
DOIs
Publication statusPublished - 2 Jan 2024

Keywords

  • monsoon forest
  • Southeast Asia
  • Quaternary
  • grassland
  • palaeoenvironmental change
  • ecological regime shift
  • tropical forests
  • Last Glacial Maximum
  • palaeoecology
  • palynology

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