Integrating charcoal morphology and stable carbon isotope analysis to identify non-grass elongate charcoal in tropical savannas

Rehn, Emma, Rowe, Cassandra, Ulm, Sean, Woodward, Craig, Zawadzki, Atun, Jacobsen, Geraldine, and Bird, Michael I. (2021) Integrating charcoal morphology and stable carbon isotope analysis to identify non-grass elongate charcoal in tropical savannas. Vegetation History and Archaeobotany. (In Press)

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Abstract

Fire is inextricably linked to the vegetation that provides the fuel load. For palaeofire records to contribute meaningfully to the reconstruction of past landscape fire history, it is helpful to identify the vegetation that has been burnt, for example, grassy versus woody vegetation in tropical savannas. The morphological characteristics of charcoal particles can provide useful information on source vegetation type, and the aspect ratio of charcoal particles has been proposed to identify the contribution of grasses to environmental records. Stable carbon isotope analysis of pyrogenic carbon can also chemically identify the proportion of C3 and C4 biomass in charcoal samples but has yet to be widely applied alongside charcoal morphological analysis. Using carbon isotope analysis we demonstrate that C3 sedges contribute elongate charcoal to a fire record where C4 grasses are absent. These results challenge the widespread assumption that elongate charcoal is primarily or exclusively derived from grass, as most experimental studies demonstrating this relationship were conducted in environments where graminoids (grass-like forms) did not significantly contribute to available fuels. In turn, this complicates the simple interpretation of elongate aspect ratios for charcoal in fire records as direct proxies for the proportion of grasses in an environment, beyond differentiating temperate forests from grasslands. Minimal work to date has been done on separating charcoal derived from different graminoid types and future studies would benefit from the ability to differentiate graminoids including Poaceae and Cyperaceae in fire records. These results highlight the benefits of a multi-proxy approach to the interpretation of fire records in tropical savannas.

Item ID: 67930
Item Type: Article (Research - C1)
ISSN: 1617-6278
Keywords: Charcoal morphology, Pyrogenic carbon, Stable carbon isotopes, Palaeofire, Savannah, Northern Australia
Copyright Information: Published Version: (C) © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021. Accepted Version: Open Access in an Institutional Repository after a 12 month embargo.
Funders: ARC Centre of Excellence for Australian Biodiversity and Heritage (ACR), Australian Institute of Nuclear Science and Engineering (AINSE)
Projects and Grants: ARC FL140100044, ARC CE170100015
Research Data: http://doi.org/10.25903/5de5f1e48e86d
Date Deposited: 19 Jul 2021 01:40
FoR Codes: 37 EARTH SCIENCES > 3703 Geochemistry > 370303 Isotope geochemistry @ 30%
37 EARTH SCIENCES > 3709 Physical geography and environmental geoscience > 370905 Quaternary environments @ 30%
43 HISTORY, HERITAGE AND ARCHAEOLOGY > 4303 Historical studies > 430307 Environmental history @ 40%
SEO Codes: 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 50%
28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280111 Expanding knowledge in the environmental sciences @ 50%
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