Reconstructing grassland fire history using sedimentary charcoal: Considering count, size and shape

Area of Science:

• Earth System Science
• Paleoecology
• Fire Ecology

Background:

• Grassland fires constitute 80% of annual fire activity, yet reconstructing past fire regimes is challenging due to difficulties in interpreting charcoal signals.
• Accurate quantification of past grassland fire regimes requires assessing charcoal count and shape.

Purpose of the Study:

• To improve reconstructions of grassland fire regimes by evaluating charcoal count and shape as proxies.
• To test the relevance of charcoal count by examining factors influencing it, including fire regime components, vegetation, and climate.
• To assess the utility of charcoal width-to-length (W:L) ratio as a proxy for fuel types in grassland environments.

Main Methods:

• Quantified charcoal particle count in 51 sediment samples from Great Plains ponds.
• Examined 13 factors influencing charcoal count, such as fire frequency, area burned, fire season, vegetation, and climate variables.
• Quantified the W:L ratio of charcoal particles and compared it with vegetation cover and pollen assemblages.

Main Results:

• Grassland fire charcoal particles are smaller than forest fire particles; a 60μm mesh is recommended over 120μm for grasslands.
• A W:L ratio of ≤0.5 indicates specific fuel types when grassland vegetation exceeds 40%.
• The area burned within 1060m of depositional sites significantly correlated with charcoal count and area.

Conclusions:

• Charcoal analysis, with adjusted mesh sizes and W:L ratio interpretation, provides a reliable method for reconstructing grassland fire regimes.
• Changes in charcoal count and area over time reflect alterations in the area burned.
• Long-term charcoal records can characterize grassland fire regimes, incorporating human and climatic influences.