Abstract
Microcharcoal is a proxy of biomass burning and widely used in paleoenvironment research to reconstruct the fire history, which is influenced by the climate and land cover changes of the past. At present, microcharcoal characteristics (amount, size, shape) are commonly quantified by visual inspection, which is a precise but time-consuming approach. A few computer-assisted methods have been developed, but with an insufficient degree of automation. This paper proposes a new methodology for microcharcoal statistical analysis based on digital image processing by ImageJ software, which improves statistical efficiency by 80–90%, and validation by manual statistical comparison. The method is then applied to reconstruct the fire-related environmental change in the Weiyuan loess section since about 40 thousand years before present (ka BP), northwest China with a semi-arid climate, found that the microcharcoal concentration is low in cold and dry climate and high in warm and humid climate. The two main contributions of this study are: 1) proposal of a new, reliable and high efficient automatic statistical method for microcharcoal analysis; and 2) using the new method in a semi-arid section, revealing the paleofire evolution patterns in the semi-arid region was mainly driven by the biomass rather than the aridity degree found in humid regions.
Highlights
Fire is an important ecological factor that can indicate changes of climate, vegetation and human activities
The Weiyuan section can be divided into the following several layers (Figure 1B) (Yang X et al, 2015): 1) 0–20 cm: cultivated layer, disturbed by human planting activities; 2) 20–135 cm: paleosol (S0), developed under a warm and wet climate during the Holocene (11.7-0 ka BP), corresponding to marine isotope stage 1 (MIS 1); 3) 135–555 cm: loess (L1-1), developed under a cold and dry climate during the Last Glacial Maximum (26.520 ka BP, MIS2); 4) 555–680 cm: loess (L1-2), a weak paleosol developed during an interstadial of the Last Glacial Period (MIS 3, 57–32 ka BP), under a warmer and wetter climate
As an important proxy reflecting the occurrence of fire events, microcharcoal has a unique research value; manual statistical analysis of microcharcoal contents is time-consuming, which hinders the application and development of this method
Summary
Fire is an important ecological factor that can indicate changes of climate, vegetation and human activities. With the frequent occurrence of extreme weather events, the incidence of biomass burning has increased (Jolly et al, 2015). This has had significant impacts: ecological damage, economic costs, and human casualties (Ashe et al, 2009; Goldammer et al, 2013), for Microcharcoal Automatic Statistics and Palaeoenvironment example, the 2019–2020 Australian bushfire season (colloquially known as the Black Summer) (Campbell et al, 2020; Lindenmayer and Taylor, 2020). Climate dynamics and vegetation variations operate at relatively larger scales than fire processes (Macias Fauria et al, 2011), which are considered to be the primary control factors of the fire (Moritz et al, 2005). Understanding past fire dynamics and their relationship to environmental factors is a key aspect of preserving and managing present-day ecosystem functions and fire occurrence (Conedera et al, 2009)
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