Journal Article

Microcharcoals Reveal More Grass Than Trees During the Mid‐Holocene Optimum on the Chinese Loess Plateau

Zhang, Hongliang, Zhao, Yongtao, Wang, Zisha, Han, Wenxia, Miao, Yunfa, Gao, Changhai, Zou, Yaguo, Lu, Yin, Zhang, Zhigao, Zhang, Ziyue

2023

Overview

Microcharcoal morphology, which changes with biofuel type in the wildfire, can be used as an index for wildfire history and vegetation evolution. Here, five loess sites across the Chinese Loess Plateau were used to establish the biofuel history of the region during the Holocene based on microcharcoal morphological records. The results suggested that consistently increasing grass biofuel dominated the mid‐Holocene (∼7,500–3,000 yr BP), and the grassland or steppe expanded in the same interval. Since the climate conditions with simultaneous high precipitation and temperature of the mid‐Holocene are the most recent paleoclimate analog for future warming, we argue that the humid and warm conditions expected under future global warming on the Loess Plateau might lead to an increase in the grass rather than trees. Plain Language Summary As the product of the incomplete combustion of plants, microcharcoal has been widely used as a wildfire indicator, though microcharcoal morphology has received little attention. Studies have recognized that microcharcoal morphology can indicate the biofuel type (grass or wood) burnt in wildfires and thus can be used as an ideal index in wildfire history and vegetation evolution research. Here, we shed new light on biofuel history based on this established relationship. We compiled 425 microcharcoal records from five sites across the Chinese Loess Plateau and combined the data with compiled pollen records to establish the vegetation history during the Holocene. The results suggest that grassland or steppe was prevalent during the mid‐Holocene, consistent with the synthesized herb pollen records, biome reconstruction, and high precipitation and temperature. Because the climate conditions of the mid‐Holocene are the most recent paleoclimate analog for future warming, we infer that the humid and warm conditions expected under future global warming may promote the expansion of grass vegetation on the Loess Plateau. The insights may reveal the vulnerability of the restoration achievements dominated by plantations today. In addition, we highlight the potential of the more easily preserved microcharcoal to explore vegetation history in future work. Key Points Microcharcoal morphological history reveals that grassland or steppe dominated the mid‐Holocene on the Chinese Loess Plateau The humid and warm conditions under future global warming on the Chinese Loess Plateau might lead to prevalent grass rather than trees Evidence suggests that more native grassland or steppe should be considered in future restoration programs on the Loess Plateau

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Biodiesel fuels / Biofuels / Chinese Loess Plateau / Climate / Climate change / Climatic conditions / Evolution / Global warming / Grasses / Grasslands / History / Holocene / Loess / microcharcoal morphology / mid‐Holocene / Morphology / Paleoclimate / Paleoclimatology / Plateaus / Pollen / Precipitation / Precipitation-temperature relationships / Records / Restoration / Steppes / Trees / Vegetation / vegetation type / Vulnerability / Wildfires