Holocene wildfire history and human activity from high-resolution charcoal and elemental black carbon records in the Guanzhong Basin of the Loess Plateau, China

Abstract

High-resolution sedimentary charcoal and black carbon (BC, including char and soot) records from a loess–soil profile, combined with magnetic susceptibility, δ13C of soil organic matter of analyses, pollen counts and other paleoenvironmental proxies reveal past fire patterns and landscape evolution over the past 12,000 years. Results from the analyses of charcoal and BC influx show that regional fire activity was high in the early and late Holocene, whereas fire was less frequent and pervasive in the middle Holocene. Locally, fires were infrequent near the study site until the Late Holocene. Soot and char analyses do not parallel changes in charcoal variability, and thus appear to reflect either a different aspect of fire activity or else these data are registering aspects of particle transportation and deposition in addition to fire characteristics.The patterns in fire activity observed during the Holocene are consistent with variations in vegetation inferred from δ13C values in soil organic matter, pollen counts, and paleoclimate proxies. Drier and colder-than-present conditions on the Loess Plateau occurred during the Lateglacial and early Holocene (12,000–8500 years BP), which likely enhanced regional fire activity across the Artemisia and Gramineae-dominated steppe landscape in the south of the Loess Plateau. Wetter and warmer-than-present conditions during the mid-Holocene (8500–3100 years BP), reduced fire episodes and promoted the development of mixed forest and forest-steppe. The distribution of C4 plants and woodland expanded at this time from 40% to 60% cover. The subsequent increase in fire-episode frequency during the past 3100 years is consistent with cooler and drier conditions in the late Holocene and also with changes in the spatial and temporal distributions of Neolithic burning practices, such as land reclamation and crop cultivation, during those periods (e.g., expansion of C3 plants).The close association between millennial-scale variations in fire and monsoon activity on the Loess Plateau suggests that future shifts in monsoon-related climate variability could have important consequences for fire and human activities as both respond to regional climate change.