Paleofire in Southern California over the past 120,000 years

Abstract:

Wildfire events are becoming more frequent and severe in California and other Mediterranean climate regions. Past records of wildfire’s timing, extent and severity can aid our understanding of its role in ecosystems, with charcoal often providing this primary evidence. Charcoal from San Bernardino Mountain lakes over the past 120 kyr had its highest deposition rates during Marine Isotope Stage 3, the Early Holocene, and Late Holocene. These lake records showed varying associations with vegetation and climate change across the glacial-interglacial cycles of the Late Pleistocene. Nonlinear relationships between charcoal deposition and potential drivers, such as ENSO, shrub expansion, and human occupation, persisted into the Holocene. The abiotic and biotic factors that directly influence wildfire are often challenging to discern in the sedimentary record, and process-based ecological modeling offers a complementary approach to better understand these interactions. The La Brea Food Webs project uses this approach to reconstruct the fire regime and vegetation community in the Los Angeles Basin during Marine Isotope Stage 3. Model parameterization relies on Rancho La Brea fossil evidence, including directly-dated plant macrofossils and charcoal. The combination of charcoal and pollen proxy data with quantitative and modelling approaches in ecology are a promising pathway forward to better understand climate-vegetation-wildfire dynamics in Southern California over time.