Collaborative Research: Savanna Pyrogenic Carbon Dynamics: Patterns and Processes

Wildland fires are changing in complex ways, increasingly threatening the health and economic livelihood of the American public. Although forest fires loom large in the public imagination, savanna ecosystems actually account for almost 70% of global burned area. Crucially, savanna fires produce up to 80% of the world’s fire-derived pyrogenic carbon (PyC)—a highly resistant, charcoal-like material that can potentially trap carbon in soils. A better understanding of PyC in savannas is essential for assessing the contribution of savanna fire to the global carbon cycle, as well as for informing land managers’ objectives for prescribed burns. This project will apply a novel biogeochemical approach to study what environmental factors control how much PyC is produced and how well it is preserved. To achieve this, the research team will study and compare distinct savanna sites in the United States and South Africa. This research will directly benefit society by bridging between scientific discovery and practical land fire management in savanna ecosystems. By combining results from this study with insights from fire professionals, the team will develop practical guidelines that enable fire managers to factor long-term carbon storage into their conservation and restoration goals. The work outlined in this proposal will provide a quantitative and mechanistic foundation for understanding the factors influencing PyC accumulation patterns (Objective 1) and the processes controlling PyC turnover (Objective 2) in savannas. A novel biogeochemical framework will be applied to analyze and compare labile, semi-labile, and stable pools of PyC in tropical and temperate savannas. To examine accumulation patterns, researchers will leverage a long-term monitoring network in Kruger National Park, South Africa, and spatially sample soils covering a diverse array of gradients, including fire, vegetation, and soil texture, to pinpoint the critical drivers of PyC storage. To examine turnover processes, researchers will leverage long-term prescribed fire experiments in Kruger (71 years) and at the Nachusa Grasslands (39 years) in Illinois, USA. PyC production (ƒPyC+) will be measured during active fires, and repeated in-situ sampling will be conducted between fire events, alongside lab incubation experiments, to distinguish between soil physical preservation and microbial degradation mechanisms that determine PyC loss (ƒPyC-). The parameters produced in this project will be incorporated into the ORCHIDEE-SPITFIRE model, the fire-enabled land surface component of the IPSL Earth System Model. Ultimately, these modelling results will be used to explicitly estimate of whether global savanna fires are a net sink or source of terrestrial carbon, as well as when, where, and how the balance is positive or negative. This project will also help develop the next generation of scientific professionals by providing research opportunities and hands-on training, including in the national priority areas of biotechnology and artificial intelligence (AI), for a postdoctoral scientist, a graduate student, and several undergraduates. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.