THE IMPACT OF LANDSCAPE POSITION ON POST-FIRE SOIL CARBON CYCLING (Invited Presentation)

With ongoing climate change, the role of fire in ecosystems is changing, with implications for vegetation recovery, soil functioning, and human health. Much research has focused on the direct impact of fire on soils, but most prior studies have not explicitly considered the roles of erosion and landform position in dictating the fate of soil carbon (C) post-fire. In particular, the formation and deposition of pyrogenic carbon (PyC) is a significant impact of fire, as this form of soil C is more persistent than other soil organic matter components, and the ability to manage it may help mitigate the effects of climate change. In this related series of studies, I will show that the interaction of burn severity and erosion can introduce significant variation in the composition of soil organic matter and PyC and their long-term persistence. In a field-scale erosion study, I measured sediment production across different slope and burn severities. The highest sediment production was found in the steepest slopes with the highest burn severity, and the greatest production and transport of PyC was in the highest burn severity sites. To probe the fate of this eroded material, PyC produced in the laboratory furnace at two temperatures (350 °C and 500 °C) was incubated in soils from eroding and depositional landform positions. I found significant higher rates of decomposition of soil C and PyC in incubates with the lower temperature chars and depositional soils. The depositional soil had a finer texture and higher water holding capacity, along with more organic matter, that make it more likely to support higher rates of decomposition. Together, these studies indicate that higher burn severity sites may produce more aromatic PyC that is less susceptible to erosion, when fire-affected soil is deposited in depositional environments the rate of decomposition is higher with lower burn severity PyC. The complexities of post-burn landscapes control both erosion potential and decomposition of soil C, which can have significant impacts on soil C accounting at the landscape scale.