SOIL GEOCHEMISTRY AND CHARCOAL MORPHOTYPE RESPONSES TO PALEOFIRE IN EILANDVLEI IN THE SOUTH AFRICAN FYNBOS

Fire has the ability to change soil geochemistry, which can facilitate or limit plant growth and may drive changes in dominant vegetation types. In the South African Cape Floristic region, fire is a persistent force occurring multiple times a century. However, the response of soil geochemistry to these frequent, high intensity burns is largely undocumented. Looking at sedimentary archives from Eilandvlei, a small lake on the southern coast of the fynbos, we are working to understand the legacy effects of fires on geochemistry. Specifically, we are exploring the impacts of a high fire frequency regime on soils. Understanding the effects of fire on soil geochemistry will help current land managers develop prescription burning protocols that fit the needs of the land. In this research we examined soil geochemistry and charcoal morphotype changes in response to large magnitude fire events. This research utilizes charcoal influx data to recognize large peak magnitude fire events (>500 particles/cm²/year). We will also use XRF geochemical analysis on sedimentary archives and experimental burning of diagnostic plant species to explore potential responses in soil chemistry and potential changes in vegetation composition, respectively. Using a superposed epoch analysis, we have interrogated the elemental (XRF) time series data between ~4200 BP and ~3200 BP to understand how large magnitude fire events impact sediment geochemistry for years-to-decades following major burning events. Bromine, chlorine and sulfur have shown a statistically significant response 6-8 years after high intensity burns. Sulfur is an important nutrient for plants and the loss could lead to nutrient limitation for some species. We hypothesize that as the geochemical composition of the soil shifts, that there will be a change in the dominant vegetation, analyzed as dominant charcoal morphotypes. After completing experimental burning of extant fynbos plant species we will be able to track the shifts in plant communities that are burning. This project will continue to expand its temporal range with expanding charcoal data and will eventually be able to detect responses over millennia.