Is this duff? Long-term prescribed burning effects on litter and duff in pine flatwoods of the southeastern US

Abstract Background Mapping surface and ground fuels is key to supporting wildland fire research and management. Fuel loading, structure, distribution, and continuity, along with other factors, strongly influence fire spread and consumption. It is, therefore, essential to understand drivers of fuel accumulation such as the aboveground tree inputs from abscission, dispersion, decomposition, disturbances, and management practices (e.g., prescribed fire), particularly in fire-dependent forest ecosystems such as longleaf flatwoods savannas of the southeastern US. In 2022, we collected and measured litter load, duff load, and duff depth before and after prescribed burning in 72 field plots at pine flatwoods at Osceola National Forest, in northern Florida, where a long-term experiment on fire return intervals (FRI; 1, 2, 4 years and unburned controls) has been running since 1958. We assessed how FRI, proximity to trees, wind direction, and structural attributes such as stand basal area and density influenced the distribution and accumulation of litter and duff. Results Overall, litter and duff were highly variable across FRI and before and after prescribed fire. Litter load, duff load, and duff depth all increased with longer FRIs and higher basal area. Consistent prescribed fire significantly increased duff bulk density—defined as the ratio of duff load to duff depth—compared to the long-unburned plots. Proximity to the tree bole was a significant factor explaining duff distribution within unburned plots, while both duff and litter were evenly distributed across the four cardinal directions. Conclusions The FRI of the prescribed burning drove the inter-stand-level accumulation of duff and litter while aboveground tree biomass influenced intra-stand distribution. Consistent prescribed fire resulted in more compacted duff layers, an effect that warrants consideration in carbon assessment in fire-maintained forest ecosystems. This study advances our understanding of litter and duff accumulation dynamics in southern pine flatwoods under frequent prescribed fire management; however, comparison with data from other study sites is essential to corroborate these trends.