Recent advances in understanding duff consumption and post-fire longleaf pine mortality

Many longleaf pine stands across the range have suffered decades of fire exclusion, leading to declines in plant and animal biodiversity and complicating restoration and management efforts. Recent research on this topic has focused on the physiological response of overstory longleaf pines and the fuel characteristics of the surrounding forest floor. In small-scale and operational prescribed fires, post-fire pine mortality is tightly linked to basal duff (lowermost fermentation and humus forest floor horizons) consumption and, where present, crown scorch. Pines with substantial duff consumption suffered coarse root carbohydrate drain, a decline in sap flux, and reduced leaf chlorophyll content. Duff consumption in prescribed fires has been linked to duff moisture content, a difficult to predict variable in prescribed fire planning. Duff moisture varies tremendously across the forest floor and within typical burn units. Basal duff dries more rapidly than within-stand conditions. This heterogeneity in duff characteristics is further complicated by the presence of ignition vectors in the forest floor, including woody fuels and intact pine cones. When pine cones are present, ignition of underlying duff is facilitated well beyond assumed moisture thresholds of these fuels. Operational prescribed burns in long-unburned sites should focus efforts on balancing duff consumption with the need to retain overstory longleaf pines.