Litter Fall after Wildfire in Virgin Forests of Northeastern Minnesota

The Little Sioux Fire burned virgin forests in northeastern Minnesota on 14–17 May 1971. We monitored litter fall for 3 years after the fire in mixed conifer–deciduous forests both within and outside the fire boundaries. We separated four categories of litter: conifer needles, deciduous leaves, woody material, and miscellaneous material. Significantly more litter fell in the burned area during the 3 years (575 g/m 2 ) than in the unburned areas (340 g/m 2 ). Major differences were related to an increased fall of needles from conifers that had been killed by the fire and an increased fall of woody material from dead trees on the burn. Needles falling from these dead trees had significantly higher concentrations of N, P, and K and lower concentrations of Ca than did needles falling in the unburned areas. No other litter components showed significant differences in concentrations of N, P, K, Ca, and Mg between the burned and unburned areas for the 3 years of the study. By the 3rd year after the fire, less litter fell on the burn than on the unburned area, and the proportion of litter in all components except needles was similar in both areas.