Effects of prescribed burning on ant-mediated dispersal of Sanguinaria canadensis in Missouri

Ant-mediated seed dispersal (myrmecochory) occurs worldwide, including habitats with frequent fire regimes. This research addresses the effects of prescribed fire on dispersal of the ant-dispersed herb Sanguinaria canadensis in Missouri. We hypothesized ants would remove more seeds farther in burned areas due to reduced leaf litter. During the summer of 2020, we compared the amounts and distances ants dispersed S. canadensis seeds in 36 plots across two sites burned in January & March, 2020, and 37 plots across two control sites (last burned in 2017 and 2018). For two hours per plot, we watched three piles of 20 S. canadensis seeds, piles spaced 1 m apart, and followed seed-carrying ants to determine dispersal distances. Ants transported over twice as many seeds and carried seeds an average of 44 cm farther in burned compared to control areas. The two most common ants, Aphaenogaster rudis and Formica pallidefulva, accounted for 81% of all observed dispersal events, but F. pallidefulva dispersed proportionally more seeds in burned areas. Both species carried seeds farther distances in burned compared to unburned areas, but the magnitude increase was greater for F. pallidefulva. By quantifying the effects of fire on myrmecochory, we show prescribed burning positively affects dispersal of S. canadensis by increasing foraging activity and dispersal distances of the most common dispersers. Future research should test whether these effects also affect seed germination and seedling survival, and whether they extend to other myrmecochorous plants in the Ozarks and other parts of the eastern U.S.