Zizia aurea (L.) Koch (Apiaceae) planted in a tallgrass restoration near Viola, Wisconsin, declined in numbers in randomly assigned plots left unburned or burned in May (41 to 9 and 63 to 30 individuals, respectively), but tripled in numbers in plots burned in August (72 to 209). Fire intensity varied widely, with a nine-fold range in May (86-782 kW/m) and a 49-fold range in August (58-2831 kW/m). In the August burn treatment, Z. aurea was most common in plots experiencing intense fires that cleared most or all ground litter. These same plots harbored 95% of the Z. aurea that flowered in 1996. A separate mowing experiment removed grass canopies to 10 cm, while leaving litter intact. Zizia aurea numbers did not change in plots mowed in May (76 to 77 individuals), but doubled in plots mowed in August (66 to 121). Zizia aurea is strongly favored by fire that simulates the timing of summer lightning fires thought to be common throughout grasslands and savannas of central North America before European settlement.