A 15-yr (2006-2020) experiment testing factorially-arranged combinations of fire seasonality (summer, fall, spring) and fire return interval (2, 3, 6-yr) plus non-burned controls was conducted in northern mixed prairie to evaluate effects on Hesperostipa comata. Plots were 20-by-15 m with 3 replicates per treatment. Summer fires were conducted during summer quiescence, fall fires after a <-2.2oC frost and spring fires when Bouteloua gracilis initiated growth. Current-year aboveground biomass was estimated annually by clipping four 0.25-m2 quadrats from each plot during peak biomass. Biomass samples were dried to a constant weight at 60°C and weighed to the nearest 0.01 g before being separated into current and past years’ growth and reweighed to determine current-year biomass as an estimate of productivity.