Technical Abstract: Fuel and fire conditions needed to cause grass mortality are largely unknown. Individual plants of Hesperostipa comata, Carex filifolia, Bouteloua gracilis, and Pascopyrum smithii were collected from rangeland, potted, and acclimated to greenhouse conditions. Plants were exposed to fire in 1-by-0.5-m burn cages using 500-9000 kg/ha fuel loads in 500 kg/ha increments. Experiment 1 used grass fuel loads ranging from 500 to 4500 kg/ha and showed no plant mortality or tiller loss with increasing fuel loads. Experiment 2 used two fuel load treatments ranging from 5000 to 9000 kg/ha. One fuel type was all grass and the other 3000 kg/ha of grass with the remainder comprised of Artemisia cana. Soil surface temperatures were recorded every second during fires using thermocouples to determine maximum temperature, duration above 60oC and degree-seconds at a base of 60oC. Following fire, plants were returned to the greenhouse and watered to maintain good growing conditions. Plant response was assessed using standing crop and live tiller counts. Three weeks following Experiment 2 fires, tiller counts were negatively related to fuel load for B. gracilis, H. comata and P. smithii. Regression models indicated one tiller lost for every additional 347, 184 and 885 kg/ha of fuel between 5000 and 9000 kg/ha for B. gracilis, H. comata and P. smithii, respectively. The 500 to 4500 kg/ha fuel loads common to most of the Northern Plains appear to offer little risk of tiller loss. Despite negative relationships of live tillers with heavier fuel loads, no plant mortality has been observed.