Fire effects in the grasslands of Yellowstone National Park

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)




Samuel J. McNaughton


nutrient cycling, Lupinus sericeus, ungulate, grazing, ecology, Cervus elaphus

Subject Categories

Ecology and Evolutionary Biology


Fires burned almost 45% of Yellowstone National Park in 1988. The goal of this dissertation research was to learn how fire would affect grazing by ungulates, plant production and nutrient cycling mainly in the sagebrush grasslands of Yellowstone National Park. Winter, transitional and summer range for ungulates provided the study locations for this project. Findings from this study showed that burning can increase aboveground production in the Yellowstone grasslands. Increases may last up to three years after fire but only on winter range. There were no discernable effects of fire on productivity in summer and transitional ranges. Burned soils on winter range typically held more water and had greater concentrations of phosphorus and ammonium, all of which may contribute to increases in aboveground production. Ungulates consumed more forage in burned areas, but only on winter range in the spring of 1991. Immediately following fire, nutrients become concentrated in ungulate forage--up to 3$\times$ higher than forage on unburned areas. Fires, however, may diminish this nutritional benefit to ungulates because burning also increases the aboveground biomass of unpalatable forbs like lupine (Lupinus sericeus).

Effects of the fire were also compared between a lodgepole pine forest and adjacent grassland. Burning greatly increased the production of grasses growing in the understorey of a lodgepole pine forest even five years after fire. Elk, however, consumed little of this productive forage suggesting that forage quality rather than quantity may influence grazing behavior in some areas of Yellowstone. Data from this dissertation suggest that ungulate activities may influence the productivity of Yellowstone grasslands more than the general physical environment. Overall, the Yellowstone grasslands appear very resilient to burning. Fire effects may require further evaluation during dryer periods to achieve a better understanding of fire's role in the Yellowstone ecosystem.