ELK SURVIVAL FOLLOWING THE 1988 YELLOWSTONE FIRES - A SIMULATION EXPERIMENT

Extensive fires in 1988 burned 22% of the northern winter range in Yel lowstone National Park, which provides critical winter habitat for one of the largest free-ranging herds of elk (Cervus elaphus) in North Am erica. The winter of 1988-89 was moderately severe, and the combinatio n of forage loss due to fire plus deep snows led to high elk mortality (similar to 40%). We designed a simulation experiment to explore how elk mortality that winter might have been different under alternative weather conditions, spatial patterning of the burn, and initial elk nu mbers. The simulations were performed with the Northern Yellowstone Pa rk model (NOYELP), a spatially explicit model of forage availability, snow conditions, elk movement and foraging, and elk energetics. Result s supported earlier findings indicating that snow depth and water equi valent were major determinants of elk survival: in a mild winter scena rio, there was almost no mortality even with forage loss from the fire , but when the most severe winter in recent history was simulated, cal f mortality approached 100%. Under moderate to severe winter condition s, fire pattern and initial elk density also were important. Burning 2 2% of the northern range at random or in single large patches produced higher mortality than did the actual burn pattern. This study also sh owed that mortality increased nonlinearly as initial elk density incre ased, with thresholds in density at which mortality went up sharply. M odeling experiments of this kind can help managers of natural areas si milar to Yellowstone National Park anticipate the effects of future la rge-scale fires, and can provide insights into likely effects of manag ement activities such as prescribed fire.