Fire has been a key factor in shaping the ecology of the Greater Yellowstone Ecosystem. Native plant species evolved adaptations so they survive and in some cases flourish after periodic fires. Fire influences ecosystem processes and patterns, such as nutrient cycling and plant community composition and structure. Fire regimes in the western United States changed with the arrival of European and American settlers, whose livestock removed grassy fuels that carried fires and whose roads fragmented the continuity of fire-carrying fuels. Most naturally occurring fires were suppressed to the extent possible. The National Park Service aims to restore fire’s role as a natural process in parks when and where this is feasible.
Lightning may ignite dozens of forest fires during a single summer, but most of them go out naturally after burning less than half an acre. Others torch isolated or small groups of trees, become smoldering ground fires, and eventually go out on their own. On rare occasions, wind-driven fires have burned through large areas of forest, as in 1988, when multiple fires crossed more than one million acres in Yellowstone and on surrounding federal lands despite massive efforts to extinguish them. Without frequent small and occasional large fires to create a mosaic of plant communities in different growth stages, biodiversity declines and leaf litter and deadfall accumulate much faster than they can return nutrients to the soil through decay.
Evidence of fires that burned before the park was established in 1872 can be found in soil profiles, charcoal found in lake sediments, landslides, and old-growth trees. Research shows large fires have been occurring in Yellowstone since forests became established following the last glacial retreat 14,000 years ago. Yellowstone’s fire season typically lasts from July to the end of September. The number and extent of fires that occur each year depend on what efforts are made to suppress the fires, as well as environmental conditions such as the number and timing of lightning storms and the amount and timing of precipitation. Continue: Ignition, Fire Behavior, Frequency of Fire