The high mountain forests of western North America need fire. Fire returns nutrients to the soil and replaces old stands and ground debris with young forest. Intense fires are a characteristic of the conifer forests, though they occur infrequently—once every 100 to 300 years.
The year 1988 brought one of those infrequent, severe fires to Yellowstone National Park. Drought and high temperatures combined to create extreme fire conditions. Fifty wildfires ignited, seven of which grew into major wildfires. By the end of the year, 793,000 acres had burned.
This false-color image, taken by the Landsat 5 satellite in 1989, shows the burn scar left on the landscape (orange and red) by the 1988 inferno. It takes many decades for a conifer forest to recover to pre-fire conditions, and through the use of Landsat, researchers have been able to chronicle the recovery over the past two decades. See the year-to-year images in Earth Observatory’s World of Change article: Burn Recovery in Yellowstone.
Western conifers burn when temperatures are high and plants and soil are dry. Such conditions will come together more frequently as the climate changes over the next century, and fires are already becoming more frequent. A 2011 study combined several climate models to estimate how fire could change in the Yellowstone ecosystem. Yellowstone is near a tipping point, the researchers assert, as warmer, dryer conditions will likely allow large fires to burn as frequently as every 30 years.
When fires occur infrequently, the forest has time to recover. More frequent fires, however, give the conifers little time to grow back. If this occurs, Yellowstone could lose its dense conifer forests and replace them with low montane woodland and grassland by 2050.