Fire is an event controlled by fuels (like trees, grasses, and shrubs), weather, and topgraphy / terrain. Fire has existed throughout all time periods, and prior to the appearance of humans in North America, the ingredients for fire were largely controlled by climate.
Since human presence, ignition sources and fuels have been modified; people have changed their environment. As a result, ecosystems have adapted to wildland fires, defined as all fires that burn in natural environments. The natural role of wildland fire, an important ecological force, cannot be ignored, because fire greatly influences ecosystems. Fire's influential role as an ecological force, similar to that of other natural phenomena, such as floods, earthquakes, and hurricanes, is discussed in the following sections.