Wildfire is the uncontrolled burning of large areas of vegetation. Depending on where they occur, such fires may also be called brushfires, bushfires, or forest fires. Wildfires may be ignited by human activities or by natural causes. Such natural causes include lightning, volcanic activity, or even intense sunlight. A wildfire can happen in any area with vegetation. Such areas include forests, grasslands, and shrublands. Certain ecosystems need occasional wildfires for proper health and growth. An ecosystem consists of all the living things in an area and the nonliving things on which they depend.
Wildfires occur on every continent except Antarctica. They are most common in the temperate forests and grasslands found midway between the equator and the poles. They are less common in tropical and desert ecosystems.
Experts often divide wildfires into three categories: (1) ground fires, (2) surface fires, and (3) crown fires, also called canopy fires. Ground fires burn directly on or below the surface of the ground. Surface fires burn the grass and low-lying vegetation as well as the trunks of trees. Crown fires move across the ground, up the trees, and across the crowns (tops) of the trees. Crown fires are the most dangerous and destructive class of wildfire. 
In ecosystems frequently burned by wildfires, vegetation has evolved certain adaptations. For example, pine trees have thick bark to guard against heat. Also, certain grasses sprout soon after their aboveground leaves are destroyed. Certain shrubs have seeds that are triggered to sprout by the heat and chemicals released by fire, another adaptation to wildfires.
The intensity of a wildfire depends on the vegetation fueling it, the terrain, and the weather. Different fuels release different amounts of heat energy when burned. For example, trees usually burn with more energy than do grass or shrubs. An abundance of trees can therefore fuel an intense forest fire. Terrain, also called topography, affects how a fire spreads. Fire typically moves faster uphill than downhill, because hot air rises. The rising heat ignites fuels upslope. Bodies of water, rocky areas, and roads may slow a wildfire. Air temperature and humidity alter the speed with which fuel burns. Moisture on the ground can slow a wildfire. Also, wind can determine the direction and the rate of a fire’s spread.
Aboriginal people of Australia and certain Native American peoples have used wildfires for thousands of years to change vegetation and wildlife habitat in some areas. By the early 1900’s, however, wildfires had been prevented in developed countries to protect human settlements and natural resources. Prevention has been so successful in some areas that controlled fires must be used to restore plant life and reduce fuels. This practice is called prescribed burning. Nevertheless, prevention did not protect Australia from the bushfires that ravaged the country in late 2019 and early 2020. In the 2010’s, prolonged drought conditions and periods of record high temperatures extended the duration and severity of Australia’s bushfires. Most scientists believe climate change was the driving force behind these conditions. They pointed to the bushfires as an example of how climate change can increase the scale of natural disasters.
