A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation starting in rural and urban areas. Some forest ecosystems in their natural state depend on wildfire. Depending on the type of vegetation present, a wildfire can also be classified more specifically as a bushfire (in Australia), desert fire, grass fire, hill fire, peat fire, prairie fire, vegetation fire, or veld fire. Wildfires are distinct from beneficial uses of fire, called controlled burns, though controlled burns can turn into wildfires.
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Fossil charcoal indicates that wildfires began soon after the appearance of terrestrial plants approximately 419 million years ago during the Silurian period. The occurrence of wildfires throughout the history of terrestrial life invites conjecture that fire must have had pronounced evolutionary effects on most ecosystems' flora and fauna. Earth's carbon-rich vegetation, seasonally dry climates, atmospheric oxygen, and widespread lightning and volcanic ignitions create good conditions for fires.
Wildfires are often classified by characteristics like cause of ignition, physical properties, combustible material present, and the effect of weather on the fire. Wildfire behavior and severity result from a combination of factors such as available fuels, physical setting, and weather. Climatic cycles that include wet periods that create substantial fuels and then are followed by drought and heat often proceed severe wildfires. These cycles are made worse by heat waves and droughts caused by climate change.
Wildfires can cause damage to property and human life, although naturally occurring wildfires may have beneficial effects on native vegetation, animals, and ecosystems that have evolved with fire. High-severity wildfire creates complex early seral forest habitat (also called "snag forest habitat"), which often has higher species richness and diversity than an unburned old forest. Many plant species depend on the effects of fire for growth and reproduction. Wildfires in ecosystems where wildfire is uncommon or where non-native vegetation has encroached may have strongly negative ecological effects. Similarly, human societies can be severely impacted by fires, including direct health impacts of smoke, destruction of property, especially in wildland–urban interfaces, economic and ecosystem services losses, and contamination of water and soil.
Wildfires are among the most common forms of natural disaster in some regions, including Siberia, California, and Australia. Areas with Mediterranean climates or in the taiga biome are particularly susceptible. At a global level, human practices have made wildfires worse than naturally would happen, with a doubling in land area burned by wildfires when compared to natural levels. Humans have contributed to major factors to increased wildfires, increased heat and dry periods due to climate change and other more direct human activities, such as land-use change and wildfire suppression. This increase in fires, creates a negative feedback loop releasing naturally sequestered carbon back into the atmosphere, creating further global warming.