Background: Fire is the most important disturbance agent of global vegetation cover worldwide, affecting between 3 and 4 million km2 annually, and burning of forests and other vegetation is a major driver transferring carbon from the terrestrial sphere to the atmosphere. Despite its importance, fire’s role in climate change, ecosystem dynamics, and carbon and energy balances is still poorly understood. In recent decades, fire activity has dramatically increased around the world to an extent that the size and severity of fires now may be unprecedented on historical time scales. This increase in burning begs the question of whether climate change, human ignitions, land-use change, or some combination of all is responsible. Some of the largest fires are occurring in forests that are highly vulnerable to climate change, have little natural resilience to fire, and are undergoing rapid land-use change. Increased fire size and severity in temperate latitudes have been attributed to warmer temperatures, leading to drier-than-average summers and a longer fire season. In parts of Australia, New Zealand and western North America, current severe drought and plant mortality are also exacerbating fire hazard and raising concerns about the trajectory of post-fire vegetation change and future fire regimes. Concurrently, land-use conversion is occurring at a rapid pace. Forest clearance, fire suppression and related fuel changes, invasive fire-prone plant species, and intensive livestock grazing have increased fire susceptibility and challenge efforts to mitigate fire risks and fire effects. A shift from subsistence and agricultural economies to those based on tourism and recreation has increased population growth at the wildland-urban interface, sharpened the gradient between protected wildlands and rural residential properties, and raised new concerns about the consequences of altered disturbance regimes on ecosystem dynamics, biodiversity, and carbon storage. Land managers and ecosystem scientists are increasingly aware of the benefits of wildland fire for fire-adapted ecosystems, but extreme fire conditions make prescribed fires impractical and lay the groundwork for potentially irreversible ecological consequences.
