Some wildfires smoulder underground for months without a visible flame
Not every wildfire roars through treetops. Ground fires creep through buried roots, peat and forest duff, smouldering for days or months. In Indonesia, a scheme to create rice fields drained peat swamps in Kalimantan and Sumatra, and the dried peat caught fire. Coal seams elsewhere burn by the thousand, sometimes igniting the surface.
A wildfire is any unplanned, uncontrolled blaze in burnable vegetation, variously called a forest fire, brushfire or bushfire. It needs the three sides of the fire triangle: fuel, enough heat and oxygen from the air. Moisture resists ignition because heat must first boil water away before material reaches its fire point, which is why shady, humid, dense forests tend to burn less readily than open grassland.
Fires are classified by their fuel. Surface fires consume leaf litter, grass and low shrubs, usually below about 400 degrees Celsius, though slopes and wind speed them up. Ladder fires climb through small trees, logs and vines towards the canopy, helped by invasive climbers such as kudzu. Crown fires race through treetops once conditions allow, and human-lit blazes that replace whole stands can push into the Amazon, a forest poorly adapted to heat and drought.
People start most fires. In the United States, over 85 per cent are caused by human activity, from campfires and power line failures to sparking machinery like chainsaws and mowers. Arson accounts for a smaller share than often assumed; in California it is typically 6 to 10 per cent a year. Natural sparks come from lightning, volcanoes, rockfalls and spontaneous combustion, while tropical farmers often clear land by slash-and-burn in the dry season.
Fire is not purely destructive. Many ecosystems evolved with it, and some plants need it to grow and reproduce, which is why foresters set prescribed burns, though these can escape. The worst fires often follow wet years that build up fuel and then drought and heat, a cycle climate change has intensified. Globally, human influence through warming, land use and fire suppression has roughly doubled the area burned compared with natural levels, and the carbon released feeds back into further warming.
Source: Wildfire
