Do you have a story to tell about a fire?

Fire

Lightning and volcanoes have been setting fire to dry vegetation ever since there first evolved vegetation to be set fire to. Humans are relatively late on the scene, but have been using fire for their own purposes for a long time, whether to keep warm, to cook food, to fire pots, to smelt metals, or to clear land for farming, mining, or hunting. Nowadays we use fire for a wide variety of chemical processes, yet still use it for the old purposes too. Evidence in the form of sudden increases in the amount of charcoal deposits in soil tells archaeologists when people arrived at the various islands in the Pacific, for example. In the case of small islands, the old ecosystems never had the chance to recover. The islanders tended to bring their own food plants and animals with them.

Fires are not all harmful. Some trees rely on fires to propagate, for example, and some creatures take advantage of the resultant new grass or dead trees. Fires prevent savannah and grasslands from becoming forest. Fires have been a natural part of the scheme of things since time immemorial, but the more frequent fires that humans set are damaging.

Tropical, moist forests tend to have very lush vegetation, which leads people to believe that it will be very good for farming. So, they use a technique called slash and burn to clear the land. The burning releases potassium and phosphorous into the soil. The nitrogen that was stored in the vegetation is released as nitrogen oxides into the air. In the first year, the crops grow very well as a result. However, rain washes away the nutrients from the cleared land and humans may remove more with the crops, so the land becomes useless after a few years. The soil may also be washed away. A lot of carbon dioxide, a greenhouse gas, is released into the atmosphere.

Studies have shown that if a tropical moist forest experiences a fire, that opens up the canopy and allows more of the forest to dry out, making it more vulnerable to further fires, and the trees killed in the first fire provide fuel, as do the grasses and weeds that come in. Subsequent fires are faster-moving, longer-lasting and more intense.

Slash and burn of farming can be sustainable, but only if population density is low, so that people have available ten times the amount of land that they need to produce crops in any one year. They use each tenth for 2 years then leave it to recover. Recovery takes about 20 years, assuming that there is still native flora and fauna nearby to re-colonize the land. This is called shifting cultivation. Slash and burn is also used to clear land for timber harvesting, and in disputes over property and land rights. Fire is being used a lot in the Amazon and in Central America to clear forests, and in Africa to clear savannah. Forty percent of the world's carbon emissions from global biomass burning each year comes from burning savannah.

Burning forests for farmland, mining, or cattle ranching (for burgers), or to clear last year's crops to release nutrients and kill pests, does not only affect the land. The smoke and gases released into the air can create haze and smog that affect the health of those down wind, as has happened often in Indonesia and Malaysia in recent years, for example. They can even reduce the amount of sunlight that plants receive, reducing crop yields. Sometimes fires that are intended to be small rage out of control.

Of course, not all fires are started deliberately. Some are started by lightning. But in places like the U.S., sometimes those whose job it is to fight fires set some deliberately, believing that pre-emptive action will prevent greater harm from wildfires later in the season. Additionally, some fires are started accidentally either through careless use of fire or through broken glass acting as a lens, or through sparks from machinery. On top of that, there is arson. So, one way or another, some areas see a lot more fires than they would have seen in the past (humans are responsible for as many as 90% of fires globally). On the other hand, there is a lot more effort to put out fires than there used to be, at least in the United States.

Because of the vast increase in our population, and our greater investment in housing and belongings, we are far more at risk from fire than in the old days, when we could gather up our few belongings and run, and resettle in an area that the wildfire missed.

Satellite images allow us to see many of the fires from space, as they are so large. Estimates of the amount of land burnt based on satellite images can vary considerably from estimates provided by governments. It also is difficult to estimate the costs in human health as people suffer and even die from asthma. Even more difficult is estimating the economic costs - the loss of land that could have been much more valuable if it had been used in a sustainable fashion (feeding a family for generations rather than a farmer for 10 years), the work days lost due to ill health, and the loss of tourism due to smog or loss of scenery or danger from fires, loss of topsoil, and damage from mudslides or floods. And most of all, there is the loss of biodiversity, whose value is incalculable. Smog and floods also make for conflict between neighbours.

It is likely that global warming will make some areas far more prone to fires in the future.

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