The United States Forest Service, National Park Service, and State Forestry services have been studying and keeping records of the fires and their causes for a very long time now. The idea has been to constantly find improved ways to prevent fires or to contain them. In this, they have had some success, though not always in orthodox ways.
By far, the greatest cause of wild fires in the western US has been lightning strikes. As many as 80% of wildfires yearly are directly or indirectly caused by lightning strikes. Indirect lightning caused wildfires are primarily those that are spawned off of other wildfires. When trees such as pines burn intensely hot, they can explode, throwing burning debris a great distance, causing other fires. Sparks carried by the wind can also cause flare-ups as far as several miles from the main fire.
A secondary cause, resulting in far fewer fires, is by the activities of man. This is primarily in two forms: Carelessness and arson. Carelessness includes incidents where people leave smoldering camp fires unattended, flick lit cigarettes out the car window into tender dry leaf litter, operate vehicles including cars, pickups, 3 and 4 wheelers and motorcycles, in extremely dry conditions where the exhaust pipe and muffler are easily hot enough to catch brush aflame, and cutting firewood in very dry conditions where again, the hot exhaust can cause fire.
The fewest man caused fires come from arsonists, and because of this, the least amount of resources are used to prevent this cause. At the same time, it is interesting to note that in most cases, the arsonists are caught, and the punishment is severe. (Children playing with matches would also fall under this category.)
Punishment is also severe for other man caused fires. Leaving a camp fire unattended or throwing burning material out of car windows generally results in a hefty fine and often expulsion from the forest. If the carelessness results in fire, the cost is far greater. The careless person often finds themselves responsible for paying for several hundred thousands of dollars or more in fire suppression efforts. As with arsonists, the people who carelessly cause fires are usually caught. The forestry departments in all western states also habitually close forests every year during fire season, to help prevent fires due to carelessness. Still, it is interesting that the fires we most often hear about in the media are the ones that are man caused. If they are nature caused, very little is said at all about the cause of the fire, except perhaps, "The cause of the fire is under investigation."
Since lightening caused fires are easily the most numerous, more money and resources are put into prevention and suppression efforts for these fires than any other kind. Thunderstorms are met with a high level of preparedness on the part of the forestry departments, and it isn't unusual for spotter planes to be sent into the air for the duration of the storm. USFS thermal imaging satellites are also used, as they can often resolve the heat of a fire before men can detect the smoke.
The vast majority of lightning caused fires are isolated and contained at less than 5 acres in size. When conditions are right, these can quickly get out of hand, however. In each of the last 10 years, for instance, there has been a fire in excess of 20,000 acres in Washington, Oregon, California, Idaho, Nevada, Utah, and Montana. During most of those years, there have been several, and occasionally the fires merge to create a very dangerous and destructive situation. In 2006, for example, a total of around 450,000 acres of forest burned in Oregon alone, including 2 fires that were each over 100,000 acres in size.
This is where the unusual fire suppression methods often come into play. We know that for fire to burn, it must have fuel. Dead branches, needles and leaves, dense brush, and dead fall all provide the fuel, and late in the year it is tinder dry. This is particularly true in old growth forests. Thinning practices work well, however there simply isn't the manpower to thin several million acres of forest every year. So forestry agencies have, especially for the past half dozen years or so, been using two methods. The first is to slash burn in the spring, reducing fuels at the time of the year that a fire isn't likely to get out of hand so that the slash burns are relatively safe.
The second way is much older and has been used long before the forests were managed; letting it burn. Lightning caused fires are a natural event and natures way of clearing the debris from the forest floor. With the advent of man's forest management, the fuels were allowed to build up to the point that in many areas, there simply isn't any good way to allow the fire to simply burn itself out. However in other areas, this is a viable solution that is used, though the forestry agencies watch these fires closely so that they don't get out of hand, like they did a couple decades ago when fires were allowed to burn in Yellowstone National Park, destroying a great deal of the forests there.
Though man is not the major cause of wildfire in the western US, man can have a big impact in prevention and suppression of even lightning caused fires. There is a problem, though, in that forestry departments are often very under funded for the work that needs to be done. This is not likely to change until people write to their legislators demanding an increase in funding for the forest departments.
Beyond this, we can all be much more aware less careless when it comes to fire sources. Regardless of the cause of the fire, too, if you are told to evacuate an area due to fire, don't argue just leave. The fewer innocent bystanders that fire fighters have to worry about, the more that they can concentrate on their hard, hot, dirty, backbreaking and dangerous jobs. Let's give them the respect to do their jobs.
(Photo by Axel Rouvin)