The control of forest fires has developed into an independent and complex science costing approximately $100 million annually in the United States. Because of the extremely rapid spreading and customary inaccessibility of fires once started, the chief aim of this work is prevention. However, despite the use of modern techniques (e.g., radio communications, rapid helicopter transport, and new types of chemical firefighting apparatus) more than 10 million acres of forest are still burned annually. Of these fires, about two thirds are started accidentally by people, almost one quarter are of incendiary origin, and more than 10% are due to lightning.
Modern firefighting practice now recognizes that fires caused by lightning are an important tool of nature. Such fires do away with dead underbrush and diseased areas of growth, leaving clear areas for new growth of grass and new generations of trees. Some trees, it has been found, cannot grow without the aid of fire. The cones of the jack pine, for example, need exposure to intense heat to release seed. Other species, such as the Douglas fir and the sequoia, cannot flourish in shaded areas but need the open sunlit space cleared by fire. For such reasons lightning-caused fires in many cases—especially in wilderness areas far from habitation—are now permitted to burn but are carefully monitored and kept under control.
The potential commercial value of the land lost to human-caused fire cannot be calculated: aside from the loss of timber, the damage is inestimable in terms of land rendered useless by ensuing soil erosion, elimination of wildlife cover and forage, and the loss of water reserves collected by a healthy forest. The increasing demand for water to supply growing metropolitan areas and for agricultural irrigation has stimulated the study of the essential role of forests in water conservation.