Forest Fires

INTRODUCTION
Forest Fires, natural or human-caused fires that burn forest vegetation. Foresters usually distinguish three types of forest fires: ground fires, which burn the humus layer of the forest floor but do not burn appreciably above the surface; surface fires, which burn forest undergrowth and surface litter; and crown fires, which advance through the tops of trees or shrubs. It is not uncommon for two or three types of fires to occur simultaneously. Fire management programs are extensive in the United States and other countries (see Conservation: Forest Conservation). Programs include fire prevention, fire fighting, and the use of fire in land management.
FIRE PREVENTION
Most forest fires result from human carelessness or deliberate arson. Fewer fires are started by lightning. Weather conditions influence the susceptibility of an area to fire; such factors as temperature, humidity, and rainfall determine the rate and extent to which flammable material dries and, therefore, the combustibility of the forest. Wind movement tends to accelerate drying and to increase the severity of fires by speeding up combustion.
By correlating the various climatic elements with the flammability of branch and leaf litter, the degree of fire hazard may be predicted for any particular day in any locality. Under conditions of extreme hazard, forests are closed to public use.
Although organizations involved with fire control have traditionally fought all fires, certain fires are a natural part of the ecosystem. Complete fire exclusion may bring about undesirable changes in vegetational patterns and may also allow accumulation of fuel, with increased potential for feeding catastrophic fires. In some parks and wilderness areas, where the goal is to maintain natural conditions, lightning-caused fires may be allowed to burn under close surveillance.
FIRE DETECTION AND FIGHTING
One of the most important aspects of forest-fire control is a system of locating fires before they are able to spread. Land-based forest patrols and lookouts have been largely replaced by surveillance aircraft, which detect fires, map their locations, and monitor their growth.
Ground fires, once established, are difficult to extinguish. When the humus layer is not very deep, a ground fire may be extinguished with water or sand. Most ground fires, however, are controlled by digging trenches around the burning area and allowing the fire to burn itself out. Surface fires are limited by clearing the surrounding area of low vegetation and litter, or digging emergency furrows to confine the area. Crown fires are difficult to extinguish. They may be allowed to burn themselves out, they may be halted by streams, or they may be limited by backfired areas. Backfiring consists of carefully controlled burning of a strip of forest on the leeward side of the blaze, so that when the fire reaches the burned area it can go no farther.
FIRE IN LAND MANAGEMENT
Foresters may purposely ignite prescribed fires under carefully controlled conditions to remove unwanted debris following logging, to favor tree seedlings, or to keep fuels from accumulating. Since most grasses and shrubs grow well after fires, and animals are attracted to the tender and nutritious new growth, prescribed fires often benefit both wildlife and livestock. The mosaic of vegetation of different ages that results from frequent small fires favors a rich diversity of plant and animal life.
Forest fires are often set deliberately to clear forested areas for grazing or agricultural purposes. In slash-and-burn cultivation, subsistence farmers burn small plots of forest for space to grow crops. After two or three years, when the nutrients in the soil have been depleted, the plots are abandoned and other plots are cleared by fire. Large-scale agricultural operations use similar methods to clear forested areas. These practices, along with logging operations, destroyed much of the world’s tropical rain forests during the 1980s and 1990s. The El Niño weather pattern of 1997-1998 disrupted rainfall patterns, leaving many forests dry. Thousands of deliberately set forest fires raged out of control in Indonesia, Brazil, and Mexico, burning millions of hectares of rain forest. Thick clouds of smoke blanketed vast areas in Southeast Asia, South America, and Central America, sending tens of thousands of people to hospitals with respiratory illnesses related to the Air Pollution.