Forest Fires

in most instances, caused by careless handling of fire. Forest fires do heavy damage to forest lands by destroying a great deal of timber, reducing the growth of trees, worsening the composition of forests, and increasing the amount of windfall. They spread harmful insects and tree-destroying fungi and cause soil conditions to deteriorate.

The most common type of forest fire is the surface fire, which burns the forest floor, lichens, mosses, grasses, fallen branches, the undergrowth, and young trees. Surface fires are spread by the wind at a rate of 0.25–5 km/hr. Crown fires engulf both the stand and the moss-grass cover and regrowth. They spread at a rate of 5–25 km/hr. Ground (peat) fires, which burn the peat layer and tree roots, spread at a rate of tens to hundreds of meters a day. Several types of forest fires may occur at the same time. Usually, the type of fire depends on the kind of stand. Crown fires are common among young pines, and surface fires, among mature or old pines and in clear-cut forests. In the spring, most forest fires start in clearings, glades, and dry forests and are of the surface type. All kinds of fires may break out in summer and autumn. In the winter, forest fires are rare, but peat fires sometimes develop under the snow.

Preventive and control measures include education of the public in fire prevention, removal of inflammable material from the forests, and construction of firebreaks and fire lines (strips of land free of trees and bare to the mineral soil). Forest rangers, forest wardens, and observers in airplanes patrol the forests. Television and instruments that are sensitive to infrared radiation are used to detect forest fires. Ground devices and aircraft, as well as forestry fire-fighting equipment (plows and backfiring devices, for example), are used to extinguish fires.

Surface fires are controlled by sprinkling earth around the border of the fire, applying water and fire-extinguishing chemicals, smothering the flames with branches, and starting backfires (that is, burning live and dead vegetation in the path of the fire). Firebreaks 1–2 m wide are built to check large surface fires. Crown fires are usually checked by natural or artificial barriers (clearings, roads, and fire lines). Burning off vegetation and backfires are other methods used to fight crown fires. To control a ground fire, fire-fighting crews surround it with trenches 1 m wide and as deep as the mineral layer or the layer of water-saturated peat. Ground fires are extinguished with water and various chemicals that increase the wetting capacity of water.