Probably the beginning point of any discussion of forest fires is a consideration of their causes. The Forest Service has kept careful records year after year (by calendar and not fiscal years) concerning the cause, the damage, the area burned over, the cost of fighting and many other matters. During the calendar year 1917 there were 7,814 forest fires on the National Forests. Of these the National Forests of California had to contend with 1,862. Of the total number of forest fires 40 per cent. were confined to less than 1/4 of an acre, 28 per cent. to less than 10 acres, while 32 per cent. spread over areas greater than 10 acres. The large percentage of small fires shows how efficiently the National Forest fire protection organization works in keeping the area burned over to the lowest possible acreage.
Causes of Forest Fires on the National Forests. Forest fires on the National Forests originate in many different ways. In 1917, lightning caused 27 per cent.; unknown agencies, 17 per cent.; campers, 17 per cent.; incendiaries, 12 per cent.; railroads, 13 per cent.; brush burning, 7 per cent.; saw mills, 3 per cent., and all other causes, 4 per cent. Thus it will be seen that a very large percentage, at least 60 per cent., of the fires are attributable to human agencies and are therefore preventable. At least 27 per cent, of the fires, those attributed to lightning, are not preventable, and the only way to combat those is for the Forest officer to get to them as soon as possible after they get started. The preventable fires, however, may be arrested at their source, that is, by popular education dealing with the use of fire in the woods these causes can be greatly reduced and, in time, no doubt, eliminated. Therefore, the fire protection problem immediately resolves itself into two almost distinct phases of action—fire prevention and fire control.
Figure 34. A forest fire lookout station at the summit of Mt. Eddy. Mt. Shasta in the background, California
Just how these various agencies start fires may be of interest. Railroads cause fires by their locomotives sending out sparks through the smokestack or dropping hot ashes along the right-of-way. These sparks alight in inflammable material, such as dry grass and leaves, and start a fire. Lightning sets fire to trees, especially dead and dry ones. In the California mountains, lightning storms without rain are frequent and these do great damage. The author has seen as many as nine forest fires started by a single lightning storm inside of half an hour. Incendiary fires are set by people with varying intent. How many are set with malicious intent, just to see the forests burn, is not known, but many fires are started by people setting fires to drive game, to improve the pasture, to make traveling through the woods easier, or for other reasons. Brush burning includes those fires which start from settlers clearing land and burning the brush and thickets. Campers cause a large percentage of the fires by leaving their camp fires burning. Instead of extinguishing them before they leave camp, careless people let them burn; a wind blows a few sparks into some dry leaves or grass nearby, and the fire is started. Many forest fires also start around logging camps by sparks escaping from logging engines, or by setting fire to the slash that is left after logging and allowing these fires to get beyond control.
Behavior of Forest Fires. Fires behave differently, once they get started, depending upon the character of the timber, the amount of wind, and the degree of inflammability of the forest cover. Ground fires burn the inflammable dry grass, needles, dead twigs, etc., on the ground; crown fires are much more severe and, being usually fanned by a heavy wind, run through the tops or crowns of the trees; brush fires burn the bushes and dry shrubs from 5 to 10 feet high; timber fires consume the entire forest—crown, stem, ground cover, and undergrowth—and usually occur in timber that stands close together.
Losses by Forest Fires on the National Forests. The results of forest fires naturally vary with the kind and intensity of the fire. Crown and timber fires do the most damage, and ground and brush fires do less. While the ground fires and brush fires seem to do very little damage to the valuable timber, still they may greatly reduce the productive power of the soil and destroy the watershed cover. Severe ground fires may kill valuable timber by girdling the trees. The great fires of August, 1910, which swept northern Idaho and western Montana destroyed millions of dollars' worth of timber and 85 human lives, and cost the United States $839,000 for fire fighting. These were timber fires and they occurred for the most part in valuable stands of dense timber.
The forest fire losses on the National Forests for the last 9 years show a very great and gradual reduction of losses due to forest fires. In 1908, the total loss through fires was $451,188 and in 1909 it was $297,275. In 1910, the year of the great fires in Montana and Idaho, there were very heavy losses in timber and human lives, due to an unusual combination of dry weather and high winds. But in that year the fire organization was not complete; it had never really been tried out. In this year the organization received its first severe test, and while it did the best it could with the available men and equipment, the situation in Idaho pointed out conclusively the weak points and the short-comings. The proof of these statements is found in the statistics of the next 5 years, when the average total loss for 1911 to 1915, inclusive, was $293,000, and, it must be remembered, several of these years were equally as unfavorable, so far as dry weather and high winds were concerned, as the year 1910. During these years, however, the fire fighting organization had a good chance to be tried out thoroughly; for, as is quite evident, experience is the greatest teacher in this kind of work. During the calendar year 1916 the fire losses reached a new low level, compared to other years, the losses amounting to only $198,599. In 1917 they were higher.
Figure 35. A forest fire lookout station on the summit of Brokeoff Mountain, elevation 9,500 feet. Lassen National Forest, California. Photo by the author.