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Forests and Trees of the National Park System
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Forest Enemies

Fire is the greatest single destructive force threatening the park forests. During the 20-year period from 1930 to 1949, inclusive, the area of forest, brush, and grass burned over annually within the National Park System averaged 10,990 acres—less than two-tenths of 1 percent of the acreage requiring intensive fire protection. During this 20-year period the average number of fires per annum was 349, of which 234, or 67 percent, were man-caused, and 114, or 33 percent, were set by lightning.

Little can be done to prevent lightning fires, although research has been suggested to determine to what extent the build-up of clouds toward electrical storms can either be dissipated or diverted into normal rain storms without lightning by seeding the clouds with dry ice or some other reactor at the proper time.

As for man-caused fires, every effort is being made, in cooperation with State, private, and other Federal forest protection organizations, to impress upon the public the danger of fire and the means of preventing forest fires.

The Service has developed a well-trained and well-equipped fire control organization, of which the park ranger organizations constitute the backbone. These are augmented by fire lookout observers and fire control aids. In periods of emergency all other personnel of the parks are called on to assist, and, if necessary, additional fire fighters are employed from outside the parks. The fire control record of the Service compares very favorably with that of any other forest protection agency, despite the tremendous number of visitors.

Forest insects take a considerable toll of the forest trees, especially when unfavorable conditions, such as prolonged drought, reduce their vitality and their resistance to the attacks of destructive insects, enabling the latter to build up into epidemic proportions. Within the national parks the chief agents of this type of damage are the bark beetles, which girdle and kill the trees by their galleries in the cambium layer. Other destructive insects are found among the leaf feeders, such as the spruce budworm, the hemlock looper, the needle miner, the tent caterpillar, and the fall webworm. When epidemics develop, they result in widespread destruction and require large sums of money for control. The policy of the National Park Service, therefore, is to maintain a very careful watch for any observable build-up of infestation beyond the normal condition and take corrective measures to prevent the development of serious epidemics.

Tree diseases.—Some of the native fungi and viruses may at times erupt into serious epidemics, as the oak wilt at present. However, the worst troubles in this line have been from introduced diseases. Examples of these are the chestnut blight, which has practically wiped out the native chestnut in the eastern forests; the Dutch elm disease, which is killing large numbers of elms in the East; and the white pine blister rust, a fungus disease introduced on both the Atlantic and Pacific coasts on imported nursery stock.

To preserve representative stands of white or 5-needled pine species in 14 areas of the National Park System, both East and West, the Service is carrying out intensive operations to control the white pine blister rust. These areas contain representative stands of one or more of the following species: eastern white pine, western white pine, white-bark pine, limber pine, foxtail pine, and sugar pine. This white pine blister rust fungus has alternate hosts—a white pine species in one stage of the infection and ribes (currants and gooseberries) during the other stage. The fungus spreads by means of tiny wind-borne spores. When a pine is infected, cankers develop in the bark. Infected pines die when the fungus completely girdles the main stem or trunk or when many of the branches are killed by girdling. The rust cannot be transmitted directly from one pine tree to another but the spores developed by the rust on the pines infect the currants and gooseberries, and the spores from these species in turn infect the white pines. Control for the preservation of the white pines is therefore accomplished by eradication of the ribes.

Insects and tree diseases together are today responsible for greater losses of forest trees than is fire.

Man.—Taking this country as a whole, the human species is the agent responsible for the greatest forest losses. A large share of this is due to man's carelessness with fire, such as throwing away burning matches or tobacco; leaving unextinguished campfires; and failing to prevent the spread of debris-burning fires. Other contributing causes, originating with man, are logging operations, sparks from locomotives, and incendiarism. In commercial forests, failure to leave seed trees or to protect reproduction while logging, or from fire thereafter, has resulted in millions of acres of unproductive forest land. Man is also responsible for much of the forest destruction by diseases and insects by the introductions of foreign pests through inadequate precautions. Fortunately, the areas of the National Park System are exempt from logging operations, and they have experienced a very low ratio of man-caused fires in comparison with the millions of people who visit them. This care on the part of park visitors is a great aid in the protection of national park values.

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Last Modified: Fri, Feb 9 2007 10:00:00 pm PST
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