File:Bulletin (Pennsylvania Department of Forests and Waters), no. 35 (1923) (20474858496).jpg

Title: Bulletin (Pennsylvania Department of Forests and Waters), no. 35
Identifier: bulletinpennsylv35penn (find matches)
Year: 1923 (1920s)
Authors: Pennsylvania. Dept. of Forests and Waters
Subjects: Forests and forestry
Publisher: Harrisburg, Pa. : The Department
Contributing Library: Penn State University
Digitizing Sponsor: Lyrasis Members and Sloan Foundation

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s Stem Fires, if not Extinguished Promptly, Oftex Spread to the Surrounding Ground Litter and Develop into Surface Fires ally accompanied by, surface fires. Conifers are more subject to such fire, but young hardwoods with new or dead leaves are also liable. Thicket and pole stages are most likely to suffer in the East, especially new coniferous plantations. Crown fires occur when the wind is high and the woods are very dry. The strong draft carries sparks far ahead starting new fires either crown or surface. The general shape developed is that of a "V", although the same factors influencing the shape of a surface fire affect the develop- ment of a crown fire. Without a wind, however, crown fires are prac- tically impossible. The rate of progress is ordinarily from two to three miles an hour or in extreme cases, six to ten miles. It depends upon density of crowns, regularity of heights of trees, and of species. An admixture of non- inflammable crowns or a belt of hardwoods may entirely break a crown fire. Underground fires are those which burn beneath the general surface of the soil. They occur where the mineral soil is covered with an accu- mulation of vegetable material, and, on account of its peaty character, hum more slowly than surface fires. They are common in the northern woods where faHen leaves, needles and other debris decompose very slowly and a deep layer of partly decayed vegetable matter accumulates. Sometimes this may be two or three feet deep. Sphagnum swamps, dried up lake basins, and areas covered with a dense mass of bracken are also likely to be visited by ground fires. When this material becomes dry it burns slowly but with intense heat and is difficult to extinguish. Ordinarily they will not cover more than a few acres a day. They may be accompanied by a surface fire, or even a crown fire, and may develop from either. LESSON ELEVEN KINDS OF FOREST FIRES (Continued) In Pennsylvania most of our forest fires are surface, or brush fires. A few are stem fires, resulting in surface fires, and only in periods of severe drought do we have a crown or an underground fire. A surface fire is one which passes over the surface of the soil and feeds upon dead foliage, dead weeds, dry grass, dry moss, and scattered inflammable debris littering the ground, also occasionally brush and small trees. A part or all of the litter and humus which make up the forest floor is consumed and ((uickly changed from its organic form to ashes. If the fuel on the ground is sufficient a surface fire may develop into a crown fire, especially in young coniferous stands. The manner of burning, the form of area burned over, the rapidity of progress, and the intensity of the fire, depend upon the following factors: 1. Character and quantity of inflammable material. 2. Topography. 3. Character of soil. 4. Condition of atmosphere. A surface fire on level ground and with all factors constant is at first a small circle of flame, gradually spreading in all directions. If the least wind is blowing it burns more rapidly in the direction toward which 29 INTENTIONAL SECOND EXPOSURE

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