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    Author(s): Ralph M. Nelson
    Date: 1952
    Source: U.S. Department pf Agriculture, Forest Service , Southeastern Forest Experiment Station, Asheville, NC. .
    Publication Series: Other
    Station: Southeastern Forest Experiment Station
    PDF: View PDF  (492.0 KB)


    When forest fires burn through southern pine stands, effects on tree crowns range from no observable injury to complete browning and even total con­ sumption of all needles. Mortality and loss of growth that may follow are largely determined by the extent of damage to the foliage, particularly to the buds and twigs. Height of scorch line, as marked by yellowing or browning nee­ dles, is a rough measure vf damage.

    Four major interacting elements determine whether pine needles are damaged by fire. These are fire intensity, initial vegetation temperature, length of exposure to heat, and lethal temperature of needles. Fire intensity varies according to fuel, weather, and rate of spread. Initial vegetation temperature is highly significant because a tree crown on a cold day at a temperature of 4o°F. requires about two-and-one-half times as much heat to reach a lethal tem­ perature as does a crown on a hot sunny day at 100°F. Duration of heat is also a significant variable because the longer needles are exposed to heat the more likely they are to be killed. For example, it can be assumed that a fast-burning headfire which may  subject foliage to heat for only a fraction of a minute will cause less damage than a slow-burning backfire of equal intensity which may take several minutes to pass a given point. Finally, the degree of ability of cells within pine needles to tolerate heat has a direct bearing on the extent of foliar injury .

    The purpose of the study reported here was to determine some of the time­ temperature relations as they affect the death of pine needles. The study is one phase of a project designed to provide information on fire behavior, intensity, and effects which will be helpful in prescribed burning and damage appraisal.

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    Nelson, Ralph M. 1952. Observations on heat tolerance of southern pine needles. U.S. Department pf Agriculture, Forest Service , Southeastern Forest Experiment Station, Asheville, NC. 6 p.

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