Browsing by Author "Alger, Larry Allen"

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    Previsual detection of stressed coniferous trees
    Alger, Larry Allen (Virginia Tech, 1974-05-06)
    The study consisted of two parts: following the fade rates of killed field-grown Virginia pine (Pinus virginiana Mill.); and to study the effects of different stresses on seedlings. Foliage fade rates of killed field-grown Virginia pine varied with the time of the year the tree was killed. Little variation in fade rates was found between years. Foliage of seedlings grown under stress due to: girdling; sevpring; defoliating; and drought, were studied by paper chromntographv, cross sectioning, and photography. The four pigments found appeared to decline proportionately as the foliage went from green to red. An error in technique resulted in uninterpretable needle cross sections. Photography using black and white, black and white infrared, color, and color infrared films gave no previsual detection of stress.
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    Stress detection in loblolly pine using relative apparent temperatures
    Alger, Larry Allen (Virginia Tech, 1979-05-05)
    The hypothesis that stressed loblolly pine (Pinus taeda L.) could be distinguished from non-stressed loblolly pine by increased foliage temperatures was tested. The foliage temperatures of seedlings and trees were measured with an AGA Thermovision 680 system, imported by the AGA Corporation, Secaucus, New Jersey. The AGA Thermovision 680 system is a simple, easily transported remote sensing system for detecting relative apparent temperatures of plant foliage without direct contact with the leaves. This system is sensitive to infrared wavelengths in the 2-5.6 micron region of the electro-magnetic spectrum. Foliage temperatures in loblolly pine seedlings increased within one week of stress induced by drought, flooding, or severing. Increased temperatures of stressed seedlings were associated with reduced needle moisture content prior to visual symptoms of stress. Foliage temperatures of loblolly pine trees stressed by severing the bole were warmer relative to neighboring control trees. Increased temperatures were detected within one week after severing. Previsual detection of stress can be achieved by measuring foliage temperatures of loblolly pine. The AGA Thermovision should prove to be a useful tool for non-destructive sampling of plant stress, for locating stressed trees, and potential bark beetle infestations.