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Effects of air-photo scale on early detection of Mountain Pine Beetle infestation

University of British Columbia

Colour-infrared positive transparencies, at scales of 1:1000, 1:2000, 1:3000 and 1:4000, were obtained of a lodgepole pine (Pinus contorta Dougl.) stand which was undergoing an active mountain pine beetle (Dendroctonus ponderosae Hopkins) infestation. Visual and densitometric photo-interpretation techniques were applied to these transparencies to determine if symptoms of incipient mortality could be detected from green-foliaged trees following attack by mountain pine beetle. The purpose of this study was to determine the efficiency of photo-interpretation at scales 1:1000, 1:2000, 1:3000, and 1:4000 for early detection of mountain pine beetle-attacked trees. Visual interpretation involved classification of trees into damage types. Subsequent ground-checking allowed a determination of accuracy of damage type classification at each scale. Results indicated that 15% fewer trees were correctly classified as healthy at 1:4000 than at 1:1000. Separation of healthy from attacked trees was achieved with an overall accuracy of 89% at 1:1000, 83% at 1:2000, 91% at 1:3000, and 83% at 1:4000. The interpretation process at 1:4000, however, was considerably slower than at the larger scales. Total green (TG), total red (TR) and total infrared (TIR) film response values of the images of newly-infested trees differed from measurements of the healthy trees. At 1:1000, images of newly-stressed trees indicated significantly higher (p<.05) TIR response values relative to TG and TR film response values, when compared with non-attacked trees. Significant differences were measured for the TG and TR response values, for recently-attacked lodgepole pine, at 1:2000, 1:3000 and 1:4000, which suggests some change in the green-red portion of the spectrum. Visually the foliage of the recently-attacked trees was green. Densitometric interpretation of the photographic data is affected by scale change. There were significant differences in the degree of film response for the 1:4000 photographs when compared to other scales. This would suggest a significant reduction in the reaction of the film dye-layers to reflected light, with decrease in scale. The results of this study indicated that visual interpretation of 70 mm colour-infrared photographs would provide the forest manager with a valuable management tool for early detection of mountain pine beetle attacked timber compared to other methods, such as aerial sketch-mapping, which generally rely upon foliage colour change for recognition of dead lodgepole pine.

Text

2010-04-20

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http://hdl.handle.net/2429/23948

Forestry

University of British Columbia

Graduate