Dye-layer density analysis identifies new Douglas-fir beetle attacks

Two study plots containing Douglas-fir, Pseudotsugamenziesii (Mirb.) Franco, newly infested by the Douglas-fir beetle, Dendroctonuspseudotsugae Hopk., were photographed with large scale (1:1100) color infrared film on 29 July 1979 approximately 3 months after insect attack. Significant differences were found between cyan dye-layer densities, and the green/red and red/infrared ratios of the images of the successfully attacked and healthy trees. Discriminant analysis clearly separated the two image groups with 52 of 53 healthy trees and 9 of 15 successfully attacked trees being correctly classified. It is concluded that trees which have been successfully attacked by beetles can be detected on color infrared air photos approximately 3 months after initial attack while the trees still support visually green, healthy appearing foliage.