La photographie aérienne couleur infrarouge à petite échelle et l'inventaire des dégâts causés par la tordeuse des bourgeons de l'épinette

Since 1970 northeastern North America has experienced a spruce budworm (Choristoneura fumiferana (Clem.)) outbreak. In Quebec, at the end of 1974, some tree mortality was reported for an area of approximately 3 million acres (1,200,000 ha) of pulpwood stands while severe defoliation occurred over 33 million acres (13,300,000 ha). In an effort to improve current methods used to estimate the extent of forest insect damage over large areas, a remote sensing study was initiated with high altitude color-IR aerial photographs (scale 1:60,000) taken over the Gaspé peninsula in mid-August 1974. Cumulative past feeding was apparent at this period of the summer, as almost all current year chipped needles had fallen. Only very severe damage of one year feeding or more could be identified on the images. Colour variations due to stand characteristics such as density, age, rate of growth, prevent the detection of lighter damage on high-altitude CIR photographs. The relative importance of these factors is discussed. For instance a moderately defoliated dense stand can easily be confused with a more open healthy one. It seems that the two main stand characteristics affecting color tonality are density and length of annual shoot growth which is mainly function of age and site quality. Forest insect damage has been more successfully detected on large (up to 1:2,000) or medium (1:4,000-1:12,000) photo-scales. Normal color film may give better information on defoliation levels. As long as objectives are met, the smallest possible photo scale should be used since cost is reduced because fewer photographs have to be purchased and handled during photo-interpretation work.