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An outbreak of Douglas-fir beetle, Dendroctonus pseudotsugae Hopk.,
40-4
began in 1969 in the North Fork Clearwater River drainage in northern
Idaho. This infestation probably resulted from trees felled during
clearing for the Dworshak Reservoir, from ice and snow breakage which
occurred during the winter of 1968-69 in stands adjacent to the proposed
reservoir, and an abundance of mature and overmature Douglas-fir
within the drainage. The outbreak reached epidemic proportions in 1970,
40 but was not detected until 1971.
To determine impact of this insect on Douglas-fir stands within the
area of infestation and establish a base from which to conduct salvage
logging, a two-stage survey using aerial photography followed by a
ground cruise was conducted in 1971, 1972, and 1973. Area surveyed varied from 288,000 acres in 1971 to 494,000 in 1972, and was reduced
410 to 287,000 acres in 1973.
The 1971 survey estimated that 174,164 trees were killed during the
2-year period 1970-71, resulting in a volume loss of 85.8 MMBF of
Douglas-fir sawtimber on 288,000 acres. In 1972, an estimated 46,844
trees were killed with a volume loss of about 17.8 MMBF on 494,000
acres. In 1973, the survey estimated that 8,141 trees were killed with
a volume loss of 4.2 MMIIF of merchantable timber on 287,000 acres. The
infestation has been declining since 1971. |
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