ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

The eruption of Mount Saint Helens has raised fears of windthrown residues
predisposing forests to insects. High winds accompanying the 18 May 1980 eruption
blew down mill ions of board feet of Douglas-fir timber growing on the mountain.
Foresters are now worried that the downed residues may become infested with the
Douglas-fir beetle, which may then spread to standing healthy trees farther from the
mountain. Frank Kopecky, deputy regional forester in Portland, Oregon, says that
the beetles could become "a major problem" in two or three years (Missoulian 1980).
RESIDUES CREATED BY OTHER AGENTS
Lightning may predispose trees and forest stands to insect attack when the
struck trees do not ignite and burn. In the northern Rockies, Schmitz and Taylor
(1 969) document an instance where a 79-foot-tall , 24-inch-diameter (24 m, 0.6m) tree
struck by lightning was infested along its entire length by bark beetles--the upper
two-thirds by the pine engraver beetle, the mountain pfne beetle at near mid-bole,
and the western pine beetle and a pine engraver in the lower bole. Moreover, 76 per-
cent o-F the immature trees within 80 feet (24.3 m) of the struck tree were attacked
and became infested with pine engraver beetles (fig. 9). Schmitz and Taylor (1969)
speculated that the infested trees surrounding the lightning-struck tree suffered
lightnin damage to their roots, predisposing them to pine engraver beetle attack.
Schmi tz 9 personal communication) be1 ieves that a 1 ightning-struck tree is probably
the most attractive of what we call "weakened" trees.
Figure 9. --Lightning, Cn addition +o
igniting fires predisposing forests
to insects, often predisposes struck
trees (when not ignited) and those
surrounding them to various species
of bark and engraver beetles. In
the opinion of Dr. R. P. Sch&tz
(persona2 comnicationl , Zightningstruck
trees are probab2y the most
att~active to some insect species of
those trees we caZZ "weakened", by
one cmse or anoeher.