ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Deterioration of spruce (Picea a. ) and jack pine blowdown in northern Ontario
between 1969 and 1972 was caus- several species of wood borers, especially
Tetro ium m. and sawyer beetles, Monochamus m. (Gardiner 1975). Milling studies
&O to 20 percent loss in all material combined, 1 and 2 years after the
storm. In this case, trees left standing after the storm were not attacked due in
part to rapid salvage of the windthrown material as well as the attraction of emerging
beetle populations to fresh breeding material provided by further blowdown (Gardiner
1975).
In the central Rocky Mountains, major outbreaks of the Engelrnann spruce beetle
have generally been associated with residues created by windthrow, as well as residues
created by logging (~assey and Wygant 1954; Schmid and Beckwith 1972). A severe
wind storm in Colorado in mid-June of 1939 blew down groups of Engelmann spruce in
which comparatively large populations of the Engelmann spruce beetle subsequently
developed. Beet1 es spread from the wi ndthrow residue to the surrounding forests,
and by 1948, 4 billion board feet of spruce timber had been killed (Mielke 1950).
Perhaps the most notable occurrence of windthrown forests creating residues
redisposed to insects in the northern Rocky Mountains involved the Engelmann spruce
geetl e . During the fall of 1949, hurricane-force winds whipped through northern
Idaho and northwestern Montana, transforming cwntless stands of Engelmann spruce
into large volumes of spruce residue. Severe epidemics of the spruce beetle developed
in much of this downed timber during 1950 and 1951, spreading in 1952 to standing
spruce throughout most of the Engelmann spruce timber type in the northern Rockies
(fig. 8). As a result, approximately 2.5 billion board feet of spruce timber was
attacked by this beetle between 1952 and 1956 (Tunnock 1959). During this same
perlod, the forest management plan was modified on several national forests as
thousands of acres of spruce forests were clearcut in northern Idaho and western
Montana to salvage damaged and/or beetle-kil led trees, both standing and windthrown.
The outbreqk steadily declined following its peak in 1953; by the late 1950's no
infestations were reported in many forest compartments.
F