ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

Most western pine beetle attacks in trees predisposed to fire occur during the
first season after the fire (~iller and Patterson 1927), often accompanied by a
decrease in the number of beetle attacks in the surrounding forest (Craighead 1925).
Post-fire tree killing usually goes on at epidemic levels in the burned areas for 2
or 3 years (Mi 1 ler and Keen 1960) and then wanes after 3 years (Connaughton 1936).
The decline of attacks in burned areas has been attributed to high mortality of
beetle broods (Craighead 1925). The cessation of beetle activity in the burned
areas is often accompanied by an increase in beetle activity in the surrounding
forest (Miller and Patterson 1927), often developing into outbreaks in the nearby
green timber (Stevens and Hall 1960). With prescribed fire, the season when the
burning is conducted is an important factor influencing the occurrence, the duration,
and severity of beetle attack on fire-weakened ponderosa pine (Fischer In press).
The mountain pine beetle also is attracted to fire-killed or weakened western
pines (Jaenicke 1921; Stevens and Hall 1960); in some cases beetle infestations are
reported to have increased as much as 1,000 percent after "1 ight burning" (Jaenicke
1921). More recently, Cronin and Gochnour (In Press) report two instances of in-
creased activity of the mountain pine beetle following fire on the Kootenai National
Forest in northern Idaho. They found: 1 ) a higher percentage of burned trees--
lodgepole, ponderosa, Pinus ponderosa Laws., and western white pine--successfully
attacked than trees that were not burned, and 2) that the larger diameter trees were
more often successful ly attacked. Craighead (1 925) reported that the mountain pine
beetle was not attracted to fire-scorched trees.
A few other species of bark beetles are attracted to pines predisposed by fire.
Sizeable populations of the red turpentine beetle, Dendroctonus valens LeConte, are
often associated with fire-scorched trees (Eaton and Lara 1967) * c a n hasten the
mortal i ty of severely defol iated trees (Herman 1950).
Southern pines injured by fire are also very attractive to bark beetles, resulting
in cpncentrations of beetles in scorched trees, as well as the killing of live green
trees surrounding burns (Beal and Massey 1945).
In addition to the bark beetles discussed above, at least one species of engraver
beetles (fig. 5) is associated with trees predisposed by fire to attack. In the
northern Rockies, the pine engraver beetle, Ips pini (Say), at least during years of
limited activity, not only confines its activities to slash but also to the ". . .
tops of mature trees and smaller groups of standing saplings-and pole size trees
that often have been damaged by the fire or broken off by wind or snow" (Schmitz and
Taylor 1969). Ips beetles are a1 so becoming an increasingly important problem in
connection with prescribed fire. If flame length is not carefully managed, crown
scorch predisposes small, pole-sized ponderosa ine to attacks by pine engravers
(personal communication with Will iam C. Fischer 7 .
The discussion above describes the predisposition of burned forests to bark and
cambium beetles through the weakening, scorching or killing of standing trees,
usually in mature forests. Fires may also predispose forests to bark beetles in an
indirect way when dense forests of a fire-associated species, such as lodgepole
pine , regenerate on the burned areas and become "beet1 e-suscepti bl e" several decades
later (Lotan 1976).