ENVIRONMENTAL CONSEQUENCES in rocky mountain coniferous ...

(1974) determined that the time of year in which timber is harvested affects the
severity of killing of pine seedlings by both the pitch-eating weevil and the pales
weevil, Hylobius pales (Herbst). In pine cuttings made after June and through the
summer and fall, older weevils were attracted to the fresh stumps, from which they
emerged to attack newly winter-planted seed1 ings.
Residues created by pruning in red pine forests also have been associated with
populations of the pine root collar weevil, Hylobius radicis Buchanan, but were
related to a decrease, rather than an increase, in o m n s and damage (Wilson
1967). Based on his previous research (Wilson 1966 ! , and behavioral studies with
the weevil , Wilson pruned the lower 3-5 whorls of branches from young red pines.
This pruning, along with duff removal and soil scraping, allowed heat and light to
penetrate the normally cool, dark daytime habitat of the weevil, reducing larval
populations below an economic level for at least 1 year (Wilson 1967). Branch
pruning to snow depth also has been reported (Miller 1967) to adequately and permanently-control
populations of the European pine shoot moth, Rhyacionia buoliana
(Schiff) .
The sequoia pitch moth, Vespamima sequoiae Hy. Edw., which infests pruned
conifers, provides an interesting example of forest residues predisposing trees to
insects through intense cultural practices. Fresh pruning scars, often associated
with fuel-break pruning (Powers and Sundahl lW3), and associated resin flow where
the living limbs are attached, attract the pitch moth (Weidman and Robbins 1947).
Pitch moth attacks cause an additional accumulation of pitch, but larvae and pupae
both tolerate it and are not drowned in the excessive amwnt of pitch exuded by
attacked trees (Weidman and Robbins 1947). A1 though pitch moths usually do not kill
trees, their attacks may weaken trees and render them more susceptible to bark
beetles, Dendroctonus and I s (Weidman and Robbins 1947). Aesthetic changes in
trees, resin masses, and f f- owing pitch, may be the most important consequences of
pitch moth attacks (Powers and Sundahl 1973). Pitch moths are also attracted to the
large flow of resin at sapsucker drillings (Weidman and Robbins 1947) and to the
wounds in the tree boles resulting from increment borings made by the investigators
(Powers and Sundahl 1973).
In the stumps and slash of khinned red pine in Ontario, Martin (1965) found
three groups of insects of potential economic importance--wood borers, bark beetles,
and weevils. Although the wood borers are usually economically important because
they downgrade sawn products, the red pine thinnings in this case were used for
pulp, and wood borers were not of particular importance. One species of weevil,
Pissodes approximatus, breeds in stumps, slash, logs, and dead standing trees; in
Martin's study, this species killed many trees that may otherwise have survived
drought, disease, planting shock, or other factors. Martin (1 965) found that insects
avoided or were not successful in establishing themselves in living stumps that were
root-grafted to 1 iving trees.
In eastern Canada, many bal Sam fir trees damaged by the eastern spruce budworm
are reportedly killed by the secondary attacks of the balsam bark beetle, Pityokteines
sparsus Leconte. More trees are killed by the beetle in logging areas, indicating
that logging residues are associated with an increase in beetle activity, since
fewer trees were killed by beetles in areas where both logging and slash were absent
(Graham 1922). In many areas of Montana and Utah, opulations of Pit okteines and
Pit o enes build up in logglng and thinning slash, ! hen move to t h b r a n c h e s
h e s i d u a l ponderosa pine. In some areas, nearly every branch is attacked
during the year when residues are created, with some branch killing the following
year. Populations appear to wane after the second year.