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Western spruce budworm (Choristoneura freemani) is a common and destructive native defoliator found in Interior Douglas-fir (Pseudotsuga menziesii var. glauca)
forests that affects tree growth and stand structure. Short-term changes in stem
density and periodic annual increment (basal area and volume) were compared
among treatments for a period overlapping an outbreak of western spruce budworm
(WSB) (2002–2012) and a period of WSB inactivity (2013–2017). In this
pilot study, there were two blocks with each containing three treatments. The
treatments included a no-harvest Control, a Logged treatment with a target basal
area of 15 m²/ha, and a Logged-thinned treatment that included pre-commercial
thinning post harvest. During the active WSB period, there was stem loss and
little increase in volume in the Control and Logged treatments. There was minimal
stem loss and little increase in volume in the Logged-thinned treatment. In
the inactive WSB period, volume growth improved in the Control and Logged
treatments and in one Logged-thinned treatment unit, while in the other Loggedthinned
treatment unit growth did not improve. Among treatments in both time
periods, the Logged-thinned treatment volume growth remained positive while
the Control and Logged treatments were either negative or positive. In the 2017
PrognosisBC model projection, long-term growth (up to 2092) improved for all
treatment units except a Logged-thinned unit where there was low stocking in
the smaller-diameter classes. Despite this, projected growth in the 2012 and
2017 models showed that the Logged-thinned treatment exceeded the Logged
treatment on both blocks. The best-performing partial-cut treatment unit (block 1
Logged-thinned) reached 200 m³/ha of merchantable volume 55 years after the
harvest, suggesting that the post-harvest basal area of 16 m²/ha was too low for
a 40-year planned re-entry. When an option in PrognosisBC was used to simulate
an extended period of WSB inactivity, there was an improved growth response
over the model base case in the partial cuts but not in the Controls, implying
potential growth benefits to manipulating structure and controlling for WSB.
Waterhouse, M., Bradshaw, B.. 2021. Western Spruce Budworm Impacts on Stand Growth in Dry Douglas-fir Forests, Central British Columbia. MFLNRORD. Technical Report (FLNRORD). TR138
Topic: FLNRORD Research Program
Series: Technical Report (FLNRORD)
Keywords:
ISSN:
Scientific Name: Pseudotsuga menziesii var. glauca
ISBN: 978-0-7726-8051-8
English Name: Rocky Mountain Douglas-fir
Other Identifier:
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