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Spruce Decline Syndrome in the Fort Nelson Forest District Following Prolonged Defoliation by the
Eastern Spruce Budworm
Jennifer Burleigh,
Simon Fraser University, Burnaby, BC, Canada
[From a presentation at the 51st Annual Meeting of the Western Forest Insect Work Conference in
Portland, Oregon from February 7-10, 2000.]
The term "spruce decline syndrome" applies to large areas of the northern Fort Nelson Forest District.
A complex of secondary insects (cerambycids, buprestids, scolytids and siricids), and weak pathogens are
attacking and killing white spruce which had been severely stressed from heavy defoliation by the
spruce budworm,
Choristoneura fumiferana
.
Areas in the northern district have experienced 4-5 budworm outbreaks in the past century, while
stands in the south end of the district have only had 2. Diameter losses in the most recent
infestations were estimated with the use of stem analysis. Mean tree volume losses were
extrapolated to a per hectare total to estimate the economic losses associated with the infestation.
This translated to a mean diameter loss of 36.3 cubic metres per hectare in the southern sites and
22.7 cubic metres in the north. Although the northern site sustained less volume loss on a per
hectare basis, this must be in context of it being at least the 5th outbreak over the stand's history.
The cumulative diameter and height losses, stem defects and woodborer damage substantially increases
the losses in these northern stands. The term "spruce decline syndrome" is being used to describe
those stands that have entered a general state of decline following the collapse of the last budworm
outbreak in 1995.
Decline in the Boreal Forest
Bob Setter, M.P.M., R.P.Bio and
Marnie Duthie-Holt, M.P.M., R.P.Bio, F.I.T.,
Simon Fraser University, Burnaby, BC, Canada
[From a presentation at the 51st Annual Meeting of the Western Forest Insect Work Conference in
Portland, Oregon from February 7-10, 2000.]
An economically based Decision Support System (DSS) for long-term forest development planning in the
boreal forest is being developed. Impetus for this DSS comes from forest licensees in the Fort Nelson
Forest District, BC, where substantial economic losses are occurring as a result of Spruce Decline
Syndrome (SDS). SDS is a term coined to describe the general state of decline of overmature spruce
stands after continued defoliation by the eastern spruce budworm
Choristoneura fumiferana
(Clemens), followed by extensive attack by destructive secondary insects.
Recent groundwork indicates that SDS is currently stressing standing timber inventories. 50% of
sampled stands had >20% host mortality, when examining the number of stems of spruce and balsam, with
many of these stands having mortality levels as high as 80%. Opportunistic secondary insects such as
bark and wood boring beetles are taking advantage of stressed timber, resulting in rapid decline of
affected stands. Infestation rates in standing timber were as follows:
Dryocoetes confusus
3.4%;
Dendroctonus rufipennis
3.4%;
Ips spp.
3.2 %; ambrosia beetles 1.7%; and woodboring beetles 16.1%. These results indicate extensive timber
quality degrade is occurring from woodborer activity in the standing trees, and since a portion of
this activity is occurring in green trees, no inference regarding timber degrade can be made from
aerial survey data. As well, due to constraints of winter-only harvesting, log inventories are often
stored for a year or more post harvest. This storage time allows woodborer activity to continue in
the logyard. Bugbusters logyard management program surveys indicate woodborer infestation rates in
decked inventory reached 77% by August 1998. A mill study conducted in April of 1999 in conjunction
with HALCO Software, examined economic losses and decline rates resulting from wood borer activity.
HALCO’s SAWSIM® Sawmill Simulation Program assessed degrade with the following conclusions. Sawlogs,
which were attacked three years previously by woodborers and those attacked in the logyard were
downgraded from the Japanese Agriculture Standard (J.A.S.) to "Stud", with economic losses totalling,
$62.94/1000m3 and $936.77/1000 m3,
respectively. Due to operational difficulties veneer products were not analyzed, however, this is
where the highest losses were expected. It is hoped that veneer analysis will be rerun in 2000.
A relational database has been constructed to allow forest managers to query economic losses, in a
given cutting permit. A susceptibility model for the risk of forest decline and economic loss is
also being developed, in conjunction with risk maps. The DSS will thus create an opportunity to
proceed with long-term forest development, while mitigating the risk of economic losses resulting
from forest decline. This system will be especially valuable to licensees in the boreal forest,
where overmature stands will need to be stored on the stump for many years.
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