Eastern Spruce Budworm

The eastern spruce budworm (Choristoneura fumiferana) is a tortricid moth commonly referred to as the spruce budworm outside of British Columbia where it is a major defoliator in boreal forests in eastern Canada. These budworms are mostly found in the Fort Nelson Natural Resource District but has also been identified within the Fort St. John Timber Supply Area. The spruce budworm has been associated with the term "Spruce Decline Syndrome".  This term 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.

Eastern spruce budworm defoliation was mapped in 2016 for the first time since 2005.  A single 250 ha patch of spruce was lightly damaged along the Liard River west of Maxhamish Lake.  This budworm has historically been cyclical in nature in the TSA, and it was expected that damage would occur soon, after eleven years with no defoliation observed.

Biology & History

The main hosts of the eastern spruce budworm in the Fort Nelson Natural Resource District are white spruce.The spruce budworm disperse locally after hatching and practice more long-range migration as adults to avoid harsh weather conditions.

Spruce Decline Syndrome

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 part of the 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. The southern sites saw a mean diameter loss of 36.3 cubic metres per hectare and the sites in the north saw 22.7 cubic metres. Although the northern site sustained less volume loss on a per hectare basis,the cumulative diameter and height losses, stem defects and woodborer damage sustained over the 5 outbreaks over the stands history, 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 support system comes from forest licensees in the Fort Nelson Forest District, BC, where substantial economic losses are occurring as a result of spruce decline syndrome.

Recent groundwork indicates that spruce decline syndrome 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. 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 totaling, $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.