Spruce decline syndrome

The term "spruce decline syndrome" applies to large areas of the northern Fort Nelson Forest District.

On this page:

• History of the decline
• Decision Support System
• Statistics
• Secondary insects
• Relational database

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.

History of the decline

"Spruce decline syndrome" is a term that describes stands that have entered a general state of decline following the collapse of the last budworm outbreak in 1995.

Outbreaks

Areas in the northern part of the district have experienced 4 to 5 budworm outbreaks in the past century. Stands in the south end of the district have only had 2.

Diameter losses

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.

Decision Support System

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, B.C., where substantial economic losses are occurring as a result of spruce decline syndrome.

Statistics

Field studies in 1998 indicated that spruce decline syndrome stressed standing timber inventories. 50% of sampled stands had more then 20% host mortality when examining the number of stems of spruce and balsam and many of these stands experienced mortality levels as high as 80%.

A log yard management program indicated woodborer infestation rates in decked inventory reached 77% by August 1998. As well, a mill study conducted the following spring examined economic losses and decline rates resulting from wood borer activity where sawlogs, which were attacked three years previously by woodborers and those attacked in the log yard 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.

Secondary insects

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.

Relational database

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.